In this fresh list, Stephen James O'Meara presents 109 new objects for stargazers to observe. The Secret Deep list contains many exceptional objects, a piece of the only supernova remnant known visible to the unaided eye; the flattest galaxy known; the largest edge-on galaxy in the heavens; the brightest quasar; and the companion star to one of the first black hole candidates ever discovered. Each object is accompanied by beautiful photographs and sketches, original finder charts, visual histories, and up-to-date astrophysical information to enrich the observing experience. Featuring galaxies, clusters, and nebulae not covered in other Deep-Sky Companions books, this is a wonderful addition to the series and an essential guide for any deep-sky observer.

Author of several highly acclaimed books, including others in the celebrated Deep-Sky Companions series, Stephen James O'Meara is well known among the astronomical community for his engaging and informative writing style, and for his remarkable skills as a visual observer. O'Meara spent much of his early career on the editorial staff of Sky & Telescope, before joining Astronomy magazine as its Secret Sky columnist and a contributing editor. An award-winning visual observer, he was the first person to sight Halley's Comet on its return in 1985, and the first to determine visually the rotation period of Uranus. One of his most distinguished feats was the visual detection of the mysterious spokes in Saturn's B-ring before spacecraft imaged them. Amongst his achievements, O'Meara has received the prestigious Lone Stargazer Award, the Omega Centauri Award, and the Caroline Herschel Award. Asteroid 3637 was named O'Meara in his honor by the International Astronomical Union. In his spare time, O'Meara travels the world with his wife, Donna, to document volcanic eruptions. He is a contract videographer for National Geographic Digital Motion, and a contract photographer for National Geographic Image Collection.

The Secret Deep is the fourth title in my Deep-Sky Companions series – the other three books are Deep-Sky Companions: The Messier Objects, Deep-Sky Companions: The Caldwell Objects, and Deep-Sky Companions: Hidden Treasures. Like the third companion, The Secret Deep is an important work because it brings to light a new list of 109 deep-sky objects visible in small telescopes under a dark sky. None of the objects in the Secret Deep list appear in the Messier, Caldwell, or Hidden Treasures catalogues; I've included an additional 20 objects in Appendix B. Owners of this series, then, have at their fingertips more than 450 deep-sky objects to explore.

All the Secret Deep objects are visible from mid-northern latitudes, though five or fewer are best seen from more southerly locations in the Northern Hemisphere or further south. Still, the most southerly object in the Secret Deep list – globular cluster NGC 2298 in Puppis – lies at a declination of ^36^{^} exactly, so it is only 1¼^{^} further south than open cluster M7 in Scorpius, the most southerly Messier object. From the latitude of New York City, NGC 2298 will be 9^{^} above the southern horizon when highest.

I have taken great care to select objects visible through my new 5-inch Tele Vue f/5 refractor (see Chapter 1) under a clear, dark sky. As with some objects in the Hidden Treasures list, several of the Secret Deep objects are surprisingly bright – including some open star clusters visible in binoculars and to the unaided eyes, a few galaxies more apparent than the dimmest Messier ones, and a couple of planetary nebulae with central stars you can spy through large binoculars. Take, for instance, 10.7-magnitude IC 4593 – the White-Eyed Pea planetary nebula in Hercules. A 2½-inch refractor can easily sweep up this object, but many fail to see it because they are fooled by its starlike form at low and moderate powers. But this striking planetary, consisting of a complex system of asymmetrical shells, is a glorious little gem at high magnifications; I've viewed it with magnifications up to 100^ per inch of aperture! Then there's NGC 5846 in Virgo; this fantastic elliptical galaxy not only flanks the celestial equator, but its size and brightness rivals many Messier galaxies in the Coma–Virgo Cluster.

Again (and I never get tired of repeating this), despite popular belief, the famous Messier catalogue is not a list of the “brightest and best” deep-sky objects for small telescopes. It is a catalogue of objects compiled by the eighteenthcentury French comet hunter Charles Messier (he did not discover many of these objects), who believed they could be confused with comets “just beginning to shine.” Like Hidden Treasures, the Secret Deep list is an extension of the Messier catalogue – a deep-sky list for the twenty-first-century observer. In fact, two Secret Deep objects could very well be considered true Messier objects: Messier mentions NGC 5195 (Secret Deep 67) in his description of M51 but does not give it an individual listing. And there's an argument that NGC 3953 (Secret Deep 48) is actually M109.

HOW THE 109 SECRET DEEP OBJECTS WERE SELECTED

The purpose of this book is simple. It's designed to help you continue to explore the infinite wonders that populate the starry heavens and enrich your observing experience. As with my Hidden Treasures list, it would be wrong to call any of the Secret Deep objects “the best,” because what's “best” is highly subjective. (What one person claims is “the best” others might not agree.) It would be fair to say that the 109 selections in the Secret Deep are all deep-sky splendors worthy of your attention.

The Secret Deep list is actually an extension of the Hidden Treasures list. Both were created, in part, by the collective “you.” While researching Hidden Treasures, I came up with more than enough objects to fill the table. The “remainder” then became the foundation of a new list of 109 objects that I decided to call “The Secret Deep.” That new list expanded after I completed my Herschel 400 Observing Guide (Cambridge University Press, 2007), which alerted me to some fascinating deep-sky objects I hadn't previously encountered. Once I received my new telescope, I began to re-observe all these objects with a fresh eye.

With that telescope, I also resurveyed the night sky, constellation by constellation, for other bright or interesting objects that would be visible to amateurs living in the Northern Hemisphere – ones not already listed in the Messier, Caldwell, and Hidden Treasures catalogues. When the list grew to more than 200 objects, I decided to whittle it down. I did so, in part, by comparing my findings against those in the popular deep-sky object lists published by the following astronomical societies:

^ “Herschel 400”: Ancient City Astronomy

Club (St. Augustine, Florida)

^ “Additional Objects”: Hawaiian

Astronomical Society

^ “Best Objects in the New General Catalog”: A. J. Crayon and Steve Coe, Saguaro Astronomy Club (Phoenix, Arizona)

^ “Finest N.G.C. Objects”: Alan Dyer, Royal

Astronomical Society of Canada ^ “TAAS 200”: The Albuquerque

Astronomical Society (New Mexico)

As you can see in Appendix C, 51 percent of the Secret Deep objects appear in these other lists: this is remarkable given that, unlike the Secret Deep list, many of these lists include objects only in the NGC; they also include objects in the Messier, Caldwell, and Hidden Treasures catalogues! The Secret Deep list contains 97 NGC objects, and fully 75 percent of these appear in the other lists.

The final 109 Secret Deep objects comprise 38 galaxies, 23 open star clusters, 18 planetary nebulae, 15 bright nebulae (some with clusters embedded in them), 11 globular star clusters, 1 supernova remnant, 1 asterism, 1 quasar, and 1 black hole (the visible companion star). The table compares the number and types of deepsky objects covered in all four catalogues.

Owners of all four titles in the Deep-Sky Companions series will have the most up-to-date astrophysical and visual information on 436 deep-sky objects, with ancillary data on many more. And since the astrophysical, visual, and tabular data in The Secret Deep have been gleaned from many of the same sources in the other three volumes, you can compare the data with confidence. No other series of books to my knowledge offers observers such consistent data.

Object comparison table

The Secret Deep list has many superlative and fascinating objects. These include a planetary nebula whose last thermal pulse has produced a circumstellar shell similar to the one expected in the final days of our Sun's life, a piece of the only supernova remnant known that's visible to the unaided eye, the flattest galaxy known, the largest edge-on galaxy in the heavens, the brightest quasar, and the companion star to one of the first black hole candidates ever discovered.

And there's much more. Several of the open clusters are not only double but also possible binary clusters, being physically related. Some of the nebulae (vast swaths of dust and vapor) form fanciful shapes (a flying fox, cosmic rosebud, and fossil footprint, for instance). Many of these clouds of nascent matter harbor new stars and those still in the process of formation. There's also an abundance of globular star clusters. These ancient stellar “cities,” which populate the outskirts of our Galactic disk and halo, contain tens to hundreds of thousands of suns. Held together by the fantastic bond of gravity, these stellar congregations may be as old as the universe itself.

You'll also find many starburst galaxies (extragalactic systems that can manufacture suns at the phenomenal rate of hundreds of millions per year), cannibalistic galaxies (those consuming their dwarf neighbors), interacting pairs of galaxies, and grand-design spiral systems with supermassive black holes at the center of their active galactic nuclei.

In Chapter 1, “About this book,” I discuss the telescopes I used to observe the Secret Deep objects, my observing site and methods, helpful observing hints, and more. Since the history, astrophysics, and visual descriptions of many of these objects have never been described at length in any other popular work, this chapter also explains my approach to presenting the information.

I detail the 109 Secret Deep objects in Chapter 2. In many cases the essays describe recent observations from the Hubble Space Telescope, the world's largest ground-based telescopes, and a fleet of spacecraft that now peer (or have peered) into the universe with X-ray and infraredsensitive “eyes.” The essays are also flush with historical anecdotes and some have a dash of mystery (such as whether NGC 3953 is the real M109, and whether NGC 5195 should become the mysterious M102). Those interested in the history of astronomy will not be disappointed. The Secret Deep list includes objects discovered by many great astronomers from the eighteenth, nineteenth, and twentieth centuries, including William and John Herschel, but also Per Collinder, James Dunlop, Williamina Paton Fleming, Beverly T. Lynds, Albert Marth, Lord Rosse, E^´ douard Jean-Marie Stephan, Ju¨ rgen Stock, Wilhelm Tempel, and others.

Since some of the objects will present a visual challenge, especially to novice observers, I try to help as much as possible in the related essays by offering tips on how best to succeed in your search. It's also important to note that some of the nebulae in the list may appear quite small to visual observers, but they transform into magnificent cloudscapes in CCD images. In fact, this is the first book in the DeepSky Companions series that considers the astro-imager, whose efforts in the field I appreciate just as much as I do those employing the eye alone. Just take a moment to scan the gorgeous images of each Deep Sky object as captured by Mario Motta, whose work is featured in the book (see also Chapter 1). The details are stunning, the framing, exquisite.

Several appendices complete the work. Appendix A tabulates each Secret Deep object's position, constellation, type, apparent magnitude, and angular size. Appendix B does the same for the 20 additional Secret Deep objects. Appendix C is a table that lists each Secret Deep object and shows which astronomical societies considered it be one of the finest in the night sky. Appendix D is a list of photo credits, and at the end of the book is a Secret Deep checklist – a place for you to make personal notations on each object you find; it includes spaces for you to write down important information, such as the date observed, your location, the telescope and magnification used, atmospheric seeing and transparency, and any other special notes you want to record. It is a personal log that you can return to weeks, months, or years, later to see how you are progressing as an observer.

Deep-Sky Companions: The Secret Deep is not only a valuable resource or companion volume; it is your companion to take with you under the stars. I want the words to speak to you as you search, as if I were there to help guide you. It's difficult in our hobby sometimes to be alone under the stars. I want you to know that you are not; I am there with you in spirit. We all share a common bond – a love for the night. Not only do I want to encourage you to observe, to push yourself to new limits, but to enjoy a shared camaraderie. As I often tell my wife, Donna, when we are apart traveling, “No matter how many miles separate us, we can still share the sky.”

I've written each essay so that you can not only enjoy your time with it under the stars, but also in the daytime, or on those cloudy nights. I hope you enjoy reading the histories and science of these glorious objects. We have come so far in our knowledge of the night and the things we seek out with our “star ships.” I want to share with you that realized wonder.

I would like to thank Vince Higgs, Lindsay Barnes, Caroline Brown, and the editorial staff at Cambridge University Press for their encouragement, help, and support in this book and the Deep-Sky Companions series. I applaud Al and David Nagler of Tele Vue Optics in Chester, New York, for making such superb refracting telescopes that help me to dive deep into the visible universe.

I give special thanks to my longtime friend Mario Motta for taking the time to create the wonderful images of the Secret Deep objects he imaged with his 32-inch reflector – a part of his home! I thank Harvard astronomer and historian Owen Gingerich for looking over the interesting histories of some of the deep-sky objects whose discoveries have ties to Harvard College Observatory.

I thank my friend and colleague Larry Mitchell of Houston, Texas, for supplying me with William Herschel's original notes, which he drew from his original catalogues as they appeared in the Philosophical Transactions of the Royal Society of London; your kindness has been invaluable. Thank you to Terry Moseley, John M. Farland, and Wolfgang Steinicke for their help with Lord Rosse's discovery of NGC 3165. And a big bow goes out to the large pool of professional astronomers (many of whom are listed as the authors or principal investigators of professional papers on the objects being discussed) who took the time to look over the science presented in this book; you've enriched the text so much with your words and wisdom. Of course, if any errors have crept their way into this book, I'm responsible.

Finally, I would like to express my love for my beautiful wife, Donna, and Daisy Duke, our loving papillon, for standing beside me on this long journey; I thank you for your love, support, and understanding.

Well, it's time for you to go forth under the stars, pick away at the Secret Deep, and savor each galactic and extragalactic treat. Good luck.

I have been stargazing for nearly half a century. But I have yet to see all the sky's bright telescopic wonders. I don't mind. I'm in no rush. Unlike time and tide, the deep-sky objects we seek seem to hang around and wait for us to care. I suspect we all care. But I also understand that the task of seeking out these wonders without some guidance can be overwhelming. I felt that way recently when I forgot my star atlas on one very clear night. The stars shined down in magnificent splendor, the Milky Way appeared rich and pure, a marvel to behold. But I also felt a sense of loss, in that, without an atlas in hand, I didn't know where to point my telescope to find new wonders. The fact is, when it comes to taking any journey, guidance helps.

That's why I write these books. By sharing with you lists of celestial objects that have inspired me over the years, I hope to chart a course for you through the stars, to help you see its deep-sky splendors and enrich your time under the night sky. Besides, half the fun of any journey is sharing what we've learned along the way. This book is my latest message to you about yet another “romp” through the heavens and the wonders I have seen.

As silent as the sky may appear, it has a voice. It's the inner voice we listen to each time we look through our telescopes. It cheers us on during the excitement of the search, and celebrates with us each time we find a new target. It influences our thoughts and inspires emotion. It adds significance to our nights and makes us

Johann Wolfgang von Goethe (1749–1832)

yearn for more. If anything, in the DeepSky Companions series, I've tried to use my inner voice, to inspire you to find your own teller of secrets, so that you too can share the joy of astronomy with others. It's how we grow both personally and spiritually.

The Secret Deep objects are a rich assortment of visual and photographic gems that can add depth to your observing experience. They're all relatively bright, some more obvious than others, with a sprinkling of visual challenges. Admittedly, beyond the bright and obvious Messier objects, we have to search for fainter and less conspicuous wonders, but wonders nevertheless. Besides, I'd argue that many of the faint fuzzy objects we like to seek

require half eyesight and half imagination to “see.” I'm not talking about the “bad” imagination – the one that leads us to see things that don't exist – but the good imagination that fires up that special background knowledge of what we're actually looking at.

That's why the CCD images that Mario Motta took of these objects are so special. They help add a visual perspective not attainable in that type of detail with the eyes alone. It's like being in an art gallery looking at Van Gogh's Starry Night and trying to see beyond the canvas, into the creator's mind. In our quest, we satisfy our visual appetites by not only looking at CCD images, but also reading about the history and physics of each object. Indeed, many of these objects have been studied with large ground-based and space telescopes in all wavelengths of light. So we have a lot to ponder as we look through our telescopes. It's an exciting time to be an amateur astronomer. We have at our fingertips greater insight into the nature of the universe than ever before. This book, like its companions, will help you to see how astronomers have peeled back the onion layers of understanding over the years to give you the best and present knowledge of each wonder.

THE TELESCOPE AND SITE

There has been a change. The Tele Vue 4-inch f/5 Genesis refractor I used to observe all the objects in the three preceding Deep-Sky Companions series of books, as well as my Herschel 400 Observing Guide, is no longer in my possession. I loved (and still do love) that scope. It had been my observing partner for 13 years. But in 2007, Tele Vue founder Al Nagler and I had one of those eerie, simultaneous light-bulb moments. I felt it was time for me to graduate to a slightly larger telescope; at the same time, I wanted to somehow pass on my observing “torch” (the Genesis) to another observer. When we talked, Al not only understood, but he had already thought of the solution.

It turned out that he was considering donating his prototype of the 13-mm Nagler ultrawide eyepiece to the Springfield Telescope Makers, the amateur astronomy and telescope-making club that sponsors the annual Stellafane convention on Breezy Hill, Vermont. Al suggested we unite the Genesis refractor (with an autographed tube, and the accessories I used including three eyepieces (22-mm Panoptic eyepiece, and 7- and 4.8-mm Nagler eyepieces), 2-inch star-diagonal (with a 1¼-inch adapter),

• 1.8^ Barlow, Tele Vue Qwik-Point finder, and original carrying case) and his prototype 13-mm Nagler, and jointly auction them off on eBay. The proceeds from the sale, he said, would be donated to the Stellafane convention to help defray the cost of Stellafane's recently completed Flanders Pavilion.

Al's thinking was most appropriate: The Stellafane convention, whose roots date to the 1920s, inspired a revolution in amateur telescope making; Al's 13-mm Nagler inspired a renaissance in deep-sky observing that began in the 1980s and continues to this day; and Tele Vue's Genesis refractor has been referred to as “the catalyst for todays growing popular 4-inch APO market.” The auction closed on August 17, the Genesis refractor and Al's historic eyepiece have found a new home, and the money earned was donated to Stellafane.

What I now have in my possession is a beautiful Tele Vue NP-127 Nagler-Petzval 5-inch (660-mm) f/5.2 apochromatic refractor with a redesigned four-element optical system that offers me not only crisp wide-fields of view with 2-inch eyepieces, but also high-power capability with 1¼-inch eyepieces. And by high power, I mean, at times, I have pushed the instrument to its extreme: 100^ per inch of aperture, especially with planetary nebulae. Note that, throughout Chapter 2, I generally refer to this telescope simply as “the 5-inch.”

My arsenal of eyepieces consists of four workhorses: a Tele Vue 20-mm Nagler type 5 (33^), Nagler 11-mm type 6 (60^), Nagler 7-mm type 6 (94^), and Nagler 2– 4-mm zoom (330^–165^). I also have a Tele Vue 3^ Barlow, which offers me more magnification options up to 990^; as a rule, I generally go no higher than 495^, but I must admit that,

All the observations for this book were from my front yard in Volcano, Hawaii, which is at an altitude of 3,500 feet (1,100 m). I used to observe near the summit of Kilauea volcano in Hawaii's Volcanoes National Park, but something dramatic changed the environment and the landscape: On March 19, 2008, after I had finished my observations for the Hidden Treasures and Herschel 400 Observing Guide, Kilauea had its first summit explosion since 1924.

Since then, large swaths of the volcanic caldera have been off-limits, and dust and ash remain a problem there to this day; the summit eruption continues to enlargen a new vent inside Halemaumau crater, which also contains a glowing lava lake. So, while viewing the volcano is an awesome sight at night, it can also be less than ideal for looking at the stars on some “bad air” days (see the photo at the opening of this chapter).

Once I began observing at home, I actually found the “journey” very peaceful. I didn't have to drive anywhere, contend with car headlights in the Park, or the issues of volcanic smog (vog) and particle fallout – though now our home sits between two erupting vents and the vog conditions can be a problem here when the winds shift. The photo below shows vog over the town of Volcano at night from the “second” erupting vent, called P'u O'o.

Another benefit of observing from home was that I no longer had to “migrate” to avoid the ins and outs of the island's whimsical clouds or of curious passersby. No. If the clouds rolled in, all I had to do now was sit back in a chair, take a sip of hot chocolate, look up at the sky in the comfort ofmy home, and wait. Besides, although the telescope I have today is only 1 inch wider in aperture than my Genesis, it's a little bit heavier (perhaps Al thought I needed more exercise). But seriously, the night sky as seen from my house is no different than that up on the volcano's summit, which is just a few miles away. I can see the zodiacal light and band, as well as the gegenschein, from my home. I also get to run inside whenever something wonderful is out, so Ican share it with Donna. It's been a wonderful and calming experience, working on this book, and I appreciate the sky I have.

In addition to the Tele Vue 5-inch, I also used 10 ^ 50 Meade binoculars, and, on occasion, a nineteenth-century brass telescope made by Ross of London, which I simply refer to as “the antique telescope” in Chapter 2. It's the same antique telescope I used to observe some of the Hidden Treasures. The tube measures 17⅛ inches when open, and 7¼ inches when closed. The 1¾-inch objective is in excellent condition.

HOW TO USE THIS BOOK

To find a Secret Deep object, first locate its position on the wide-field finder chart that opens each entry. The chart not only gives you a wide-field view of the constellation it's in, but marks the location of the object relative to bright nearby stars (those with Greek letters or Flamsteed numbers). Next, locate those stars on the detailed finder chart that accompanies the object's photograph and text. Both the wide-field finder charts and the detailed finder charts are oriented with north up and east to the left. Finally, find the part of the text that describes how to locate the object and simply follow the directions.

After the full-page wide-field finder chart, each object's entry in Chapter 2 opens with an image of the object (oriented with north up and east to the left, unless otherwise noted) and a table of essential data: Secret Deep number; common name(s), if any; object type; constellation; equinox 2000.0 coordinates; apparent magnitude; angular size or dimensions; surface brightness in magnitudes per square arcminute (for most objects) and a personal rating of the object's ease of visibility from 1 (difficult) to 5 (easy); distance; and the object's discoverer and discovery date.

Note that you don't have to use the charts in this book. Since I provide the object's equinox 2000.0 coordinates, you can instead employ your favorite detailed sky atlas (such as Wil Tirion's Sky Atlas 2000.0) to locate the object. The choice is yours. The charts I created have a simple design. I've tried not to clutter them up with unnecessary details. They are designed to help you make the simplest and fastest sweep to each object, based on my personal experience. You might think otherwise, and I encourage you to pursue whatever venue you find suitable to your needs. Otherwise, my charts should be easy to read and simple to use.

Below the table you'll find William Herschel's original published description of the object, or, if William did not observe the object, his son John's. If neither observer discovered or observed the object, that section is blank. Larry Mitchell, a member of the Houston Astronomical Society, supplied me with William's original notes, which he drew from his original catalogues as they appeared in the Philosophical Transactions of the Royal Society of London.

Most of the John Herschel quotations have been gleaned from those given by the “Deepsky Observer's Companion” (www.fortunecity.com/roswell/borley/49/), which was created by the Astronomical Society of South Africa to promote its Deepsky Observing section. The quotes are from John Herschel's original observations, published in 1847 as “results of Astronomical Observations made during the years 1834, 5, 6, 7 [and] 8, at the Cape of Good Hope; Being the completion of a telescopic survey of the whole surface of the visible heavens, commenced in 1825.” During his stay in South Africa, John Herschel often made several observations of each object. The quotes used in this book's tables, however, refer only to his first observation; a date is given only if the junior Herschel discovered the object. At the end of each Herschel description is a code contained in parentheses (“H VIII-88,” for instance, or “h 2327”). These codes date to a classification system created and used by the Herschels. “H” stands for the elder Herschel and “h” for his son.

The Roman numeral in William Herschel's system identifies the class into which the elder Herschel placed each object:

I. Bright nebulae

• II. Faint nebulae

• III. Very faint nebulae

• IV. Planetary nebulae: Stars with burs, with milky chevelure, with short rays, remarkable shapes, etc.

• V. Very large nebulae

• VI. Very compressed and rich clusters of stars

• VII. Pretty much compressed clusters

of large or small stars

• VIII. Coarsely scattered clusters of stars

The Arabic numeral that follows is simply the order in which that object appears in that class. So H I-156 is the 156th object in Herschel Class I (bright nebulae).

The original 1888 New General Catalogue (NGC) description, or a description from the supplemental Index Catalogues (IC), follows each Herschel entry (if any). If the object is not from one or the other of these catalogues, it is left blank.

The Herschel and NGC/IC catalogue descriptions are followed by the running text, which may not only enhance the historical entries mentioned above but also bring to light any recent research findings. I then begin to describe the object's appearance in the sky, starting with its location and how best to find it. The directions are followed by my visual impressions as seen through the 5-inch at various magnifications. At times, I record its naked-eye or binocular appearance, or the view through my antique telescope; ocasionally I include descriptions by other observers using larger instruments. There may also be a visual challenge or two, as well as a brief visual impression of any other interesting objects nearby.

A drawing of the object as seen through the 5-inch at various magnifications also accompanies the text, so you can compare your view of any Secret Deep object with my own. The views may be very dissimilar, but that's okay; we all see things differently.

SOURCES OF DATA AND INFORMATION The data and information in this book were drawn from a variety of modern sources.

Many of these sources were used in DeepSky Companions: The Messier Objects, DeepSky Companions: The Caldwell Objects, and Deep-Sky Companions: Hidden Treasures, so you can compare the properties of these objects with confidence. Generally speaking, I gleaned recent research findings on the physical nature of each object from the Astronomical Journal or the Astrophysical Journal, and citations are given. From each object's apparent diameter and distance I calculated its physical dimensions using the formulas that appear on page 35 of DeepSky Companions: The Messier Objects. Other information, such as constellation lore; prop-ertiesofstars;andobjects'positions,apparent magnitudes, angular sizes, and surface brightnesses, come from the following excellent sources (primary sources are listed first).

Star names, constellations,

and mythology

Allen, Richard Hinckley. Star Names: Their Lore and Meaning. New York: Dover Publications, 1963.

Ridpath, Ian. Star Tales. New York: Universe Books, 1988. See also www. ianridpath.com/startales/contents.htm.

Staal, Julius D. W. The New Patterns in the Sky: Myths and Legends of the Stars. Blacksburg, VA: McDonald and Woodward, 1988.

Stellar magnitudes and spectra

Stars, http://stars.astro.illinois.edu/sow/ sowlist.html.

Hirshfeld, Alan, Roger W. Sinnott, and Francois Ochsenbein, eds. Sky Catalogue 2000.0, Vol. 1, 2nd edn. Cambridge, UK: Cambridge University Press, and Cambridge, MA, USA: Sky Publishing Corp., 1991.

Stellar data

Stars, http://stars.astro.illinois.edu/sow/ sowlist.html.

ESA. The Hipparcos and Tycho Catalogues. Noordwijk, the Netherlands: European Space Agency, 1997.

Double stars

Luginbuhl, Christian B., and Brian A. Skiff. Observing Handbook and Catalogue of Deep-Sky Objects. Cambridge, UK: Cambridge University Press, 1989.

USNO. The Washington Double Star Catalog. Washington, DC: Astrometry Department, U.S. Naval Observatory. http: /ad.usno. navy.mil/ad/wds/wds.html.

Variable stars

American Association of Variable Star

Observers, www.aavso.org.

Open star clusters

Archinal, Brent A., and Steven J. Hynes.

Star Clusters. Richmond, VA: Willmann-Bell, Inc., 2000.

Open star cluster distances generally were gleaned from the professional literature.

Globular star clusters

Harris, William E. Catalog of Parameters for Milky Way Globular Clusters. Hamilton, ON: McMaster University. www.physics.mcmaster.ca/~harris/ mwgc.dat.

Skiff, Brian A. “Observational Data for Galactic Globular Clusters.” Webb Society Quarterly Journal 99:7 (1995), updated May 2, 1999.

Globular star cluster distances generally were gleaned from the professional literature.

Planetary nebulae

Skiff, Brian A. “Precise Positions for the NGC/IC Planetary Nebulae.” Webb Society Quarterly Journal 105:15 (1996). (Positions.)

Luginbuhl, Christian B., and Brian A. Skiff. Observing Handbook and Catalogue of Deep-Sky Objects. (Dimensions and central star magnitudes.)

Cragin, Murray, James Lucyk, and Barry Rappaport. The Deep-Sky Field Guide to Uranometria 2000.0, 1st edn. Richmond, VA: Willmann-Bell, Inc., 1993.

Planetary-nebula distances generally were gleaned from the professional literature or from the World Wide Web page of the Space Telescope Science Institute (www.stsci.edu).

Diffuse nebulae

Cragin, Murray, James Lucyk, and Barry Rappaport. The Deep-Sky Field Guide to Uranometria 2000.0, 1st edn.

Diffuse nebula distances were gleaned from the professional literature.

Galaxies

The Deep-Sky Field Guide to Uranometria 2000.0, 1st edn. (Positions, angular size, apparent magnitude, and surface brightness.)

NASA. The Extragalactic Database. Pasadena, CA: Infrared Processing and Analysis Center. http://nedwww.ipac.caltech.edu/. (Types, mean distance, radial velocity, and all detailed descriptions of galaxy structures as seen in photographs have been gleaned from the accompanying notes.)

Tully, R., Brent. Nearby Galaxies Catalog. Cambridge, UK: Cambridge University Press, 1988. (Inclination, total mass, and total luminosity.)

Extragalactic supernovae

List of Supernovae. Cambridge, MA: Central Bureau for Astronomical Telegrams. http: /cfa-www.harvard.edu/iau/lists/ Supernovae.html.

Other details of discovery were gleaned from individual IAU Circulars.

Historical objects

Smyth, Captain William Henry. A Cycle of

Celestial Objects. Richmond, VA: Willmann-Bell, Inc., 1986.

Glyn Jones, Kenneth. The Search for the Nebulae. Chalfont St Giles, UK: Alpha Academic, 1975.

Other historical anecdotes in this book were gleaned from various individual and professional papers from the nineteenth and early twentieth centuries.

General notes

Note that the World Wide Web Uniform Reference Locators, or URLs, are subject to change. The dimensions, magnitudes, and positions of all other additional deepsky objects in this book were taken from The Deep-Sky Field Guide to Uranometria 2000.0.

As in the other books in the Deep-Sky Companions series, the data in this book differ from those appearing in older but popular references. This book contains the most up-to-date astronomical data and accurate historical and observational information about each object in the Secret Deep catalogue that you'll find in any book in the popular literature.

THE FINDER CHARTS

As I previously mentioned, the wide-field and detailed star charts in Chapter 2 are of my own design. The Secret Deep number

Secret Deep 8 (NGC 1084)

and proper name of each object appears at the top of the chart. The maps appear with north up and east to the left.

The purpose of the wide-field finder charts is simply to show you the brightest constellations or star fields around the Secret Deep object. Each shows stars roughly to magnitude 4 or 5, and sometimes 6 (but generally only in the region near the Secret Deep object, and only if I feel they will help in the naked-eye or binocular search. Faint stars are more prevalent if the constellation is dim, like Sculptor.

In creating these charts my philosophy was to simplify the view, to help you focus on your target by removing peripheral noise. The purpose of these charts is to help you hone in on one object and one object only, and I've done the field work to help you get there in the fastest and most efficient way possible. Why clutter the view, I reasoned, with lots of dim stars and other objects when all you want to do is see the target you're after. As the old saying goes, “Obstacles are what you see when you take your eye from the goal.”

To help you in your search, I've traced out the “stick figure” form of the main constellations in the view. I've also labeled them and their brightest stars, using the traditional Bayer (Greek) letters or Flamsteed numbers. Sometimes I've included a popular star name, such as Mira, the well-known winking star in Cetus the Whale. But in special cases, you may find a non-traditional, italicized, lower-case letter, such as an a or b; these are additional unnamed or numbered guide stars, which you'll find in the text described as Star a or Star b, etc. One symbol, a circle, is used to mark the location of each Secret Deep object on these wide charts.

The detailed finder charts have the same orientation as the wide-field charts, but they show a much smaller area of sky in more detail. The constellation name is given as are any boundary lines. A scale bar appears at the bottom of each chart. Stars are shown to magnitude 11 near the target; sometimes, fainter stars are shown, if I feel they'll help you to identify it. In the detailed charts, I've labeled each Secret Deep target with its full proper name (such as NGC 1084) in black. A faint gray symbol is used to mark the location of other interesting deep-sky objects nearby, which are labeled (also in gray) with the NGC prefix omited. Note too that, in these charts, the italicized letters may also refer to an asterism (a triangle, arc, pair of stars, or line), as described in the text.

I use the traditional symbols below to represent the different classes of deep-sky objects. In the case of galaxies, I also show their apparent orientations.

Thus, to find a Secret Deep object, first locate the object's position on the wide-field finder chart. Next, note the brightest star near the object and locate it on the detailed finder chart. Now, read the accompanying text on how to locate the object and simply follow the directions.

THE IMAGES

All the object images in this book are reproduced in black and white, with north up and east to the left. Unless otherwise noted, all were taken by my longtime friend and colleague Mario Motta with an STL 1001E SBIG camera on his homemade 32-inch telescope. It has a field measuring 17⁰ ^ 17⁰ . Photos of objects larger than 17 arcminutes were taken with Motta's 6-inch F/9 Ritchey–Chre´tien astrograph, which has a1^{^} field. (Detailed credits for these and additional photos appear in Appendix D.) I took some of the wider shots, such as Orion's Belt and other large deep-sky objects. I've also reproduced images from the HubbleSpaceTelescopeandotherlargetele-scopes. These images were used for the sole purpose of inspiring you to use your imagination. You certainly will not see anything like these images when you look through your telescope, but how else can you fully appreciate what it is you are seeing? So do not be discouraged, be enlightened.

Mario Motta and his 32-inch dreamscope

Astrophotographer and longtime amateur astronomer Mario Motta wears many hats. By day, he's a renowned cardiologist in Salem, Massachusetts. He served as the President of the Massachusetts Medical Society from 2009 to 2010, is a member of the American Medical Association's New England Delegation, serves as an AMA delegate from Massachusetts, was elected to serve on the AMA Council of Science and Public Health, and holds an academic appointment as Associate Professor of Medicine at Tufts Medical School, among other things. By night he's an extraordinary amateur astronomer and dark-sky advocate.

An advanced amateur astronomer, Mario has built several observatories and telescopes. His Wingaersheek Observatory – which sits atop his study in his home in Gloucester, Massachusetts – houses his homemade 32-inch reflector under a 20-foot dome that overlooks Ipswich Bay to the north and a large salt-water marsh to the south. These calm bodies of water help to produce great local atmospheric seeing conditions; they also help to keep his skies reasonably dark. A member of the International Dark Sky Association and the local New England Light Pollution Group, Mario has been, and continues to be, an avid promoter/protector of dark skies: Thinking globally and acting locally, Mario spearheaded a successful lighting ordinance to further protect the night sky over his town.

Mario is quick to tell you, however, that it was his charming wife, Joyce Motta, a lawyer by profession and an artist/photog-rapher by avocation, who was responsible for finding this astronomer's paradise, which also doubles as a quiet reserve for Joyce's artistic and photographic endeavors.

One of the largest telescopes in New England, Mario's Monster (as I congenially call it) is a state-of-the-art, robotic telescope that weighs 1,200 pounds and sports a special optical system of the relay design. It was the brainchild of Mario, his optical-designer friend Scott Milligan, and other members of the Amateur Telescope Makers of Boston (ATMOB), of which Mario has been a longtime member and past president. It is this same telescope that Mario used to take the images in this book.

Mario's telescope is an all-spherical, multi-element, relay design – an improved optical system of the one pioneered by Donald Dilworth a quarter century ago and displayed at the annual Stellafane telescopemakers convention in Vermont. This new system (which ameliorates chromatic aberration effects and extends the sharp imagery in the telescope's off-axis performance), provides “significant advantages,” Mario says, over a conventional Newtonian, Cassegrain, or Dall–Kirkham telescope.

The new design incorporates a 32-inch f/3 spherical primary mirror, a 7.8-inch Mangin spherical secondary mirror (with a flat back end), and 3.8-inch spherical corrector lenses. The main advantage of the scope is the smooth, highly accurate, fully coated, spherical optical surfaces. The double pass through the front surface removes the spherical aberration of the primary mirror.

“The converging beam then comes to a focus back down the central axis,” Mario explains, “allowing for a natural field stop for much greater contrast and enhancement than that in conventional telescopes.” This converged beam is then passed through an all-spherical doublet, then two separate spherical lenses. “These lenses both collimate the beam for refocusing back behind the primary,” he says, “and also remove the color aberrations of the system.” The light finally passes through a central 5-inch perforation in the primary mirror, and comes to a focus 11 inches behind it, offering sharp, high-contrast images.

When I first met Mario, I was a 14-year-old “apparition” haunting the halls of Harvard College Observatory, in Cambridge, Massachusetts, where I had been given permission to use the Observatory's 9- and 15-inch refractors to study the stars and planets. Mario was there because the ATMOB held its monthly meetings at

the Observatory's Phillips Auditorium, and its members used the 9-inch refractor on clear nights after the meetings. It didn't take long before Mario and other friendly faces invited me to join them. They also persuaded me to give a talk to the club about deep-sky observing – specifically on how to find Messier objects with my own 4½-inch reflector from the city.

Since I had never given a public talk before, I didn't know what to say or how to say it. So I rehearsed for weeks, trying to memorize a half-hour worth of words. When the big night arrived, I thought I was ready. But as soon as I faced the audience, my body seized up. My throat tightened, my eyes widened. I began to sweat profusely. My heart thumped uncontrollably in my chest (Mario was probably ready to get his portable heart paddles). Everything I had planned to say was wrapped in a mental fog. I couldn't breath. When my mouth broke free, and my lips moved, nothing audible came out.

An eternity passed. I heard people in the room shuffling in their seats, some cleared their throats. Their eyes bored into mine. Then Mario asked me a simple question about a Messier object. After a moment of thought, calmness magically returned. I wasn't speaking to an audience anymore (at least not in my mind), I was speaking to Mario, and that made all the difference. I answered his question, then another, and another. The night didn't turn out so bad in the end.

After that, Mario and other ATMOB members took this “kid” under their wings. Their meetings were like being with family. We enjoyed not only nights at Harvard, but, over the years, many crisp nights under the stars at the club's dark-sky site and clubhouse. After I moved to Hawaii, Mario and I kept in touch. Occasionally he makes it out to the Rock, and occasionally I get to visit him on the East Coast. In fact, on a memorable Halloween night in 2009, I was a guest of Mario and Joyce. Mario and I stayed up almost until the dawn, visually observing deep-sky objects through his impressive 32-inch telescope. In fact, the first object we looked at was van den Berg 1 – the first object in the Secret Deep catalogue.

As former president of the ATMOB, Mario initiated a collaboration between public schools and the ATMOB, who now give over 50 star parties a year in the greater Boston area for school kids, and partner an amateur with a school district. Mario's interests have been in galactic evolution, gamma-ray bursters, supernovae, as well as variable stars. He also gives many talks on light pollution issues. In 2003 Mario received the Las Cumbres Award from the Astronomical Society of the Pacific for astronomical outreach, and in 2005 he received the Walter Scott Houston Award from the Astronomical League. I am honored to share with you the results of his latest passion: deep-sky imaging. Mario also wanted to share the following words with you.

I have enjoyed astronomy for as long as I can remember, starting as a young child. For a time, I strongly considered making astrophysics my career choice, but eventually ended up in medicine as a cardiologist. My love of astronomy, however, has never waned. I built my first telescope, an 8-inch Newtonian, as a teenager at age 14. I enjoyed that telescope, but always yearned for larger optics. As my appetite for large telescopes always exceeded my budget, I, through the years, continued to build larger and larger telescopes, always completely homemade. I bought an old lathe and milling machine and learned to make all the mechanical parts as well. I consider grinding the optics and manufacturing all of the mechanical parts not only a challenge and scientific pursuit, but also an art form.

I have built three home observatories through the years. My latest telescope and observatory, which was completed in 2006, is what I consider my ultimate dream telescope. A 32-inch f/6 relay telescope, it has the power to allow me to gaze deep into the universe, and the precision and accuracy to give me stunning views when I image. All of the images attributed to me in this book were taken from my home observatory with this telescope. It is an unusual design, an all-spherical optical design with 11 optical surfaces.

The primary mirror is 32 inches. It has 584 mechanical parts, all personally hand made. The final result is an instrument of beauty to behold and to use. I have the very good fortune of being married to a wonderful woman who allows part of her house to be an observatory. This house was built from the initial design to have an observatory as an integral part of the house, with a pier extending through two floors to reach the observatory. This allows me to observe the heavens any clear evening with little effort, the telescope always ready.

When my good friend and author of this book asked if I would be interested in obtaining the images I jumped at the chance. Steve O'Meara and I have a long-term friendship going back over many years, and what has always cemented our friendship is a mutual and deep love of observing the universe. This has created a deep bond that binds us despite the fact that we now live thousands of miles apart. Steve's books are always well written and highly informative, and thus it was an honor to be associated with this project. I hope all of the amateur astronomers who track down the objects in this book will get as much pleasure from observing or photographing them as I did.

THE DRAWINGS

All the sketches in Chapter 2 are composites of field drawings I made at various magnifications. They are shown with north up and east to the left. The orientation matches that of the corresponding photograph. Each Secret Deep object in the drawing is labeled with its proper name in the upper left corner, two field orientation labels (N for north and W for west), and a scale bar to help you size up each object in your own telescope.

The composites show details visible at low, medium, and high power. This is a technique I've employed for decades and enables me to share with you the overall grandeur of the object in one portrait. It's important to note, however, that I've boosted the contrast greatly for two reasons: (1) to hold the detail for reproduction, and (2) to enhance the beauty of the subtle

view. If I were to try and reproduce the delicate details of some deep-sky objects, you probably wouldn't recognize them, or see them for that matter, in the drawings, they would be too faint. In the text, I do break down what details I could see (and could not see) at different magnifications, so use the verbal description as your explanatory guide.

It's time now to go out and explore and give thought to the splendor of the universe.

Secret Deep 1

(van den Bergh 1)

vdb 1 is a little-known reflection nebula only about 30⁰ south-southeast of Beta (b) Cassiopeiae (Caph). It is also a dim reminder not only that little treasures can hide in the glare of brighter companions, but also that not all objects accessible to small- to moderate-sized backyard telescopes have associated with them a Messier, New General Catalogue (NGC), or Index Catalogue (IC) designation. In fact, this first object in the Secret Deep catalogue is also the first object in Sidney van den Bergh's catalogue of reflection nebulae, which was originally published in a 1966 Astronomical Journal (vol. 71, p. 990).

In his study, van den Bergh scanned Palomar Sky Survey prints in an attempt to identify reflection nebulosity associated with all Bonner Du¨ rchmusterung (BD) and Cordoba Du¨ rchmusterung (CD) stars – two of the most complete pre-photographic star catalogues covering the northern and southern celestial hemispheres, respectively. Of the 100,000 or so stars investigated to a declination of -33^{^} , he identified reflection nebulosity associated with about 500 of them.

In his catalogue, van den Bergh also included nebulae already found in similar surveys; vdB 1 was one such inclusion; it appears in Beverly T. Lynds Catalogue of Bright Nebulae (University of Arizona), first published in a 1965 Astrophysical Journal Supplement (vol. 12, p. 163). Like van den Bergh, Lynds encountered it in her scans of Palomar Sky Survey prints and listed it as the 578th object in her catalogue. Thus, vdB 1 is also known as Lynds' Bright Nebula 578 (LBN 578).¹

In his emulsions, van den Bergh noted that the nebula is both “very bright” and “very blue.” In modern color shots, it's a

5⁰ -long wash of cerulean light surrounding bright illuminating stars; the hue rivals the azure sheen of the Merope Nebula in the Pleiades star cluster (M45) in Taurus, though vdB 1's glow is set against a dusty carpet of multicolored stellar jewels in the Cassiopeia Milky Way.

Detecting vdB 1 is by no means difficult in a 5-inch refractor under a dark sky. The small, foggy glow is primarily illuminated by three roughly 9th-magnitude stars, which burn through the nebula like lights seen through afog.Ifindthenebulaaboutaschallengingto seeassomeofthesmallpatchesofnebulosity in the Pleiades. The night must be very transparent, because the slightest haze will cause all the stars in the region to appear nebulous.

But that's the key to identifying the nebula. You simply have to use low power and averted vision to compare the triad of 9th-magnitude stars embedded in the

nebula with stars of similar magnitude nearby. I found that once I carefully performed this exercise, vdB 1 appeared evermore prominent with time.

The nebula takes magnification surprisingly well. At 60^, for instance, the glow appears as a fuzzy wrap of uniform light with a slight teardrop shape toward the southwest, but this is an illusion, I'm sure, owing to the fact that that's where the pair of 9th-magnitude suns resides.

At 94^, the nebula is most apparent around the solitary 9th-magnitude sun at the northeast end of the triad. The triad also is joined by a roughly 11th-magnitude sun further to the northeast, making the asterism appear like a little Sagitta. To the northwest is an equally bright arc of three suns, the end stars of which are near equal double stars. The longer I look at this amazing little path of light, the more extended it appears, especially to the northwest and southeast of the solitary northern star in the triad.

Return to low power. If you can get a field of 2^{^} , all the better. Now, let your eye relax and view the entire field from Beta Cassiopeiae to vdB 1. Do you see anything curious? I can't recall how many times I have viewed this field at low power without ever having noticed the fact that vdB 1 lies on an island of stars surrounded by a large loop of dark nebulosity, LDN 1265, like the murky waters of a dark moat.

I didn't notice the dark nebula until December 11, 2009 – a night of unexpected clarity and transparency. That night, the low-power, wide-field view of vdB 1 looked, in my mind's eye, like an aerial view of city lights on a mist-laden island at night. The darkest part of LDN 1265 takes the shape of an upside down J; it begins near Beta Cassiopeiae and curls around vdB 1 to the southwest. It's been a while since I've been taken by surprise. The dark J is very bleak. Even at 60^ or 94^, I could not detect any starlight within it. It's worth a visual sail along those “dark waters.”

The field is even more amazing in wide-field images I've seen, which show the multifaceted nature of this nebulous region (both bright and dark) in remarkable detail. The large swath of LDN 1265 appears as a fat dusty crescent that seems to caress Caph at its northeastern tip – interesting, since Caph is from Kaff-al-Khadib, meaning “the stained hand.” Here's another interesting aside: this dark nebula is not shown on most popular atlases today. But I was happy to find it plotted (though not labeled) on Antonon Becvar's 1950 Atlas of the Heavens (also known as the Atlas Coeli).

In October 2009, I viewed vdB 1 from a dark-sky site just beyond Edmonton, Alberta, Canada. Larry Wood, of Edmonton, and Rick Huziak, of Saskatoon, offered me glimpses of this beautiful nebula through 12-inch f/6 and 10-inch f/5 reflectors, respectively. In both scopes, the nebula was an unmistakable glaze of white light surrounding the bright triad of 9th-magnitude stars. But unlike the view in my 5-inch, faint tendrils of light could be seen along the edges of the main nebulosity, giving the object the appearance of a wind-tattered flag. Both Larry and Rick agreed that this object would be perfect for the Secret Deep catalogue, especially since it's not difficult and would otherwise remain a deep-sky obscurity.

AN IMAGING CHALLENGE

If you look carefully at Mario Motta's beautiful image of vdB 1, you can see to the northeast an interesting loop structure associated with a nebulous star, as well as another nebulous star just 37⁰⁰ to the north: These stars (V633 Cassiopeiae (also known as LkHa 198) and V376 Cassiopeiae, respectively) are Herbig Ae/Be stars associated with extended reflection nebulosity. They lie some 1,900 light-years distant, about as close as the North America Nebula in Cygnus; the distance to vdB 1 in the table on page 18 assumes the Herbig–Haro object and it belong to the same molecular cloud complex, and thus have a similar distance.

Herbig Ae/Be stars are intermediatemass, pre-main sequence stars that share numerous spectroscopic and photometric properties with T Tauri stars – very young (<10 million years) stars found in reflection nebulae that are still undergoing gravitational contraction and often have large vestige accretion disks. But the exact nature of the Herbig Ae/Be circumstellar environment is quite complicated and uncertain. Many such intermediate-mass young stellar objects may be surrounded by large quantities of circumstellar material in a circumstellar disk, which may be still accreting onto the central star.

In high-resolution imaging, V633 Cassiopeiae appears to be a single star with an extended “loop-like” reflection nebula oriented northwest–southeast. The “loop” traces the redshifted lobe of a CO outflow, the driving force of which may be an infrared source 6⁰⁰ to the north ( V633 Cassiopeiae B (LkHa 198-B)). The loop also contains two Herbig–Haro objects: HH 161 and HH 161-B.

These objects – named after George Herbig (University of California, Berkeley) and Mexican astronomer Guillermo Haro, who discovered the first three such objects in 1946–7 in images of the nebula NGC 1999 in Orion (Hidden Treasure 33) – are small-scale shock regions intimately associated with star-forming regions. They're created when fast-moving jets of material ejected from very young stars collide with the interstellar medium. As the ejected flow plows into the surrounding gas, it generates strong shock waves, which move at speeds topping 100,000 miles per hour, exciting atoms along the way and causing the nebula to glow. All known Herbig– Haro objects have been found within the boundaries of dark clouds and are strong sources of infrared.

V 376 Cassiopeiae is equally intriguing. In a 1996 Astrophysical Journal (vol. 472, p. 349) Canadian astronomer Louis Asselin (ObservatoireduMontMeganticandDepart-ment of Physique, Montreal) announced that on the basis of seeing-limited images taken at the Canada–France–Hawaii Telescope atop Hawaii's Mauna Kea, V376 Cassiopeiae is seen close to edge-on with a possible circumstellar disk.

Kester W. Smith (Max-Planck-Institute for Radio Astronomy, Bonn) and his colleagues support that claim. In a 2004 Astronomy & Astrophysics, the astronomers report that speckle observations of V376 Cassiopeiae partially reveal that the inner regions of the system are in fact obscured by a flaring circumstellar disk or torus seen close to edge-on. A Hubble Space Telescope image also lends support. However, it suggests a nearly edge-on disk at a position angle of about 140^{^} ; the nearside of a bipolar outflow lobe can also be seen extending to the west. The observed light probably arises mostly from scattering from the inner edge of the outflow cavity or from the surface of a flared disk or circumstellar torus.

In October of 2008, Mario Motta and I viewed vdB 1 visually through Mario's 32-inch reflector. The 9th-magnitude stars dominated the view and the nebula nearly filled the field of view; it looked as if a cirrus cloud had moved in and destroyed the night's viewing. Unfortunately, we did not know at the time about the two nearby Herbig Ae/Be stars. It wasn't until Mario later imaged the field that he noted the mysterious loop of nebulosity nearby. That sent me on a search of the literature. Now I wonder how large an aperture is required to see the loop visually. Go out and give it a try!

ngc 134 is an extraordinary, nearly edge-on spiral galaxy in Sculptor, just 30⁰ east-southeast of 5th-magnitude Eta (Z) Sculptoris, or nearly 10^{^} (about a fist held at arm's length) south-southwest of NGC 253 (Caldwell 65), the more popular Silver Coin galaxy. In fact, in a sweeping view of the region, NGC 134 just happens to be surrounded by, and somewhat lost among, a cast of extragalactic prima donnas – including NGC 253, NGC 300 (Caldwell 70), and NGC 55 (Caldwell 72) – all of which are savagely beautiful when seen through small telescopes.

Nevertheless, NGC 134 is a treasure that's relatively easy to acquire. At a declination of -33^{^} 15⁰ , the object is only 1^{^} farther south than M7 in Scorpius. Of course, the galaxy's faintness makes it a challenge to find from mid-northern latitudes. But it's a stunning object when seen from the southern USA.

NGC 134's discovery is often attributed to John Herschel, but Herschel did note that it may be the 590th object listed by James Dunlop in his 1828 catalogue, which was published six years before Herschel arrived at the Cape of Good Hope and began surveying the southern heavens with his 18-inch f/13 speculum reflector. Of the new object Dunlop wrote: “A faint round nebula, about 2⁰ diameter.” Of course, while his position places the object near NGC 134, his description of it does not sound at all like this elliptical wonder, which is even apparent in the smallest of telescopes.

Herschel also sketched the galaxy, clearly showing its spindle-shape with tapering edges. He classified NGC 134 as an elliptical nebula “normal” in its character, meaning “as the condensation increases towards the middle, the ellipticity of the strata diminishes, or in which the interior and denser portions are obviously more nearly spherical than the exterior and rarer.” Of its nature, Herschel suggested that the “time is clearly arrived for attempting to form some conception at least of the possibility of such a system being either held in a state of permanent equilibrium, or of progressing through a series of regular and normal changes, resulting either in periodical restorations of a former state, or in some final consummation.”

Seen through small telescopes, wafer-thin NGC 134 appears to be a near twin of the spectacular edge-on galaxy NGC 4565 (Caldwell 38) in Coma Berenices.

Photographs, however, reveal the two galaxies to be worlds apart in appearance. NGC 4565 is a classic example of a nearly edge-on spiral galaxy with an oval hub surrounded by a large symmetrical disk of dust and starlight. Although NGC 134 is similarly oriented (~14^{^} from edge on), it is a different class of spiral. The innermost part of the disk is smooth out to about 50⁰⁰ . Multiple dust lanes that outline the arm fragments then begin at the rim of this smooth disk. Its bright, very small nucleus is partly hidden by a series of dark, feathery dust lanes that delineate the galaxy's clumpy, spiral arms (rich in starforming HII regions) that loosely wrap around a bright, bar-shaped central region. Dust-lane asymmetry between the near and far sides is particularly strong.

Deep exposures have also revealed plumes streaming off the galaxy's major axis in both directions – like the flagella of some extraterrestrial euglena. Indeed, as Mario's image on page 23 shows, the galaxy's disk appears warped, resembling a bent vinyl LP left out too long in the burning sun. Such warps are not unusual; our Milky Way, for instance, has a small one, and they are found on many other galaxies that have an interacting companion. It's possible that a smaller galaxy has gravitationally stretched matter from NGC 134, forming the plumes (and the warp). One likely candidate would seem to be 13th-magnitude NGC 131, which lies only 5⁰ west of NGC 134, but this galaxy does not seem to be involved; a still fainter galaxy, ESO 350-G21, may be the disturbing culprit. It's also possible that a smaller galaxy collided with NGC 134 in the past, causing the visible disruption. The answer still eludes astronomers.

From our perspective, NGC 134 lies in a haystack of galaxies, centered on the impressive Sculptor Group, which lies at a distance of 10 million light-years, and is the nearest gathering to our own Local Group. But NGC 134 is not a true member of the Sculptor Group. R. Brent Tully (University of Hawaii) places it 62 million light-years from Earth in the Telescopium–Grus Cloud of galaxies. NGC 134 is a massive system

NGC 134
	NGC 131

with a diameter of about 150,000 light-years, making it as large as NGC 4565.

To find this southern wonder, use the chart on page 22 to locate 4th-magnitude Alpha (a) Sculptoris, which is some 12^{^} southsoutheast of Deneb Kaitos, or Beta (b) Ceti. Next, use binoculars to locate 5th-magnitude Eta (Z) Sculptoris about 7½^{^} southwest of Alpha Sculptoris. Now center your telescope on Eta Sculptoris and use the chart on this page to locate NGC 134, which will look like a 10th-magnitude needle of pale light 30⁰ to the east-southeast of that star.

The galaxy is visible from Hawaiian skies in 7 ^ 50 binoculars and in my antique telescope. At 33^ the galaxy sits atop a trapezoid of suns southeast of Eta. The galaxy is immediately noticeable as a white scratch between the trapezoid and other field stars that pen the galaxy in. Since the galaxy is nearly edge-on, its thin arms are less noticeable than the core, which requires averted vision to see at this magnification. With time, the galaxy's bright core swells in layers.

At 60^, the galaxy is a fine sight and seems to awaken the senses. The trapezoid is more of a square with a dim star within. The arms appear to favor each side of the nucleus along the major axis. The north side also seems to have a break near the faint star on its western side. At 94^, the galaxy looks more milky and feathery. The core is mottled, and the arms look like moist breath on string. The southern half of the galaxy is definitely brighter than the northern half. The southern arm is also knotted in a most delicate manner.

A 13th-magnitude star can be seen northnorthwest of the galaxy's nuclear region and could easily be mistaken for a supernova. A supernova was discovered in the galaxy in 2009: Stuart Parker, who lives in the small village of Oxford in New Zealand's South Island, discovered Supernova 2009gj on June 20, 2009, shining at magnitude 15.9 in his images of the galaxy, which he had taken through his Celestron 14 telescope.

Note that since NGC 134 is located about 60 millionlight-yearsaway,thelightweseefrom its disk through our telescopes left the galaxy around the time of the Cretaceous–Tertiary mass extinction of the dinosaurs on Earth.

ngc 488 is a small but beautiful spiral galaxy in the mysterious cord of Pisces – about 10^{^} west-northwest of Alpha (a) Piscium, the knot in the line that joins the two Fishes. I say mysterious because no one is quite sure why this cord exists, why the fishes have been united in this way. It may refer to the Roman myth in which Venus and Cupid (the goddess of love and her boy) startled the monster-dragon Typhon, who thrives in fire but fears water. To escape the beast's wrath, the pair tied themselves together with a long cord (so they would not be separated), then dove into the dark waters of the Euphrates, where they turned themselves into fishes. Today we see the successful escape commemorated in the sky as Pisces.

I first encountered NGC 488 in Burnham's Celestial Handbook (Dover Publications, New York, 1978), which spotlights the compact spiral simply in a photo. Still, the galaxy's fine weave of spiral arms, dappled with extragalactic filigree, was enough to entice wonder. Not until I moved to Hawaii in 1994, though, did I try to hunt it down. When I did, the view didn't disappoint me. But more on that later.

For now, just look at Mario Motta's marvelous image that opens this page. The disk has nearly perfect spiral structure, which we see 46^{^} from face-on. Astronomers refer to NGC 488 as the prototype multiple-armed spiral galaxy (more-evolved galaxies have thicker, more-open arms).² NGC 488's tightly wound spiral pattern reminds me of a Fourth-of-July whirligig, surrounded by bursts of foreground starlight and little extragalactic sparklers. Despite its small apparent size (5.5⁰ ^ 4.0⁰ ) the galaxy is a true astrophysical wonder, measuring 150,000 light-years across in true physical extent. It appears so small in the sky because we see its light 95 million light-years distant in the Cetus–Aries Cloud of galaxies. NGC 488's form consists of a large and smooth central bulge surrounded by a uniform arrangement of thin, stringy fragments. The tight spiral pattern can be traced across the entire face of the disk, though no fragments can be followed for more than about half a revolution. Each filament appears clumpy, though without prominent star-forming knots.

As German astronomer Burkhard Fuchs (University of Heidelberg) discusses in a 1997 Astronomy & Astrophysics (vol. 328, p. 43), the young galaxy has a prominent central bulge and an inner counter-rotating disk, both of which suggest that the bulge formed – not during the collapse of the protogalaxy or by secular evolution of the galactic disk – but by cannibalizing satellite galaxies. NGC 488's counter-rotating disk, for instance, can be interpreted as the debris of satellite galaxies that disintegrated while they merged with NGC 488.

Kinematic studies have been made of the stars in NGC 488's disk out to a radius of 65,000 light-years from the galaxy's bulge, at which point the stars travel at a velocity of 363 km/second – an astonishing rate given that our Sun orbits the Milky Way at a speed that's about 1.5 times slower! NGC 488 has, in fact, the largest rotational velocity known for any normal spiral galaxy.

These studies have also furthered the contention that the spiral appearance of galaxies represents areas of enhanced density (density waves). Compression waves rotate more slowly than the galaxy's stars and gas – like cars in a traffic jam. As gas enters a density wave, it gets squeezed and triggers star formation, which illuminates the arms, creating the visible spiral structure.

NGC 488 is a good target for small telescopes, even from suburban locations; I've seen it in telescopes as small as a 4-inch refractor with direct vision under the light of a first-quarter Moon. To find it, use the chart on page 26 to locate 3.5-magnitude Alpha (a) Piscium, which is 10^{^} due west of 4th-magnitude Gamma (g) Ceti. Now use your unaided eyes or binoculars to find Mu (m) Piscium about 8^{^} further to the northwest in the Fishes' cord. Center Mu Piscium in your telescope at low power, then switch to the chart on page 29. From Mu Piscium, move 1^{^} southsouthwest to 7th-magnitude 95 Piscium. Now move about 50⁰ west to a wide pair of 8.5-magnitude stars (a) oriented eastnortheast to west-southwest and separated by about 20⁰ . Next move about 35⁰ westsouthwest to 7.5-magnitude Star b. NGC 488 is only about 10⁰ west of Star b.

At 33^ in the 5-inch, NGC 488 can be seen as a small but bright and highly condensed glow just northeast of a roughly 12th-magnitude star. At a glance the light

from the galaxy and star seem to meld, making the galaxy appear larger than it is. Once you realize that a star is contributing to the overall view, the galaxy suddenly shrinks in the mind's eye. It's a fabulous illusion. Because, the galaxy is so condensed, it takes magnification well.

For this study, I immediately went to 94^ to start. At this power, the galaxy is quite a subtle beauty, displaying a conspicuous starlike nucleus in a soft nest of light 1⁰ across, surrounded by an even softer halo at least twice that extent, which is best seen with averted vision. The proximity of the ~12th-magnitude star is somewhat of an irritant, but it helps to keep the eye focused on the target. The view at 165^ is equally enticing, though I cannot see any further details. Those using larger telescopes should be able to make out some of the thin spiral patterns.

On October 21 and 23, 1976, a 15th-magnitude Type I supernova was discovered photographically 2⁰⁰ west and 111⁰⁰ south of NGC 488's nucleus. Designated SN 1976G, it was discovered about 30 to 40 days after maximum light. Keep watch on this galaxy for future eruptions.

Next to the big dipper, the w of Cassiopeia is arguably the most sought after star pattern in the northern heavens. They're both conspicuous and neither sets as seen from mid-northern latitudes. But unlike the Big Dipper (and its parent constellation Ursa Major), which is rich in galaxies, Cassiopeia lies on the Galactic equator and hosts a wealth of other deepsky spectacles, including include two Messier objects (M52 and M103); six Caldwell objects (NGC 147, NGC 185, NGC 457, NGC 559, NGC 663, and NGC 7635); five Hidden Treasures (NGC 189, NGC 225, NGC 281, NGC 659, and NGC 7789), and four Secret Deep objects (NGC 654, NGC 7790, Stock 2, and vdB 1).

One of the richest deep-sky regions in the celestial W lies only 2½^{^} east-northeast of 3rd-magnitude Delta (d) Cassiopeiae. That's where you'll find five open clusters. They are, in order of brightness, NGC 654 (6.5), NGC 663 (7.1), M103 (7.4), NGC 659 (7.9), and Trumpler 1 (8.1). Note that our target, NGC 654, is the brightest of them all. Yet it's easy to overlook because the cluster “hides” in the glare of a yellowish 7th-magnitude sun, which initially overpowers the view. But, as I will soon describe, this yellow star is actually a member of the cluster.

Nevertheless, NGC 654 can be spied by a keen observer using 7 ^ 35 binoculars under dark skies. Telescopically, it's a tiny and tight grouping of little gems. The cluster's 80 measured members (7th-magnitude and fainter) appear in little clumps scattered across a mere 6⁰ of sky, or 14 light-years. G. Lynga classified it as Trumpler II2r – a rich, detached cluster with little central concentration whose stars have a moderate range in brightness. It's a young cluster, with an age of about 14 million years, or about the same age as the Double Cluster in Perseus.

Astronomers have taken keen interest in NGC 654 because it displays nonuniform extinction across its face, with stars reddened by about 1 magnitude on average. As early as 1975, W. B. Samson (Royal Observatory, Edinburgh, UK) proposed that a dust shell of interstellar matter – swaddling matter left over from the period of cluster star formation – is responsible for the nonuniform extinction across the cluster region. But Sidney W. McCuskey (Warner and Swasey Observatory, Cleveland, Ohio) and his colleagues countered that local dust clouds lying in the cluster direction can explain the observed extinction, which is very patchy. Besides, the researchers failed to find evidence that the extinction varies with distance from the cluster center as might be expected with a dust-shell model.

Some of the cluster's stars also display a large color excess – the difference between the observed color of a star compared to its spectral type. Color excess indicates the amount of interstellar reddening suffered by the light from the star when it passes through dust in space. In some clusters, this extinction is caused by the presence of hot and ionized dust circumstellar envelopes around stars.

But this does not appear to be so in the case of NGC 654. In a 2008 Monthly Notices of the Royal Astronomical Society (vol. 388, p. 105) Indian astronomer Biman J. Medhi (Aryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital) and colleagues published their polarimetric observations for 61 stars in the NGC 654 region. The data show evidence for the presence of at least two layers of dust along the line of sight to the cluster, which lies at a distance of about 7,800 light-years. They estimate the distances to the two dust layers to be about 652 and 3,300 light-years, placing the clouds much closer to the Sun than the cluster. The dust forms a ring with the central hole coinciding with the center of the cluster. The foreground dust grains, then, appear to be responsible for the nonuniform extinction towards the cluster, whose least reddened stars lie close to the cluster center.

Photoelectric observations and proper motion studies of NGC 654 have helped astronomers determine which stars belong to the cluster. These studies have identified the 7th-magnitude yellow supergiant star HD 10494 as a likely member with a recessional velocity of about 31 km/sec.

To find this hidden treasure you can star and cluster hop. Start by using the chart on page 30 to locate Delta Cassiopeiae, then 5th-magnitude Chi (w) Cassiopeiae nearly 1½^{^} to the southeast. The 6th-magnitude star 44 Cassiopeiae forms the northeast apex of a near-equilateral triangle with Delta and Chi. Center that star in your telescope then see the chart on page 33. Open cluster NGC 659 is only about 10⁰ north-northeast of Chi, and open cluster NGC 663 is only 35⁰ northeast of it. Our target is only 40⁰ north-northwest of NGC 663. It sits just north and slightly west of a 7th-magnitude sun (Star a) that shines with a rich golden hue; this is the yellow supergiant HD 10494. Note that the magnitude 9.5 star a few arcminutes to the west is not a cluster member, but it adds to the cluster's apparent beauty.

Using direct vision through the 5-inch at 33^ the cluster appears as a breath of circular light hugging a bright topaz-yellow sun. This nebulous knot transforms into a beautiful fuzzy butterfly with averted vision; thus my nickname for the cluster. The butterfly's upward-flapping wings open toward the 7th-magnitude star like a reverse letter “C”. With averted vision and 33^, the cluster resolves into little patches of stardust with an obvious congregation at the northwest end, making it appear quite irregular.

At 60^, the cluster's vast majority of 11th- and 12th-magnitude suns form a 6⁰ -long ellipse of irregularly bright stars, oriented east–west and flanked to the south by milky starlight. At 94^, the greatest congregation of some two-dozen

suns looks like two superimposed clusters: one shaped like a tadpole (oriented roughly east–west) and an inverted V of stars (oriented north–south).

The cluster is small enough, and bright enough, to handle high magnifications. In the 5-inch, the most comfortable power is 180^, which shows the shapes just described burning against a fainter scrim of dim suns. If you look closely at the 7th-magnitude sun, you will see an obvious 11th-magnitude sun about 1.5⁰ north of it, and another 11th-magnitude sun about 1⁰ north-northeast of it. That latter star is another nonmember.

By the way, if you can get a 2^{^} field of view at low power, all three clusters – NGC 654, NGC 663, and NGC 659 – will fit comfortably in the field with 44 Cassiopeiae. In physical space, NGC 654 (~7,800 light-years distant) lies between the other two: NGC 663 ( The Horseshoe Cluster) is a bit closer at ~7,200 light-years; NGC 659 is a tad farther away at ~8,200 light-years.

Secret Deep 5 (Collinder 463)

S

M ost backyard astronomers are aware of Collinder 399, the pretty Coathanger asterism in Vulpecula (Hidden Treasure 97). In my Deep-Sky Companions: Hidden Treasures, I also spotlight two other Collin-der clusters: Collinder 69 (the Lambda Orionis Cluster (Hidden Treasure 29)) and Collinder 72 (the Lost Jewel of Orion (Hidden Treasure 31)). Now I take you to the forgotten high northern reaches of Cassiopeia, to Collinder 463, a large and beautiful cluster “reflected” in the vain Queen's mirror – a 2^{^} -wide trapezoid of 4th- and 5th-magnitude suns (50, 48, 40, and 42 Cassiopeiae).

This mirror is of my own invention. I think it's easier to see the Queen of Ethiopia sitting in her chair or throne, if you envision the chair as depicted on page 36: with Epsilon (ε) and Delta (d) as the raised back, Gamma (g) and Kappa (k) as the seat, and Alpha (a) and Beta (b) as two legs. I first saw the throne depicted this way in Lou Williams' 1950 book A Dipper of Stars (Follett Publishing Company, Chicago). As a child, I found it easier to imagine the Queen seated in this celestial throne than the way she's positioned in classical star charts. If you adopt my nonclassical version of the Queen, look for her in profile: Iota (i) Cassiopeiae is the Queen's head; the mirror is being held in her bent arm with Phi (c) Cassiopeiae at the elbow.

You'll find the Queen's mirror roughly two-thirds of the way along an imaginary line between 3rd-magnitude Epsilon (ε) Cassiopeia, the easternmost star in the Celestial W, and the North Star (see the chart on page 34). The mirror marks a little spur in the eastern reaches of the Milky

Way that sweeps past 3.5-magnitude Gamma (g) Cephei, just a little more than 10^{^} from the North Celestial Pole. Collin-der 463 lies in the middle of the mirror, midway between 40 and 48 Cassiopeiae. It is, in fact, the largest star cluster in the constellation.

The Swedish astronomy graduate student Per Arne Collinder (1890–1975) discovered the cluster, which he listed in his 1931 doctoral dissertation “On structural properties of open galactic clusters and their spatial distribution.” Collinder was a surveyor by profession, spending much of his career on the seas around Sweden and in the Arctic. He devoted his life to the history of astronomy in his retirement, when he became historian of the development of astronomy in his homeland. His records are kept at the Uppsala Astronomical Observatory in Sweden.¹

Collinder 463 is a large and loose Galactic cluster close to the Sun near the edge of the Orion arm – the same one that carries our Sun. At the cluster's given distance, it spans 38 light-years of space.^{3 4} It's also relatively young, being only 150 million years old. That makes Collinder 463 the same age as M35 in Gemini. But Col-linder 463 is nearly two times larger than M35 in true physical extent. Since Collin-der 463 is only about 220 light-years closer, we see it almost twice as large as M35 in the night sky.

In apparent size and magnitude, Collinder 463 is more akin to NGC 752, a magnitude 5.7 open cluster in Andromeda that spans a whopping 75 ⁰ of sky. NGC 752, however, lies nearly twice as close. With an age of 2 billion years, NGC 752 is also one of the oldest open clusters known. Still, isn't it interesting that Collinder 463, which is visible to the unaided eye under a dark sky (just like NGC 752), went unnoticed by so many great observers. NGC 752, on the other hand, which is just as bright and about 25 percent larger than Collinder 463, was at least nabbed by the keen gaze of Caroline Herschel in 1783. Perhaps Col-linder 463's position so close to the north celestial pole caused it to be ignored for so long. Collinder 463 stands just far enough away from the central madness of the Cassiopeia Milky Way to be easily overlooked.

To see Collinder 463 with the unaided eye, you'll need to be under a dark and transparent sky. I find that if I orient my head so that Collinder 463 appears to the upper left of 50 Cassiopeiae, then stare at 50 Cas with direct vision, NGC 463 pops into view with averted vision. It's an intriguing sight in 10 ^ 50 binoculars, appearing as wide splash of about a dozen suns 8.5-magnitude and fainter.

The cluster is an eye-grabber in richfield telescopes, which are best for showing such a large celestial treasure. In the 5-inch at 33^, my eye was immediately attracted to a pretty neck of stars in the southeast quadrant of the cluster that connects to a roughly 10⁰ -wide trapezoid of relatively bright stars at the cluster's core. In fact, when the cluster's central 30⁰ of stars are seen with south up, they remind me of a plesiosaurus – the large marine dinosaur that swam in the Jurassic seas; or, better yet, how about “Nessie,” Scotland's legendary Loch Ness Monster? An acute triangle of suns in the north forms the dinosaur's head; lines of stars extending to the north-northwest, southwest, and northeast look like the beast's flippers. And a “wagging” tail reaches to the east, before making a sharp jog southward.

Of course, a loose cluster of this size is a virtual celestial Rorschach test; just turn your head and all manner of forms can be created. Although the cluster has only 40 confirmed members (three of them confirmed giants), the field is surprisingly rich. I counted at least 80 stars in a roughly 1 ^{^} sphere without straining, and there's probably a hundred. And while the cluster loses its luster at higher powers and smaller fields of view, I found lots of interesting stellar pairings and other attractive gatherings of stars at 60^. So go out and enjoy this “monster” of a cluster. The good news is that it's circumpolar from mid-northern latitudes. Even when lowest, it stands about 20^{^} above the horizon, so it's always accessible.

S tock 2 is a surprisingly bright and large open cluster about 2^{^} northnorthwest of the great Double Cluster in Perseus. Like the latter wonder, it lies near the Galactic equator in the stellar tapestry of the winter Milky Way. And while Stock 2 is just as bright as the Double Cluster, it lacks a strong central condensation (the Double Cluster has two!), which makes it less obvious; imagine seeing two concentrated flashlight beams against a distant background versus that of a single diffuse beam. Indeed, the irregularly bright suns of Stock 2 are coarsely scattered across two Moon diameters of sky in a rich band of Milky Way, causing it to almost blend with the background. Yet, once detected, Stock 2 springs to life, becoming quite obvious, especially in binoculars and wide-field telescopes.

What's visually intriguing is that while the Double Cluster lies some 7,300 light-years distant in the Perseus Arm of the Sun), Stock 2 is a foreground object 1,100 light-years distant (lying almost in front of the Double Cluster) in the Orion spiral arm – the same spiral arm in which our Sun and the stars of Orion reside.

If the Double Cluster were at the distance of Stock 2, each member would span three Moon diameters and shine more than 100 times brighter than it does now in the sky. Conversely, if Stock 2 were at the distance of the Double Cluster, it would appear as a roughly 10th-magnitude cluster about 8⁰ in apparent diameter. As it stands, despite Stock 2's closeness to us, we see it strongly obscured by dense and patchy interstellar dust clouds along this line of sight.

Ju¨rgen Stock at Warner and Swasey Observatory found Stock 2 while searching blue objective prism plates along the Galactic equator. He found the new cluster based on the spectral class and approximate magnitudes of its stars. He catalogued it as a cluster in 1956.

Interestingly, Stock 2 is a Trumpler class I2m, meaning it's a detached and moderately rich cluster with a strong central concentration and a medium range in the brightness of the stars (though the visual appearance through a small telescope is of a loose aggregation of suns hardly concentrated at all!). In their wonderful book Star Clusters, Archinal and Hynes list Stock 2 as having 166 members 8th-magnitude and fainter. But recent studies have increased that number dramatically. In a 2000 Astronomy & Astrophysics (vol. 143. p. 409), D. C. Foster and his colleagues used the cluster's proper motion to separate members from background and foreground stars. The team found 634 stars with a membership probability equal to, or greater than, about 50 percent to a limiting blue magnitude of about 20, corresponding to late-M dwarfs at the distance of Stock 2.

Stock 2 has long been classified as a young cluster, with an age ranging anywhere from 100 million to 170 million years. But these values are not consistent with results obtained by Salvatore Sciortino (Astronomical Observatory of Palermo, Italy) and colleagues, who used the ROSAT satellite data to assess the X-ray luminosity level of 112 high-probability cluster members. As reported in a 2000 Astronomy & Astrophysics (vol. 357, pp. 460–470), their measurements of the cluster's X-ray emission revealed that it more closely resembles that of a much older cluster, having an age intermediate between the Hyades (~700 million years) and the Pleiades (~100 million years).

Determining the lithium abundance of Stock 2's members may help to refine the cluster's age. Lithium (the third element in the periodic table) formed together with hydrogen and helium in the immediate aftermath of the Big Bang. All stars contain lithium. But those massive enough to start burning hydrogen into helium also destroy lithium in the process – in part through slow mixing as the star rotates; in part through diffusion, whereby a star's constantly churning surface pulls lithium from the surface and drags it into the star's hydrogen-burning core where it is destroyed.

Our Sun, a middle-aged star, has only about 1 percent of its original lithium. In contrast, brown dwarfs – the dimmest and least massive kind of star – never get hot enough to burn hydrogen, so they retain most of their lithium. The highest-mass brown dwarfs, however, will eventually burn the element. Thus, determining the highest mass of brown dwarfs still containing lithium in the cluster can give astronomers an idea of its age. Sciortino et al. believe that future high-resolution lithium observations will settle the age debate that their X-ray survey has opened.

To find Stock 2, use the chart on page 38 to find the Double Cluster, which is about 7½^{^} east-southeast of 2.7-magnitude Delta (d) Cassiopeiae (Ruchbah). The Double Cluster appears to the unaided eye as a 4th-magnitude fuzzy knot in the gentle folds of the Milky Way. It is a beautiful and unmistakable peppering of suns forming two mounds of highly condensed starlight spread across 25⁰ of sky.

Visible just north of the cluster's westernmost member (NGC 869), you'll find a 1½^{^} long ellipse of about a half-dozen 6th-magnitude suns; the two most obvious of which are 7 and 8 Persei, just north of NGC 869. The center of Stock 2 is 1^{^} due north of the northernmost star (a) in the ellipse.

In binoculars, Stock 2 appears as 1^{^} -wide scintillating flurry of irregularly bright suns. It's simply a low-power object. For me, 33^ in the 5-inch is the ideal power to appreciate this diffusion of stellar gems. I spotted some 80 irregularly bright members arranged in a multitude of patches across 1^{^} of sky. The cluster's western side is arranged in two overlapping loops, each 20⁰ wide, and oriented north– south. A zipper of stars juts to the east, where it ends in “two little feet.” That's why I call the cluster “9” – because the overall shape of its brightest stars reminds me of the lead character in Tim Burton and Timur Bekmambetov's animated fantasy of the same name. Known as “Stichpunks” to fans of the film, 9 is a courageous little mechanical humanoid (part soul of his creator) with huge binocular-like eyes and a burlap body dominated by a zipper that runs up his torso.

I don't recognize a cluster core, though two tiny Y-shaped strings of stars, each just a few arcminutes long with some nice stellar pairings can be found here. The cluster's most prominent pair (8th-and 10th-magnitude suns separated by ~2⁰ ) lies on its southwest edge and is oriented southeast–northwest. The brighter of the two has an interesting ruddy hue. Use powers between 60^ and 100^ to investigate the cluster's multitude of fainter pairs and interesting groupings, which include stars arranged in letters, such as “P,” “Y,” “L,” “O”, “J,” etc. Relax your mind and have fun with the view.

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Darth Vader's Starfighter

NGC 936

Type: Barred Spiral Galaxy (SB0 (rs))

Con: Cetus

RA: 02^h 27.6^m

Dec: -01^{^} 09⁰

Mag: 10.2

SB: 13.5 (Rating: 4)

Dim: 5.7⁰ ^ 4.6⁰

Dist: ~54 million l.y.

Disc: William Herschel, 1785

w. herschel: [Observed January 6, 1785] Considerably bright, a very bright nebula with a chevelure of 3 or 4⁰ diameter. (H IV-23)

ngc: Very bright, very large, round, much brighter in the middle to a nucleus, preceding of 2.

ngc 936 is a small but beautiful barred-spiral galaxy in the middle of Cetus the Whale's neck, almost midway between mid-4th magnitude Delta (d) Ceti⁵ and the celebrated “winking” variable star Mira. It's also about 1¼^{^} west, and a tad south, of 5.5-magnitude 75 Ceti. In a way the galaxy's position places it just beyond notice, given that most attention in the area is either given to Mira or the bright Seyfert galaxy M77, which lies only about 1^{^} southeast of Delta. Interestingly, NGC 936's core is extremely condensed and bright, so it's a great object for suburban observers.

Note that Herschel classified it as a planetary nebula (his Class IV object) owing to its round shape. This classification may have caused the great nineteenth-century observer Admiral William Henry Smyth (1788–1865) to see it not only as round, like a planetary, but also “bluish white, and pale, but very distinct, and brightening toward the centre.” The color he saw was probably the result of mental suggestion, given that many bright planetary nebulae shine with a green or aqua hue.

But as modern images clearly show, NGC 936 is a prototypical barred spiral galaxy, seen inclined 40^{^} from face-on. It belongs to the Cetus–Aries Cloud of galaxies and is receding from us at 1,430 km/ sec. The galaxy is quite large. If we accept a mean distance estimate of 54 million light-years, the galaxy measures more than 90,000 light-years in linear extent.

Our target actually is joined by (though not interacting with) the much fainter barred spiral galaxy NGC 941 (magnitude 12.4) 12.6⁰ to the east, the edge-on spiral NGC 955 (magnitude 12.0) 44⁰ to the east, and several other dimmer anonymous companions. In true linear projection, NGC 941 lies nearly 400,000 light-years from NGC 936, while NGC 955 is about 1.3 million light-years distant from it. This loose group is about half the size of the Local Group; so large telescope users should have fun trying to imagine this as they peer into this region of space.

Deep images of NGC 936 reveal it to be of the earliest barred spiral class, showing a nearly smooth, extended disk with an abnormally prominent bar that ends well inside the edge of the disk (out to a distance of 20,000 light-years), which has a luminosity of nearly 6 billion Suns. A diffuse, massive, ill-defined but definite spiral pattern exists outside the end points of the bar, where we see a parallel pair of arcuate arms with fainter extensions that form a complete ring around the nuclear region, which consists of a very bright and diffuse nucleus or inner lens (0.6⁰ ^ 0.4⁰ ). This oblate bulge also has a luminosity of nearly 6 billion Suns.

The spiral features that thread through the disk of NGC 936 are generally diffuse and ill-defined. The arms, though massive, are smooth, and indefinite – similar to the pattern seen in the early mixed spiral galaxy NGC 2655 (Hidden Treasure 48) in Camelopardalis.

A 2010 European Southern Observatory (ESO) press release noted that the appearance of the galaxy (as imaged by the 8.2-meter telescopes of ESO's Very Large Telescope on top of Cerro Paranal, Chile; see below) bears a striking resemblance to “the Twin Ion Engine (TIE) starfighters used by the evil Dark Lord Darth Vader and his crew in the epic motion picture Star Wars. The galaxy's shiny bulge and a bar-like structure crossing it bring to mind the central engine and cockpit of the spacecraft; while a ring of stars surrounding the galactic core completes the parallel, corresponding to the wings of the TIE fighters that are equipped with solar panels.” As with other early-stage barred spirals, NGC 936 comprises exclusively old stars and shows no sign of any recent

star formation. And, as with most other galaxies, no one knows if it is dominated by a large amount of dark matter.

To find this unusual treasure, use the chart on page 42 to locate 75 Ceti, which is about 2¼^{^} southwest of Delta (d) Ceti. Center that star in your telescope at low power, then switch to the chart on this page. From 75 Ceti, move a little less than 30⁰ northwest to 9th-magnitude Star a. Now move about 45⁰ west-northwest to 7th-magnitude Star b, which has a 9th-magnitude companion about 6⁰ to the south-southeast. NGC 936 is about 25⁰ south of that star pair.

At 33^ in the 5-inch, NGC 936 is a bright, small (3⁰ ), and highly condensed, round glow of mostly uniform brightness but with a definite central concentration; the view begs for more power. At 60^, the galaxy's nucleus burns with a fiery intensity, like a hypnotizing eye. It truly does look like a bright planetary nebula with a punchy central star. The intense nucleus lies in a soft nest of circular light, which itself is surrounded by an equally soft and circular collar of dim emission.

Every now and then I saw with averted vision NGC 941 popping in and out of view, as if vying for attention (it appears as a large dim glow just above the sky

background). NGC 936's outer halo definitely needs averted vision; it vanishes with a direct gaze; even then, like NGC 941, it is flirtatious, flitting in and out of view appearing slightly out of round, oriented slightly northwest–southeast.

NGC 936's nuclear region takes magnification well, so crank it up! I studied the inner lens at 330^ with little problem. At that magnification I could see its prominent bar with weak concentrations on either end of it. I could not justify seeing bright arcs, just a ring of light around that lens, though I'm certain larger telescopes can eek out such minute detail.

As reported on International Astronomical Union Circular number 8171, on July 29, 2003 UT, the great Australian supernova discoverer Robert Evans of Hazelbrook, New South Wales, discovered a magnitude 13.8 supernova in NGC 936 through his 12-inch reflector. He found it about 20⁰⁰ southeast of the nucleus, noting that he detected nothing to magnitude 15 on July 3 UT. Designated Supernova 2003gs, the new object had a peculiar spectrum roughly consistent with a Type Ia supernova perhaps one week after maximum light.

In one popular model, a Type Ia supernova results from the violent explosion of a white dwarf star that may be in a close binary system with a red giant star from which it accretes matter. The white dwarf feeds on its companion's outer layers until it essentially overdoses and erupts as a supernova. This occurs when the mass of the white dwarf reaches 1.4 solar masses (40 percent more mass than that of our Sun); a runaway nuclear chain reaction occurs, causing the white dwarf to destroy itself by exploding. For white dwarfs in such systems, gluttony can be sinfully bad news!

D o not be fooled by ngc 1084's magnitude. It is a small but obvious galaxy about 3^{^} northwest of 4th-magnitude Eta (Z) Eridani (Azha), just east of the Cetus border, or about 2½^{^} east-northeast of the close pair of 6th-magnitude suns 77 and 80 Ceti. It's very visible in a small telescope, being highly condensed, making it an excellent target for suburban observers. Its declination places it just a little lower than that of the southernmost portion of Orion's Sword.

NGC 1084 is actually the brightest and easternmost of a half-dozen galaxies near 80 and 77 Ceti with the others being as follows: NGC 991 (magnitude 11.7) about 30⁰ to the north; NGC 1022 (11.3) about 1¼^{^} to the northeast; and NGC 1035 (12.2), NGC 1052 (10.5; see page 50), and NGC 1042 (11.0) making a pretty 30⁰ -wide triangle about 1^{^} to the southeast. All belong to the Cetus–Aries Cloud of galaxies and lie about 60 million light-years distant.

Despite its somewhat ungainly appearance in some images (which tend to burn out the core), NGC 1084 is, at a glance, a typical, late-type spiral galaxy, receding from us at about 1,500 km/sec. Like other Sc galaxies, NGC 1084 has a small central nucleus compared to its main massive spiral arms, two of which form a regular grand-design S-shaped spiral pattern with much irregular structure, bright knots and emission objects. But while NGC 1084's northwestern arm is well defined (being lined on its inside edge with a dust lane), the spiral pattern on the eastern side of the galaxy (the one nearest to us) is not so easy to trace; here, two arms start as thin, luminous threads that overlap after unwinding by half a turn – beyond that the spiral pattern is confused, being a mishmash of dust lanes and feathery spiral segments.

The galaxy's disk is moderately sized, spanning some 56,000 light-years in its longest extent, and mildly inclined at 63^{^} from face-on. It has a total mass of some 50 billion Suns. The galaxy's weak nuclear bulge is elongated along the disk's major axis and shows no sign of a bar. In a 2000 Astronomy & Astrophysics (vol. 363, pp. 843–850), Russian astronomer Alexei V. Moiseev (Special Astrophysical Observatory) found giant star-formation regions in a 11,500 light-years-long “spur” in the northeast part of the galaxy that “avoids the bright HII regions.”

The most intriguing feature, he says, was not the spur itself, but the strong unusual gas motions around it (up to ^150 km/sec!). To explain this curiosity, he suggests either (1) an infall of high-latitude gas clouds (intergalactic clouds or clouds expelled from the disk earlier) onto the galactic disk, which could trigger star formation, or (2) an interaction with a gas-rich dwarf galaxy accompanied by tidal disruptive merging.

As for the latter theory, Moiseev notes that a small “island” of H-alpha emission does exist there, which may be associated with a radio tail that begins there and extends to another radio source 3.5⁰ from the galaxy. “As no HI map at 21 cm is available for NGC 1084,” Moiseev says, “one cannot confirm whether this radio tail contains some expelled gas. But the configuration resembles a tidal tail as usually developing on the opposite side of a galaxy colliding with another one. Therefore, the gas flow twisted in the northern half of NGC 1084 might be accretion.”

In a 2007 Monthly Notices of the Royal Astronomical Society (vol. 381, pp. 511–524), S. Ramya (Indian Institute of Astrophysics, Bangalore) and colleagues discuss their study of star formation in NGC 1084, which supports Moiseev's second theory. They found star-formation rates for a few of the complexes to be as high as 0.5 million solar masses per year, with the complexes themselves lying in the age range 3 to 6.5 million years. “The star formation in NGC 1084 has taken place in a series of short bursts over the last 40 million years or so,” they say. “It is proposed that the likely trigger for enhanced star formation is merger with a gas-rich dwarf galaxy.”

Indeed, Moiseev says that in a 2010 University of Strasburg preprint (http:// cdsads.u-strasbg.fr/abs/2010arXiv1003. 4860M) Martinez-Delgado and colleagues say they have obtained ultra-deep images of this galaxy. “They detected several external plumes or tidal tails around NGC 1084,” Moiseev says. “Now the fact of merging with one (or several) dwarf companions is directly confirmed.”

To find this possible extragalactic cannibal, use the chart on page 47, to first locate 2nd-magnitude Alpha (a) Ceti (Menkar). Now look for Eta (Z) Eridani a little more than 10^{^} (a fist held at arm's length) to the south and ever so slightly west.

Now use your unaided eyes or binoculars to find 80 Ceti, which is 5^{^} to the westnorthwest. You'll know when you have this star because similarly bright 77 Ceti lies only about 20⁰ to its west. Center 80 Ceti in your telescope at low power and switch to the chart on page 50. From 80 Ceti, move 40⁰ northeast to a pair of 8.5-magnitude stars (a), which are oriented northeast to

southwest and separated by about 5⁰ .Now make a careful sweep about 45⁰ southeast to 8.5-magnitude Star c, which has an 11th-magnitude companion about 4⁰ to the east-southeast. Finally, move about magnification to 94^ brings out some feathery details to the egg's rim. The galaxy started to reveal itself at 164^, when I saw two arcs: a long one at the position of the bright northwestern arm (it starts at the northeast side of the galaxy (the spur?) and winds around to the west, where it gradually fades); and a short and stubby arm beginning at the southwestern end of the egg. Averted vision at this power also shows the core to be slightly brighter and elongated.

CCD imagers take note: NGC 1084 is a great galaxy to watch for supernovae, with four known to date having occurred over the last half century. They are: SN 1963P, SN 1996an, SN 1998dl, and SN 2009H. Happy hunting!

ngc 1245 is a relatively small, dim, but rich open cluster a little more than 3^{^} southwest of 2nd-magnitude Alpha (a) Persei, roughly midway between Alpha and 4th-magnitude Kappa (k) Persei. It's another one of those small and compressed wonders that's greatly overshadowed by larger, brighter, and more visually accessible clusters, such as the Alpha Persei Moving Cluster (Hidden Treasure 14) and M34, about 7^{^} to the southwest. But despite NGC 1245's seemingly diminutive nature, it is a surprisingly rich cluster and quite the spectacle under a dark sky.

In 1930, Trumpler classified NGC 1245 as a rich, detached cluster with little concentration. As open clusters orbit the Galaxy and age, they gradually “evaporate,” losing their less massive stars first. NGC 1245 is, in fact, one of the senior members of the open cluster family, being about 1 billion years old. It's an irregular and loose aggregation spread across 27 light-years of space in the antigalactic direction. It lies close to the Perseus arm, nearly 1,500 light-years below the plane of the Galaxy. While most of the cluster's brighter stars are slightly blue main-sequence (hydrogen burning) stars, the cluster also contains a large population of evolved orange (hydrogen-shell burning) stars, indicating that it might belong to the Galaxy's old disk population.

In a 2003 Bulletin of the Astronomical Society of India, Annapurni Subramaniam (Indian Institute of Astrophysics) confirmed the cluster's age and the fact that it appears to have a small deficiency of bright stars near the center of the cluster, which matches the visual impression through backyard telescopes; the brightest stars form several looping hollows that take on a starfish pattern.

As I mentioned earlier, all star clusters experience the tidal force of the Galaxy, which can result in the cluster losing low-mass stars to the Galactic field. And this appears to be the case with NGC 1245 as we see it today. NGC 1245 is highly relaxed, and its stellar population is strongly segregated by mass. Its outer periphery is indeed enriched with low-mass members while devoid of high-mass members out to its tidal radius of 54 light-years. “The lost stars could be present in the corona of the cluster,” Subramaniam says, noting that as recently as 2002 it has been discovered that clusters in general have large coronae, which contain a large fraction of cluster stars.

In a 2004 Astronomical Journal (vol. 127, pp. 2382–2397) Christopher J. Burke (Ohio State University) and his colleagues derived a total cluster mass of about 1,300 Suns, a distance of 9,100 light-years, and found it to have a slightly subsolar metal-licity. Burke et al. have also conducted searches for transiting extrasolar planets to assess the frequency of close-in extrasolar planets around main-sequence stars in several open clusters. They began by surveying stars in NGC 1245 and expected to see two transits. Their preliminary search of the data, published in 2003, revealed a transit candidate with a depth of 4 percent. They observed the transit on two separate nights. “Unfortunately,” the researchers lament, “the transit is unlikely to be a planetary transit, since the [light curve] is indicative of a grazing binary eclipse. [Those of ] planetary transits tend to be boxier in shape with more rapid ingress and egress durations and flatbottom eclipses.”

Burke and Joshua Pepper (Ohio State University) also determined the variablestar content of the cluster. Out of 6,787 stars observed to a visual magnitude of 22, they found 14 stars with clear intrinsic variability that are also potential cluster members and 29 clear variables that are not cluster members. None of these variables had been previously identified. Four stars at the main-sequence turnoff of the cluster have light curves consistent with Gamma (g) Doradus variability. If these Gamma Dora-dus candidates are confirmed, they represent the oldest and coolest members of this class of variable discovered to date.

To find this fascinating cluster use the chart on page 51 to locate Alpha Persei. Now look about 2½^{^} west for 4th-magnitude Iota (i) Persei. Center Iota Persei in your telescope at low power, then switch to the chart on page 54. From Iota, make a slow sweep 50⁰ southeast to 8th-magnitude Star a. Now make another sweep 50⁰ south to 6th-magnitude Star b, then slide about 30⁰ south-southwest to 6.5-magnitude Star c. NGC 1245 is about 35⁰ southeast of Star c.

In the 5-inch at 33^ under a dark sky, NGC 1245 is quite impressive, being a tiny packet of bright and faint suns in a starfish pattern. This brighter form is sprinkled over with dim suns that look like droplets of dew on a flower. The cluster's core is exceptionally granular at low power. At 60^, some 40 to 50 prominent cluster members are loosely scattered across

Perseus

W

10⁰ of sky, forming a series of seemingly overlapping ovals, especially in the east– west direction near the “core.” The core at first has a snaking river of about eight similarly bright stars at its northern border running west to northeast. The granular texture is between the two brightest stars to the south and east of this river.

In photographs, the cluster looks likea lily to me, but I cannot fully appreciate this impression in the 5-inch. There really are no spectacular double stars, though a careful survey will show the occasional odd pairing of a bright sun with a dimmer companion. No, the simple beauty of this cluster lies in its elegant richness at low power. I just cannot escape seeing the starfish form of bright suns, sprinkled over with

celestial “sea salt” (a granular texture composed of countless dim suns). For this reason Icall NGC 1245 the “Patrick Starfish” cluster. It's a special imaginary creation for young Alison Nagler, daughter of Tele Vue Optics' president David Nagler, who's a fan of the animated kids' TV show “SpongeBob Squarepants”; Patrick, a pink starfish, is SpongeBob's best friend and neighbor.

At higher powers, you may find the main concentration of the cluster's most prominent suns mixing with other stellar gatherings to create more fanciful shapes. I've found letters – such as A, Y, L, G, and U– floating in the darkness like letters in an alphabet soup. (I must admit that I made this observation before I had learned from Larry Mitchell of Houston, Texas, that William Herschel observed a similar pattern, writing, “the bright stars arranged in lines like interwoven letters.”)

Perhaps with the age of this cluster in mind, I can see it as a cluster in the process of “falling apart,” especially where the arms appear “separated” from the central framework, as if the cluster's being dismantled. Have fun with your own imaginings.

W e've now come to one of the most perfect examples of a grand-design barred spiral galaxy in the heavens: NGC 1300, a cosmological wonder of elegance, grace, and style. This southern galaxy is much sought after from northern locals, though it may prove difficult from some suburban locations with poor horizons. It's best to pursue it under a dark sky with few or no obstructions.

The galaxy is only 0.3 magnitude fainter than M98 and M91 in Coma Berenices, and it has about the same surface brightness as them as well. The difficulty is not so much its declination – which places it a little bit higher in the sky than M 41 in Canis Major – but its relative isolation in the weak star fields of Eridanus. But many northern observers have spied it in 4-inch and smaller telescopes. For instance, the late, great deep-sky observer Walter Scott Houston (1912–1993) of Connecticut observed it in a 3½-inch Questar.

If you see this wonder, you're looking at a giant extragalactic system more than 150,000 light-years across and some 70 million light-years distant in the Fornax Cluster and Eridanus Cloud of galaxies. The light we see emanating from it today first escaped that galaxy during Earth's Cenozoic period around the time of the extinction of the dinosaurs. We see the galaxy's disk inclined 43^{^} from face-on, and it has a total mass of 150 billion suns. In deep images, like the one on page 57 taken by the Hubble Space telescope, NGC 1084 is a fantastic tapestry of starlight and glowing gas mixed with slithering wisps of dark obscuring interstellar dust.

Most alluring is the way the galaxy's brilliant spiral arms fly off of the ends of the galaxy's bar and bulge, looking like water jetting from a reciprocating lawn sprinkler. Most galaxies of this spiral-arm subclass (s) have dominant, massive arms rather than a weak, filamentary pattern where the arms fray like feathers from an almost-complete ring. There is a concentration of HII regions where the arms join the bar, and mainly so on the western side. The western arm also contains several very luminous HII regions, while the eastern arm shows some less luminous enhancements.

In the HST image, note how the bar blends with the smooth, and equally majestic, elliptical bulge, which measures some 150,000 light-years across. Two straight dust lanes line the opposite sides of the nucleus and can be traced to the ends of the bar, where they turn sharply and follow the insides of the spiral arms. The tightly wound arms extend roughly 180 degrees before fading. The far ends of the arms straighten out, rather than curving back into a pseudo-ring.

At HST's resolution, a myriad of fine details, some of which have never before been observed, is seen throughout the galaxy's arms, disk, bulge, and the very small and extremely bright nucleus. Supergiant stars, star clusters, and star-forming regions are well resolved across the spiral's thin, knotty arms. Smooth dust lanes trace out fine structures in the disk and bar. Numerous more distant galaxies are visible in the background, and are seen even through the densest regions of NGC 1300.

These features are not unique to NGC 1300. Most barred spirals with “granddesign” structure – meaning a small but distinct nuclear spiral centered on the larger spiral pattern formed by the galaxy's arms (a spiral within a spiral) – share several distinctive features: a large-scale prominent bar; two straight and symmetrical dust lanes, each on the outside of the otherwise smooth bar; and recent and robust star formation in the arms near the ends of the bar, which occurs in a number of discrete clumps.

The core spiral of NGC 1300 spans about 3,300 light-years, and the HST image resolves it into a series of tightly wound armlets, outlined in dust and stellar populations. This core also is a site of considerable star formation. Models suggest that the gas in a bar can be funneled inwards, and then spiral into the center through the grand-design disk, where it can potentially fuel a massive central black hole. But, unlike other spiral galaxies, including our own Milky Way, NGC 1300 doesn't appear to harbor one. NGC 1300 is not known to have an active nucleus, indicating, again, either that there is no black hole, or that it is not accreting matter.

To find this “perfect” barred spiral, use the chart on page 55 to locate 3rd-magnitude Gamma (g)

Eridanus

h3565

NGC 1301

NGC 1297

NGC 134

S

nucleus surrounded itself by a small oval glow with fuzzy edges.

At 60^, I immediately suspected seeing the galaxy's barred spiral structure. The outer arms appeared very tattered. These twin arms on opposite sides of the galaxy mirror one another as they sweep away from the bar.

The galaxy comes to life at powers between 94^ and 165^. But, to see the most detail, you might have to battle between low-power views (which condense the light, making faint structures easier to see) and high-power views (which help to resolve these faint structures, though they are not as immediately visible).

With time and concentration, I could make out a tiny starlike nucleus embedded in the central lens from which juts the bar. One arm shoots off from the west end of the bar to the north. The other arm curves from the east to the south. A dim star is trapped between the northwestern arm and the inner lens. Can you see it?

Like ngc 1245 (secret deep 9), open cluster NGC 1342 is another overlooked deep-sky object in Perseus. It lies in a fist-sized celestial chasm, almost midway between the eastern foot of the Hero (3rd-magnitude Zeta (z) Persei) and the head of the snake-haired gorgon Medusa (the 2nd-magnitude eclipsing binary star Beta (b) Persei (Algol)), or about about 5½^{^} west-southwest of 3.5-magnitude Epsilon (ε) Persei.

Many observers were first introduced to NGC 1342 in December 2007, when Comet 17P/Holmes (see next page) passed near the cluster. It was just the latest in a long string of close encounters the comet had with other interesting objects in Perseus. In fact, amateur astronomers used the comet as a sort of celestial tour guide, alerting the public whenever the comet was to pass near a target of interest in the constellation. And it worked.

Many observers got to see Comet Holmes soon after its magnificent outburst on October 23–24, 2007. The comet erupted like a nova, emerging from telescopic obscurity (16th-magnitude) to naked-eye prominence (3rd-magnitude) in just two days, flaring nearly half a million times in brightness (the largest known outburst of a comet in that period of time). The excitement surrounding the sudden flaring of Comet Holmes was tangible.

By the time Comet 17P/Holmes neared NGC 1342, however, it was a telescopic object. Still, seeing these two objects in the same field of view was dramatic – an opportunity to appreciate the threedimensional aspect of the sky, with the comet being a Solar-System object

millions of miles distant and the cluster being 1,700 light-years distant.

That a comet could draw attention to an obscure deep-sky object is not new. Consider the first object in Charles Messier's catalogue (M1, the Crab Nebula), which the great French astronomer independently discovered in 1758 while observing the Comet of 1758. Likewise, French astronomer Jean-Dominique Maraldi (1709–1788) discovered the globular clusters M2 and M15 in 1746 while following the movements of De Cheseaux's Comet of 1746.

Yet, and I find this surprising, NGC 1342, a magnitude 6.7 open cluster 17⁰ across, went unnoticed until William Herschel detected it on December 28, 1799. Today, you can spy it under dark skies in binoculars. How did something so bright and obvious avoid detection? I don't have the answer.

In 1930, Trumpler classed it as IImr, a moderately rich and detached cluster whose moderately bright members are more-or-less uniformly scattered with little concentration. In a 1994 Journal of Mexican Astronomy and Astrophysics (vol. 28, pp. 7–16), J. H. Pen˜ a (Universidad Nacional Auto´ noma de Me´xico) and colleagues report how their photometric studies of NGC 1342 confirm that the cluster seems to have a relatively large number of young stars. Temperatures determined of the hottest stars along with their luminosities have yielded an age estimate of 400 million years – about as old as the Coma Berenices Star Cluster (about the time when the first winged insects appeared on Earth), and about four times older than M34, which is about as far away northwest of Algol as NGC 1342 is to the southeast in apparent angular distance.

To find this pretty object, locate Epsilon (ε) Persei and Xi (x)Per4^{^} to the south. NGC 1342 marks the western apex of an equilateral triangle with those stars. Just raise your binoculars to that location and look for what appears to be a diffuse, 7th-magnitude “comet” immediately south-southwest of an 8.5-magnitude star. Otherwise, from Xi Per, look 5^{^} west for 6th-magnitude Star a, which in binoculars should be a nice triple. Center Star a in your telescope at low power, then switch to the chart on page 62. From Star a, hop about 10⁰ north to 7.5-magnitude Star b. Next, move about 55⁰ northwest to a wide pair of 8th-magnitude stars (c), oriented west-northwest to eastsoutheast and separated by about 20⁰ .NGC 1342 is 50⁰ due north of the southeastern 8th-magnitude star in Pair c.

Although it is just below naked-eye visibility, the cluster is visible in 10 ^ 50

binoculars. At 33^ in the 5-inch I can immediately see about a dozen stars, including a jagged, 10⁰ -long flat ellipse of some half-dozen suns of mixed magnitudes (oriented east-northeast to westsouthwest). The ellipse glitters with tiny flecks of dim stars that seem to scintillate with averted vision.

When I relax my gaze at 60^, I can envision a sea robin swimming south. Its wing-like fins extend to the east and west from the southern part of the cluster, and its tail reaches to the north where it ends at a pretty double star. In their 1998 Observing Handbook and Catalogue of Deep-Sky Objects (Cambridge University Press), Christian Luginbuhl and Brian Skiff see a stingray swimming to the west in these stars.

With averted vision, the cluster's brightest stars lie against a gauzy backdrop of fainter suns. The cluster contains nearly 100 members 8th magnitude and fainter, though only about 50 or so are prominent in the 5-inch.

ngc 1400 and ngc 1407 are the two brightest, and most central, galaxies in the Eridanus A group of galaxies – the largest clump of island universes in the very patchy Eridanus Cluster of galaxies. Lying about 53 million light-years distant, the Eridanus A subcluster includes roughly 50 galaxies (mostly dwarf ellipticals and dwarf lenticulars) within a 1½^{^} circle of sky centered at 3^h 40^m, -19^{^} . And while Eridanus can easily conjure up visions of deep southern splendors, our two targets, when culminating, are about 2^{^} higher in the sky than open cluster M41 in Canis Major.

The pairing of NGC 1400 and NGC 1407 in the sky presents an astrophysical puzzle. Although these two early-type galaxies lie only 12⁰ in apparent distance apart, they are not interacting. In fact, their recessional velocities differ dramatically. NGC 1407 is receding from us at a velocity of 1,776 km/sec (typical of other galaxies in the group), while NGC 1400 is moving at a relative snail's pace: only 549 km/sec – about one-third the velocity of NGC 1407. Thus, in some early studies of the galaxies, some astronomers suspected that NGC 1400 is a foreground object.

The answer to the puzzle is important. As Andrew Gould (Institute for Advanced Study, Princeton, New Jersey) and his colleagues explain in a 1993 Astrophysical Journal (vol. 403, pp. 37–44), since the Eridanus A group contains only two bright galaxies (NGC 1400 and NGC 1407), its mass depends on whether NGC 1400 is a member. NGC 1400's membership also affects what's known as the group's mass-to-light ratio, which determines how much dark matter the cluster harbors.

Using five different methods to determine galaxy distance – including whether it appears coarse and grainy (indicative of a nearby galaxy) or smooth (indicative of a distant galaxy)⁶ – researchers found that not only is NGC 1400 at the same distance of NGC 1407 (~53 million light-years), but also that these two galaxies supply two-thirds of the cluster's light.

Based on available data, NGC 1400's high velocity is not indicative of a rogue galaxy passing through the subcluster but of the subcluster's enormous mass, namely 90 times that of the Milky Way. But the total light output of the Eridanus A group is only twice that of the Milky Way. Thus, the researchers say, the subcluster is awash in dark matter; indeed, Eridanus A is the darkest galaxy group known. Its mass-to-light (mass–luminosity) ratio could be as high as 2,500, though conservative estimates place it around 600. By comparison, the dark-matter rich Coma Cluster of galaxies has a mass–luminosity ratio of only about 200!

If the mass–luminosity of the Eridanus subcluster holds true, and if dark galaxy groups such as Eridanus A are common, they could account for much of the universe's mass and perhaps halt its expansion; but if the universe's critical mass– luminosity ratio is less than 1,600, it will continue to expand forever.

NGC 1407 is 1.3 magnitudes brighter than NGC 1400. It is also much larger. NGC 1407 measures 87,000 light-years across in true physical extent, while NGC 1400 is about seven times smaller. In physical appearance, both of these early-type galaxies are quite simple. Both have a small, bright, and diffuse nucleus with what appears to be a dust ring. In the case of NGC 1400, that inner ring is seen nearly pole on; the galaxy is also surrounded by an extended outer envelope. It's possible that both NGC 1400 and 1407 formed more than half of their mass in a single shortlived burst of star formation (>100 solar masses/year).

As reported in a 2008 Monthly Notices of the Royal Astronomical Society (vol. 385, pp. 667–674), Max Spolaor (Swinburne University, Hawthorn, Australia) and his colleagues used spectroscopic and other data from the ESO 3.6-meter, Subaru 8-meter, and Hubble Space telescopes to determine that the burst most likely involved supernova-driven galactic winds, supporting a monolithic collapse model for galaxy formation and evolution: As a large gas cloud collapses, it triggers a massive burst of star formation; the newly formed stars orbit the core with eccentric orbits, creating what we see as an elliptical galaxy; disk stars form later.

The researchers also speculate that, since their formation, the galaxies have evolved quiescently, and that we are witnessing the first infall of NGC 1400 in the group. They also confirmed that NGC 1400 and NGC 1407 are not interacting, and that NGC 1407 harbors a 1 billion solar mass supermassive black hole at its core.

To find these fascinating extragalactic simpletons, use the chart on page 63 to

locate 5.5-magnitude 20 Eridani. Start with Brilliant Beta (b) Orionis (Rigel). Nearly 20^{^} (two fists held at arm's length) to the westsouthwest is 3rd-magnitude star Gamma (g) Eridani (Zaurak), the brightest star in the region; it's also the same guide star you use to find the famous planetary nebula NGC 1535 (Hidden Treasure 24), Cleopatra's Eye. But you're going to now use your unaided eyes or binoculars to look 6^{^} to the southwest to find 20 Eridani. Center that star in your telescope at low power, then switch to the chart on this page. From 20 Eridani, move a little less than 30⁰ south-southeast to 8th-magnitude Star a. NGC 1407 is 1^{^} to the southeast.

As seen at all powers through the 5-inch, the galaxy is a fine, yet simple, ellipse of light, oriented north-north-east to southsouthwest, about 1⁰ in extent. Its core is bright and starlike. The surrounding disk is magnificently uniform and swells to nearly 2⁰ with averted vision. Under a dark

sky, I find that whenever I use averted vision to view NGC 1400, fainter NGC 1407 suddenly wafts into view like some luminous vapor rising from the depths of space.

Being so near to NGC 1407, and mysterious, NGC 1400 has the capability of stealing one's attention. When I investigate it at moderate to high powers, I can't help but notice that NGC 1400's core is smaller than NGC 1400's; it's a starlike bead surrounded by a little elliptical lens of light that suddenly turns into a larger and more diffuse halo.

When I use 33^ and relax my gaze, I find the area to have other hidden treasures. Most noticeable is 12th-magnitude NGC 1393 about 20⁰ northwest of NGC 1407. With moderate to high powers, I can also see 12.6-magnitude NGC 1402 about 10⁰ west-northwest of NGC 1407.

ngc 1491 is a visually small, and photographically large, emission nebula just a little more than 1^{^} north-northwest of 4.5-magnitude Lambda (l) Persei, the last star in the curved Segment of Perseus. The Segment is a prominent spine of bright stars between the W of Cassiopeia the Queen and the Pentagram of Auriga the Charioteer. It's a graceful arc of moderately bright suns projected against a dynamic section of Milky Way including the Alpha Persei Moving Cluster (Hidden Treasure 14). The Segment's brightest section measures about 10^{^} in length (a fist held at arm's length) and consists of the stars Eta (Z), Gamma (g), Alpha (a), Sigma (s), Phi (p), and Delta (d) Persei. The Segment then curves to the northeast and includes the stars Mu (m), and Lambda (l) Persei. So the overall shape of the Segment is a J or fishhook.

Many of the stars in the Segment lie at distances ranging from about 530 light-years in the Alpha Persei Association to 900 light-years for Mu Persei. At a distance of 1,200 light-years, NGC 1491 lies a little bit further away in this section of the Perseus arm of the Milky Way – between open cluster M34 (1,400 light-years) and the little reflection nebula NGC 1333 (Hidden Treasure 15; 1,100 light-years).

Again, in wide-field images, NGC 1491 is an evolved HII region (a complex expanse of ionized interstellar hydrogen) that extends at least to 35⁰ in red light, with weak diffuse emission out to at least 1^{^} . If we accept the nebula's distance as 1,200 light-years, this glowing cloud spans an impressive 21 light-years of space, about half the linear extent of the Great Orion Nebula. In the widest images I've seen, the nebula complex has a bright 3⁰ -wide “pad” of intensely glowing nebulosity with at least three dimmer “toes” of gas reaching out to the east. Overall, the nebula complex looks like the fossil footprint of one of those flesh-eating Jurassic terrors, such as T-Rex, Allosaurus, or Velociraptor – thus my moniker for the nebula.

In both radio and optical wavelengths, NGC 1491's structure is very inhomogen-ous. Indeed, the nebula's 11th-magnitude type O5 exciting star (BDþ50^{^} 886) is located about 1⁰ east of the the brightest region – with rippling “curtain folds” oriented roughly north-northeast–southsouthwest. Two parallel folds appear in this region northwest of the exciting star. The western and southern extensions, however, are more sinuous. All these folds have the appearance of an ionization front with steep edges. A dark “elephant trunk” in the western fold (the sideways finger of darkness outlined by bright emission) points very clearly towards the exciting star.

The exciting star also lies at the center of a “half-ring” of nebulosity, which can be seen faintly immediately to the star's west (no emission has been detected along the ring's eastern half ). In a 1976 Astronomy & Astrophysics (vol. 48, pp. 63–73), Lise Deharveng (Marseille Observatory) and colleagues note that while the nebula's most outstanding feature (the wrinkled bright emission described above) is very probably from an ionization front, the half-ring of nebulosity immediately west of the exciting star is not; more likely, the half-ring is a shock front reminiscent of the one in NGC 7635, the Bubble Nebula in Cassiopeia (Caldwell 11). This rim, then, would mark the edge of a rapidly expanding shock wave that's washing onto the nebula's shore like a tidal wave intercepting a coastal plain. In a private 2010 communication, Deharveng notes that this structure probably shows a shock between two flows of material in opposite directions, one of material ejected by the central star (present and not past activity), the other of material receding from the high density ionization front.

In the researchers' model of NGC 1491, the nebula is open (mass limited) to the east where we see a vast expanse of diffuse emission. At present, they see the exciting star outside the boundaries of the neutral cloud and suggest that the star may have come into existence at the edge of the cloud. Currently, the exciting star is ionizing the nearest part of the neutral cloud ahead of the elephant trunk and in the northwest extension.

The ionization front is advancing in a direction roughly perpendicular to the line of sight, where it is “slowly eating its way” into the dense neutral medium with a velocity on the order of 0.03 km/sec. From the ionization front, ionizing matter is streaming away with a velocity on the order of a few tenths of a kilometer per second, becoming slower the farther it is away from the front. At present the star does not appear to be loosing mass at a high rate, but the shock front may indicate a stronger activity in the past. Deharveng now thinks that the star must be presently ejecting material if we want to see the shock. But observations are needed to be certain.

The absence of any strong infrared sources (which would indicate star formation in opaque dust clouds) and other data suggest that stars are not being born in or near NGC 1491. But Deharveng cautions that there are no recent infrared observations of this region, telling us things about star formation. “A look at the 2MASS images ( JHK nearIR bands),” she says, “shows several red stars in the direction of the nebula, but it is difficult to say if it is due to extinction or to an infrared excess (link to an envelope or a disk). Mid IR observations are needed to say more about star formation.”

To find this little wonder, use the chart on page 68 to find Lambda (l) Persei, then switch to the chart on this page. From Lambda, move your telescope 40⁰ northnortheast to roughly 7th-magnitude Star a, then 30⁰ north-northwest to 7.5-magnitude Star b. NGC 1491 is only 40⁰ west-southwest of Star b and 20⁰ northwest of a pair of 9.5-magnitude stars (c).

I could see the 11th-magnitude exciting star and its brightest emission to the west immediately at 33^ in the 5-inch under a dark sky. The bright horns northwest of the exciting star appear as a highly condensed elliptical patch, while the western and southern extensions appeared less definite (though still obvious), looking like a wider and less-condensed skirt of light; so it looked like an uneven mustache.

These two bright patches (~3⁰ in length) are surrounded by a very faint and highly elusive haze that extended to about 6⁰ on a side. I couldn't detect any of the much fainter nebulosity sweeping far away to the east as some photos show. Still, seeing this fainter 6⁰-wide envelope in the 5-inch gave me hope that larger instruments with wider fields of view might be able to take in more of this very expansive nebula.

Yet when I looked at NGC 1491 through Larry Wood's 12-inch reflector at the George Moore Astronomy Workshop near Edmonton, Alberta, I was surprised to see more or less the same detail that I picked up in my 5-inch – only much more pronounced. Also, the shape of the nebulosity was more clearly defined, with the northwestern horns

being more enhanced, while the southern extension seemed separated from the northwestern emission by a dark lane. This rift of darkness was in the place of the “elephant trunk,” though I couldn't see any bright rim.

Through the 5-inch, the nebula takes power moderately well, and I found that 94 was near the maximum useful magnification. The views at 60^ and 94^ did not bring out any finer features in the nebula (just enhanced the view) but the increase in magnification did bring out some fainter stars in and around the nebula. So take your time with this celestial cloudscape, and see if you can visually dig up some of its more intricate details.

ngc 1514 is a subtle but fascinating planetary nebula in the northernmost reaches of Taurus the Bull, about 3½^{^} eastsoutheast of 3rd-magnitude Zeta (z) Persei in the Hero's eastern foot. This 9th-magnitude star surrounded by a dim halo of nebulosity has long been considered a visually troublesome object. The late deepsky expert Walter Scott Houston once noted that some observers considered it a difficult object for an 8-inch.

While the planetary's central star can be spied with a 2-inch telescope, seeing the 2⁰ -wide nebulosity is a different story. I know I've had my problems with it. I don't recall ever having successfully seen it through the 9-inch f/12 Alvan Clark refractor at Harvard College Observatory in light-polluted Cambridge, Massachusetts. And I've had some unconvincing views through my 4-inch Tele Vue refractor under dark Hawaiian skies: I thought I could see a dim collar of light around the central star, but I couldn't convince myself it wasn't starlight shining through moisture in Earth's atmosphere. My first definite views of NGC 1514's nebulosity came in November 2009, when I decided to try once again, this time with the 5-inch. I was amazed at what a difference 1 inch of aperture made in bringing out the nebula with distinct clarity.

Not surprisingly, NGC 1514 went unnoticed until November 30, 1790, when the great German-born English astronomer William Herschel encountered it during one of his slow and meticulous sweeps of the heavens with his speculum reflector. One can only imagine the great surprise Herschel received when he saw this mysterious object: a bright star “with a faint luminous atmosphere of circular form, about 3⁰ in diameter.” Herschel had never seen anything like it before.

Prior to this discovery, Herschel and his contemporaries believed nebulae were simply clouds of unresolved suns, like the naked-eye appearance of the Milky Way. But Herschel saw NGC 1514 as a “most singular phenomenon! . . . The star is perfectly in the centre, and the atmosphere is so diluted, faint, and equal throughout, that there can be no surmise of its consisting of stars; nor can there be a doubt of the evident connection between the atmosphere and the star.”

NGC 1514 convinced Herschel that the nebulous matter surrounding stars in his planetary class (IV ) were not unresolved clusters. If the cloud and the star are connected, Herschel reasoned, the nebulosity could not consist of very remote and unresolvable suns because the central star is visible. In other words, Herschel found it inconceivable that the central star would burn so brightly as to outshine all the other suns comprising the nebula. Herschel surmized that either the luminous central object is not a star, or that the nebula is not of a “starry nature.”

He accepted the latter sentiment, postulat-ingthatthenebulaconsistsofa“shiningfluid of a nature totally unknown to us . . . since the probability is certain not for the existence of so enormous a body as would be required to shine like a star of the 8th magnitude at a distance sufficiently great to cause a vast system of stars to put on the appearance of a very diluted milky nebulosity.”

In 1864, English amateur astronomer William Huggins (1824–1910) found the first clue to the true nature of planetary nebulae in the spectrum of NGC 6543 (Caldwell 6), which was that of a luminous gas and not that of a haze of unresolved suns. So when we look at NGC 1514 we are seeing the object that led our astronomical ancestors down a new path of thinking – one that began in the late eighteenth century with William Herschel.

Today we know much more about the physical nature of planetary nebulae, and NGC 1514. In a 2003 Astronomical Journal (vol. 126, pp. 2963–2970), C. Muthu and B. G. Anandaro (Physical Research Laboratory, Ahmedabad, India) discuss the results of their spectroscopic studies, which helped them to determine a three-dimensional model of NGC 1514. The nebula has three basic structures: a faint outer shell, an inner ellipsoidal shell titled with respect to the observer, and nearly symmetric bright blobs embedded inside along the polar axis (in the northwest and southeast directions), which is nearly on the sky plane.

The authors note, however, that the blobs do not conform to bipolar morphology. “The large velocity dispersion across each blob shows that the blobs are not collimated,” the authors say. In order to form a bipolar planetary nebula, an equatorial disk is essential to collimate the subsequent ejections toward the polar directions, and NGC 1514 lacks one. Instead, the researchers argue that the nebula is a descendant of a common envelope binary system. In such a system, it's possible that polar blobs or jets can form by the companion's mass transfer to the progenitor at the end of the common envelope phase. “These blobs can be poorly collimated as a result of the possible large size or even the absence of an equatorial disk” the researcherssay,addingthatNGC1514'spolar blobs could have formed in a similar way.

NGC 1514's central star has long been an object of intense study. It differs greatly from other planetary nebulae nuclei in that it is very bright (9.3 magnitude) and, as mentioned, is suspected of being a binary system with an orbital period of about 10 days, and a progenitor mass of

• 4.5 Suns. In a 1997 Publications of the Astronomical Society of the Pacific, Walter Feibelman (NASA-Goddard Space Flight Center) shared that International Ultraviolet Explorer satellite spectra of the star reveal that it consists of a bright type A star (BDþ30^{^} 623) and a very hot O subdwarf companion. The system is enigmatic, having unexplained variations in brightness and a weak P Cygni profile – a combination of spectral features that indicates an outflow of material in the form of either an expanding shell of gas or a powerful stellar wind.

A rotating central binary system would also help to explain the mirrored symmetry of the planetary's two tilted shells. Interestingly, in a 2010 Monthly Notices of the Royal Astronomical Society (vol. 402, pp. 1307–1312), Binil Aryal (Tribhuvan University, Nepal, and Innsbruck University, Austria) and colleagues report their discovery in Infrared Astronomical Satellite (IRAS) data of a huge (8.5 light-year) dust emission region around NGC 1514 as well as two giant (7 and 3 light-year) bipolar dust emissions structures centered on the visible nebula and star. The researchers suspect that each of these regions is physically connected to the planetary nebula, noting that the bipolar structures are slightly tilted with respect to each other, possibly due to precession.

These structures could be associated with the proto-planetary nebula – the transition phase between a spherically symmetric asymptotic giant branch star and an aspherical planetary nebula. The total mass (dust and gas) of all the newly found structures is about 2.2 Suns. “We argue that NGC 1514 and its dusty surroundings represent one of the very few known cases where the preserved history of all main mass-loss phases of a star of intermediate initial mass can be seen,” they say.

To find this intriguing nebula and bright central star – one of the few that can be seen in a decent pair of 10 ^ 50 or larger binoculars under a dark sky – use the chart on page 73 to find Zeta (z) Persei, then 5.5-magnitude Psi (c) Tauri, 4^{^} to the southeast. Depending on your sky and eyesight, you may need binoculars to confirm this latter star; note how it is the northernmost

member of a roughly 3^{^} curve of three similarly bright stars oriented north–south. Once you confirm Psi Tauri, center it in your telescope and switch to the chart on this page. From Psi Tauri make a slow 1¼^{^} sweep due north to the solitary 8th-magnitude Star a. Now look 40⁰ to the northeast for a roughly 20⁰ -wide right triangle of 8.5-magnitude suns. The western side of that triangle should have a 9.4-magnitude sun between the northern and southern points. This is NGC 1514. In other words, NGC 1514 lies midway between two 8.5-magnitude stars, about 20⁰ apart and oriented north-northwest–south-southeast.

At 33^ in the 5-inch, NGC 1514 appears as a subtle amorphous haze tightly wrapped around an easily seen central star. The nebula is quite discernible with averted vision, especially if you compare NGC 1514's appearance to those of the two flanking 8th-magnitude suns, which don't show any glow. The nebula intensifies at 60^, showing a well-defined circular form out to at least 2⁰ all around, and perhaps even a bit further out. The nebula is bright enough to be viewed at 180^ but I find the best and most comfortable view in the 5-inch at 94^.

At this power, the inner shell is most prominent, appearing obviously mottled. With time and averted vision, I can clearly see two prominent arcs of light along the outer edge of the inner shell ~1⁰ out to the northwest and southeast; the southeastern arc is the brighter of the two. Perpendicular to these arcs are fainter elliptical lobes. These features are surrounded by a circular collar of dim light. By the way, an OIII filter really helps to bring out the arcs and other subtle details in the inner shell.

Enjoy!

P erseus is home to several bright and delightful open star clusters: M34, NGC 869 and 884 (the Double Cluster), and Melotte 20 (the Alpha Persei Moving Group). Its boundaries also harbor some fainter, though equally marvelous deepsky wonders, such as planetary nebula M76, lenticular galaxy NGC 1023, and the tiny reflection nebula NGC 1333 (Hidden Treasure 15).

Like NGC 1333, our target NGC 1579 is an irregularly mottled reflection nebula lying in a dark lane relatively near 3rd-magnitude Zeta (z) Persei (Atik) in the eastern foot of the Hero. NGC 1333 lies about 5¼^{^} east-southeast of that star, while NGC 1579 is about 8^{^} to the eastnortheast of it. In physical space, however, the two nebulae are “miles apart”: NGC 1333 lies about 1,100 light-years away, while NGC 1579 is nearly twice as distant.

In 1917, Francis G. Pease used the 60-inch f/5 reflector atop Mount Wilson in Southern California to image this little visual dynamo, which was one of several objects he selected whose “real nature was unknown or those which possessed curious or questionable characteristics.” His photographs of the bright central region of NGC 1579 revealed the nebula's curious dark lanes which, he said, “call to mind the Trifid nebula” – thus the object's modern moniker, the Northern Trifid. The nebula's more expansive and dimmer outer regions, though, reminded Pease of the Orion Nebula, namely it being a large bulbous swath of mottled light marred by dark webs of dust.

Interestingly, direct photographs do not show any nearby bright stars that could be the illuminating source of the nebula. Pease did note that directly south of a broad and prominent arrowhead of dark material – one adjoining the principal dark lane on the north and pointing due east – is a very faint star. In 1956, George Herbig, using a spectrograph on the 36-inch Crossley reflector at Lick Observatory, found Pease's star (magnitude 16) to be very red, having a remarkably high hydrogen-alpha emission and an unusual emission-line spectrum. Subsequent observations showed that the spectra of the star (designated LkHa 101) and the nebula are identical; thus LkHa 101 is responsible for the illumination of NGC 1579.

Although Sharpless (1959) catalogued the nebula as an HII region (S-222), it has no characteristic HII emission lines in its spectrum. Sharpless was obviously misled by the fact that the nebula's image appears so much brighter on the red Palomar plates than it does in the blue. A visual inspection of modern wide-field color images of NGC 1579 can be equally deceiving. They show the nebula as a colorful menagerie of beautiful shades of gunsmoke blue, peach, melon, orange, and rust. But these warmer hues are not due to the excitation of hydrogen gas by ultraviolet radiation streaming from nearby hot stars, but owe their redness to interstellar extinction and to the nature of its illuminating source. The extinction is caused by a vast cloud of dust (L1482) belonging to the Taurus–Auriga Cloud complex – a line of sight that also passes through the more distant Perseus OB2 Association.

Today we know the nebula to be a dusty star-forming region. In a 2004 Astronomical Journal (vol. 128, p. 1233), Herbig and his colleagues note that infrared and radio observations of LkHa 101 suggest that it is a hot star about 8,000 times more luminous and 15 times more massive than the Sun surrounded by a small HII region, both inside an optically thick dust shell. The star appears to be in an interesting phase of its early evolution, being a transition object – one between an optically inaccessible massive star forming deep within its dark and dusty natal cloud and a zero-age, main-sequence star (one that just evolved onto the main sequence) whose radiation and winds have cleared out the dusty neighborhood making it dimly accessible at optical wavelengths.

Although LkHa 101 is heavily obscured by dust (by about 10 magnitudes), it's still the brightest member of a young cluster of stars that contains 35 much fainter hydrogen-alpha emitters (all still embedded in the dusty cloud) with a median age of about 0.5 million years. The cluster also contains at least five bright B-type stars, presumably of about the same age.

To find this intriguing object, first use the chart on page 78 to locate Zeta (z) Persei, then look about 6^{^} northeast for 5th-magnitude 54 Persei and center it in your telescope at low power. Now, using the chart on page 81 as a guide, move 1^{^} northeast to a pair of roughly 7.5-magnitude stars (a), then make another 1^{^} sweep due east to a solitary 7.5-magnitude sun (b). NGC 1579 is a little more than 10⁰ due east of Star b.

In the 5-inch at 33^ the object is a dim sight – a milky smudge barely visible with

averted vision, spanning about 6⁰ in its longest extent to the north. (But don't despair, Christen Luginbuhl and Brian Skiff say that they saw NGC 1579 “easily at low power” through a 6-inch telescope!) Indeed, I found that with time and averted vision, the nebula becomes more and more apparent, especially since a nearby magnitude-12 star to the north helps to focus attention. The nebula has a somewhat delta-wing shape with three irregular extensions to the south (with the middle one being the longest). I also spied what might be the central dark rift, the one that contains LkHa 101 (though it is too dim to see).

At 60^, I saw a roughly 13th-magnitude star pop into view east-southeast of the 12th-magnitude star. The central mass of nebulosity becomes almost rigidly round with a dim snowy beard of fainter nebulosity extending to the southeast toward a roughly 12.5-magnitude star. The nebula did not appear any more dramatic at higher powers, so I found 60^ the best view in my small scope. With time and averted vision, the core can be seen as a bright nebulous concentration, though the dark lane disappears at this power. Interestingly, I did not see much more detail when I viewed the nebula through Larry Wood's 12-inch reflector at the George Moore Astronomy Workshop near Edmonton, Alberta. The glow was much brighter, and very obvious, but it had a round and distinct cometary form, with a strong central concentration surrounded by a circular diffuse halo.

Indeed, in a 1974 Publications of the Astronomical Society of the Pacific (vol. 86, p. 813), Martin Cohen (University of California, Berkeley) notes that NGC 1579 and LkHa 101 may represent a more-massive and more-luminous example of a typically smaller cometary nebula (see Secret Deep 32 (NGC 2316)).

I f you sweep your binoculars across the length of Taurus the Bull under a clear dark sky, you'll encounter a number of star clusters: the famous Pleiades (M45), Hyades (Caldwell 41), NGC 1647 (Hidden Treasure 27), and NGC 1807 and 1817 (Secret Deep 15 and16).Let's,forthemoment,also include the large 45⁰ -wide NGC 1746, a highly neglected object about 10^{^} northeast of Alpha (a) Tauri (Aldebaran) and 1^{^} southwest of 6th-magnitude 103 Tauri.

All these young objects lie very close to the point directly opposite the Galactic center, in the direction of the Taurus dark clouds – a 4-million-year-young complex with a mass of some 6,500 Suns. It is a beautiful region of solar-mass star formation riddled with stunning dark nebulae, Herbig– Haro objects, and other enigmatic young stars. At a distance of some 570 light-years, the Taurus dark cloud complex is one of the nearest to the Sun, placing the Hyades in the foreground and the Pleiades partially immersed into the cloud's front edge.

The other clusters mentioned are all highly reddened background objects, with the amount of dimming dependent on the density of the obscuring clouds. Of them, NGC 1746 is especially intriguing, since it is not only an historical curiosity (as well as a highly neglected visual target), but also an object that is fast attracting the attention of modern astrophysicists. But let's first look at NGC 1746's history.

On the evening of November 9, 1863, German astronomer Heinrich Louis d'Arrest (1822–1875) was using the 11-inch f/17.5 Merz refractor at Copenhagen Observatory to observe H VIII-43 (GC 970 ¼ NGC 1750),

which William Herschel had discovered on December 26, 1785. After d'Arrest observed this “poor cluster,” he determined its position, placing it about 10⁰ north of Herschel's, but he still referred to it as H VIII-43.

In his 1888 General Catalogue, however, John Louis Emil Dreyer mistook d'Arrest's new position for a new object, listing it as GC 5349 (NGC 1746). Interestingly, on the same night Herschel discovered H VIII-43, he swept up another new cluster in the same region, H VII-21, which Dreyer listed as GC 977 ¼ NGC 1758. As plotted above, you can see how the three open clusters overlap, with NGC 1758 abutting NGC 1750 immediately to the northeast, while both NGC 1750 and NGC 1758 are superimposed on larger (45⁰ ) NGC 1746.

In time, the reality of some of these clusters was questioned. Indeed, Harvard astronomer James Cuffey had mentioned only NGC 1746 in a 1937 Harvard College Observatory tercentenary paper on Galactic clusters (Annals of Harvard College Observatory, vol. 105, no. 21). Since then, and until recently, NGC 1750 and NGC 1758 have remained largely historical footnotes; in fact, I am not aware of any modern star chart showing these two clusters.

But the tides have turned. In a 2003 Baltic Astronomy (vol. 12, pp. 323–351), Vitautus Straizys (Vilnius University, Vilnius, Lithuania) and colleagues explain how their photometry, on 420 stars down to visual magnitude 16 in the region, found NGC 1750 and NGC 1758 to be two separate and real clusters at the same mean distance of about 2,500 light-years. These findings support their earlier study in 1992 that had similar results.

Furthermore, Spanish astronomer David Galad´ı-Enr´ıquez (University of Barcelona) and his colleagues concur. In a 1998 Astronomy & Astrophysics (vol. 337, p. 125), the researchers conclude that the mutual separation, relative velocity (they found the presence of two stellar populations in the region with somewhat different directions of motion), and age difference of NGC 1750 (200 million years) and NGC 1758 (400 million years) led them to agree that these are two physically independent clusters. The distances to the clusters, they found, are 2,050 light-years for NGC 1750 and 2,480 light-years for NGC 1758. The researchers also provided the more accurate cluster coordinates given in the table above.

As for NGC 1746 – a small clump of stars that d'Arrest positioned 10⁰ north of NGC 1750, none of the modern research supports the existence of a real object inthe area. One can only imagine that d'Arrest either made an error in his declination measurement, or that he mistook this rogue clump of milky starlight for Herschel's VIII-43. Remember, it was Cuffy in 1937 who abolished NGC 1750 and NGC 1758 from the records and reassigned NGC 1746 to an erroneously large cluster in the area: the one that exists on most (or all) modern star charts. In fact, in a private 2010 communication, Galad´ı-Enr´ıquez said, “I think that the research by Straizys et al. and by our group definitively clarify the structure of this area in Taurus, and NGC 1746 should be taken out from the list of galactic open clusters.”

The modern resolution to the NGC 1746 field mystery also solves another age-old conundrum that the late deep-sky expert Walter Scott Houston loved to ask: What is the apparent diameter of NGC 1746? Houston noted that estimates ranged from 25⁰ to 1^{^} . Now we know the answer.

The fact is, a true cluster exists at Herschel's positions for both H VIII-43 (NGC 1750) and H VII-21 (NGC 1758). Thus, of the three objects – NGC 1746, NGC 1750, and NGC 1758 – only NGC 1746 has been erroneously assigned (meaning, it doesn't correspond to a true cluster)! The modern portrait of the region (see the illustration below based on Straizys et al.'s 1992 work), then, shows the presence of two overlapping open star clusters, possibly seen in the act of penetrating one another. NGC 1750 is the more massive of the two, equaling some 10,000 Suns.

To find these twin delights, I suggest first hunting down the region with binoculars.

Look about 10^{^} northeast of Aldebaran, in a line with Beta (b) Tauri (Alnath), the tip of the Bull's southeastern horn. In 10 ^ 50 binoculars under a dark sky, the region including NGC 1750 and NGC 1758 appears as a 50⁰ -wide patch of milky starlight, like an isolated star cloud with bright and faint stars that shines around 5th magnitude. (It can also be seen with averted vision and the unaided eyes.)

This region hugs a 20⁰ -long Y-shaped asterism of roughly 8th-magnitude suns (oriented northeast–southwest) about 1^{^} southwest of 6th-magnitude 103 Tauri. With averted vision, NGC 1750 becomes apparent as a smaller, isolated patch of starlight, 30⁰ -wide, just west of the Y's stem. It has a more delicate luster than its brighter neighbor NGC 1647 some 6^{^} closer to Aldebaran. NGC 1758 on the other hand appears only as a small suggestion of hazy light tucked into the open end of the Y; you need extremely dark skies to “sense” it in handheld binoculars.

In the 5-inch at 33^ and a nearly 2^{^} field of view, the two clusters appear as a warped peanut of irregularly bright suns,

with a major axis oriented roughly northeast–southwest. The stars seem to bloom out of the Y-shaped asterism like two polyps of starlight; these are a mixture of true cluster members and field stars, but don't worry about that, just enjoy the view. Look for a prominent gathering of about a dozen stars in NGC 1750, which form a roughly 8⁰ irregular circle of starlight, whose center lies about 6⁰ northwest of the Y's stem.

Two wide pairs of roughly 10th-magnitude suns jut beyond this stellar ring: one pair to the west-northwest (oriented west-northwest to east-southeast), and the other pair to the west-southwest (oriented northeast to southwest); these pairs define the true western boundary of NGC 1750. The stars in the direction of NGC 1758 appear more congested and compact and congregate just southwest of the two stars at the open end of the Y. Most apparent is a fine pair of suns toward the northeast end of the cluster.

Long spidery filaments of field stars extend the true cluster boundaries in all directions in this rich Milky Way region. The clusters truly do, however, look best at low power. But they will also stand scrutiny at higher magnifications. I especially enjoyed looking at NGC 1758 at 94^, which brought out some fanciful arrangement of dim suns that seemed to loop and curl in haphazard directions, depending on how I mentally “attached” the suns. The clusters also have a fair share of tight pairs and tiny triangular arrangements of stars.

With time, these loose clusters become quite distinct, and it's not hard to imagine one interacting with the other. So take your time and enjoy this view of two clusters literally passing through one another.

O rion is chock-full of deep-sky wonders. Every veteran observer has tackled the constellation's “big three” nebulae: M42 (the Great Orion Nebula with its famous Trapezium of stars), M43, and M78. My Hidden Treasures list added eight more visual delights in Orion: open star clusters Collinder 69 and 72 and NGC 2169; the nebulae NGC 1977, 1981, 1999, 2024, and 2163, and several other “celestial hors d'oeuvres” near the Belt star Zeta (z) Orionis.

Although the small but obvious reflection nebula NGC 1788 didn't make it to the final Hidden Treasures list, I did consider it. This isolated patch of glowing gas and dust lies nearly 7^{^} west-northwest of M42 and the young, hot stars that make up the heart of the Orion OB1 Association. You'll find it just above the northeastern border of Eridanus, only about 1½^{^} northnorthwest of 3rd-magnitude Beta (b) Eridani.

In the standard scenario of triggered, or induced, star formation, ultraviolet radiation streaming out from hot, young OB stars, or shock waves expanding out from supernovae explosions, compress the cold material in giant molecular clouds. Consequently, dense cores form and collapse in the cloud due to self-gravity, forming embryonic protostars in the process. As each new

stars in the universe cannot be fully explained if stars only form in large clusters. “Thus,” they say, “effective star formation in isolated molecular clouds, far from the massive complexes but most likely still induced by them, offers an explanation for the observed distribution of stars.” The region around NGC 1788 is one such isolated cloud. “Although this ghostly cloud is rather isolated from Orion's bright stars,” they explain, “the latter's powerful winds and light have had a strong impact on the nebula, forging its shape and making it home to a multitude of infant suns.”

Energy streaming from the bright, massive stars belonging to the vast stellar groupings in Orion has also caused hydrogen gas in the region to glow, creating a long wing of matter east of the main reflection nebula – the part we see most prominently through our telescopes, which is mottled with “furry-looking” dust (Lynds 1616). Seen together with a short vertical segment of reflection nebulosity northwest of the main nebula, NGC 1788 looks like a fantastic bat in flight, darting on the feed (see the European Southern Observatory image above).

A 2010 ESO press release notes that all of the stars in the NGC 1788 region have an average age of only a million years. These “preschool” stars fall naturally into three well-separated classes: (1) the more senior stars lie east of the long wing; (2) moderately young ones make up the small cluster enclosed in the main nebula which they illuminate; and (3) the youngest suns, still embedded in their natal, dusty cocoons (those visible only at infrared and millimeter wavelengths), lie further to the west. The segregation of stellar groups suggests that a wave of star formation, generated around the hot and massive stars in Orion, propagated throughout NGC 1788 and beyond.

Telescopically, NGC 1788 is a small but pleasing reflection nebula that appears more extensive at lower power than at high power. To find it use the chart on page 87 to locate 0-magnitude Beta (b) Orionis (Rigel), the left knee of Orion, then 3rd-magnitude Beta Eridani 3½^{^} further to the northwest. Beta Eridani marks the southern apex of a 40⁰ -wide isosceles triangle with the 5th-magnitude stars 66

and 68 Eridani. Center 68 Eridani in your telescope at low power, then switch to the chart on this page. Now follow the roughly 1^{^} -long line of 7th- to 9th-magnitude stars that flows northward from 68 Eridani. Begin the search along this line by moving 20⁰ north-northwest to 9th-magnitude Star a and stop when you get to 8th-magnitude Star b. NGC 1788 lies only about 25⁰ to the west-southwest of Star b.

The brightest part of the nebula lies southeast of a 10th-magnitude star (HD 293815) that marks the southwest corner of a 10⁰ -wide Trapezoid of similarly bright suns (c). HD 293815 is actually the brightest member of a dim cluster of suns in NGC 1788; the cluster aspect, however, is lost to the eye when seen through small backyard telescopes, though it is often revealed glamorously in images.

With direct vision at 33^ in the 5-inch, NGC 1788 appears as a fuzzy stellar-like the outer halo looks off-center.

At 60^, dark dust (Lynds 1616) near HD 293815, which streams through the southwestern part of the nebula, caused my eye to see variations in the reflection nebula's brightness, but I couldn't perceive any definite structures – just ghostly shadows that wafted in and out of view. Small nebulous

knots of dim stars also appeared superimposed on the cloud, though these too were difficult to define. The nebula is much more difficult to see in my modest scope at 94^, though it does show HD 293815 as a clear, blazing star, and a dim 11.5-magnitude sun embedded in the southeastern nebulous knot.

ngc 1807 and 1817 are two intriguing patches of starlight in Taurus that form a visual double cluster at the northern tip of Orion's Shield. William Herschel discovered the larger and fainter cluster (NGC 1817) in February 1784. What he apparently did not notice is the brighter and slightly smaller gathering of suns (NGC 1807) 25⁰ to the southwest; his son John catalogued that object. Interestingly, while, NGC 1807 is 0.7 magnitude brighter than NGC 1817, it is the less visually obtrusive, containing only 37 members in an area 12⁰ across. NGC 1817, on the other hand, contains more than 280 members (most being fainter than 12th magnitude) spread across 20⁰ of sky.

Then again, the “double” aspect of the cluster may just be an illusion. In a 2004 Astronomy & Astrophysics (vol. 426, p. 819), Spanish astronomer L. Balaguer-Nu´ n˜ez (Barcelona University) and colleagues calculated proper motions for, and reevaluated the membership probabilities of, 810 stars in the area of NGC 1817 and NGC 1807. Of those, the researchers found 169 probable members in what appears to be only one very extended physical cluster: NGC 1817. Thus, John Herschel's paltry NGC 1807 may just be part of a larger and very extended cluster.

Indeed, in a 2003 Astronomy & Astrophysics (vol. 399, pp. 105–112) J.-C. Mermilliod and colleagues confirmed members out to a distance of 27⁰ from NGC 1817's core, doubling its previous radius. NGC 1807/ 1817, then, can be viewed as a single cluster nearly 1^{^} across in the sky, perhaps with dual cores. Seen this way, NGC 1807/1817 has the same apparent diameter (and separation between the two cores) as the Double Cluster in Perseus.

But at an estimated distance of 5,900 light-years, NGC 1807/1817 is 1,400 light-years closer, giving it a true physical extent of about 100 light-years, or about 30 light-years smaller than the Double Cluster in Perseus. NGC 1807/1817 is an intermediate-aged cluster and probably formed between 0.5 and 1 billion years ago from the same cloud of dust and gas in the Galaxy's outer Perseus arm, directly opposite the Galactic bulge. NGC 1807/ 1817 then is in the same age group as the neighboring Hyades (650 million years): The Perseus Double Cluster, by comparison, is a mere 13 million years young.

In a 2009 Astronomical Journal (vol. 137, pp. 4753–4765), Heather R. Jacobson and her colleagues found NGC 1817 to have about the same amount of iron (per unit of hydrogen) as does the Sun. But she says that follow-up spectroscopy of 30 confirmed cluster members has revealed a lower metal abundance: about two-thirds the amount found in the Sun. Other studies found that its color–magnitude diagram also shows a well-defined main-sequence turnoff region, and a populous red-giant clump (one about 0.15 magnitude bluer than the Hyades giants, suggesting that NGC 1817 may have a slightly lower heavy-element abundance).

The cluster also has a lot of variable stars (27). Most interesting are the 17-odd d Scuti stars, which Danish astronomers M. F. Anderson and T. Arentoft (Aarhus University) and their colleagues say makes NGC 1817 the most abundant cluster in this type of stars. Delta Scuti stars are of spectral type A to F and have masses ranging from 1.5 to 2.5 Suns. They lie at the bottom of the classical Cepheid instability strip (narrow, vertical region in the Hertzsprung–Russell diagram, between the high end of the main sequence occupied by stars more massive than the Sun and the giant branch). Delta Scuti Stars, then, are pulsating stars in a post-main-sequence stage of stellar evolution. They show multiperiodic signals with periods on the order of 0.25 to 5 hours, and display light variations of less than 1 magnitude. For NGC 1817 the turnoff from the main sequence, due to exhaustion of hydrogen in the core of stars, is located inside the instability strip.

To “fish” up this interesting solo/duet, John Herschel suggested “carrying a line from the foremost star in Orion's belt, Mintaka, though Bellatrix, and there intersecting it by another from Aldebaran, due east towards gamma Geminorum.” Otherwise, use the chart on page 92 to follow Orion's Shield northward to the 5th-magnitude stars 11 and 15 Orionis; you'll also find them about 7½^{^} east and a bit south of Alpha (a) Tauri (Aldebaran) in the Hyades. Now use the chart on this page to locate 5th-magnitude Star a, about 40⁰ northeast of 15 Ori. Under dark skies, I can see NGC 1817 in 10 ^ 50 binoculars as a distinct fuzzy glow 40⁰ northeast of Star a. NGC 1807 pops into view with a bit more concentration.

W

Together, the clusters will be difficult to appreciate in small telescopes under bright skies. Admiral William Henry Smyth called NGC 1817 “A very delicate double star preceding a tolerably condensed cluster.” He saw a yellow primary and a blue secondary. The pair, he said, is an “outlier of a rich gathering of [faint] stars, which more than fills the field, under an estimation of 20⁰ or 25⁰ of diameter, but he did not notice the pair here measured. However, Sir John Herschel thus describes it, No. 349: “large rich cluster; stars 12 to 15 magnitude; fills field. Place that of a double star. The most compressed part is

• 42.5 seconds following the double star, and 3⁰ south of it.”

At a glance at 33^ in the 5-inch, NGC 1817 and 1807 appear as two separate lines of stars. But in averted vision, NGC 1817 suddenly swells as a wide wash of stars that flows off that line to the northeast. With time, fainter stars also pop into view to the west-southwest of NGC 1807. Both clusters have long tails of starlight that seem to attach the clusters to Star a, like strings to balloons. If you slightly defocus the view, the region separating the two clusters looks like a 20⁰ -wide V-shaped black lagoon – as if some divine power had driven a wedge into the cluster in an attempt to rip it apart.

At 60^ and 94^, NGC 1807 is a sparse aggregation of more than two-dozen suns that make up a doll-like stick figure: a prominent line of stars oriented northwest-southeast forms the doll's spine, a wide pair of stars at the southeast end form the legs, and a solitary star at the

north end marks the head. The arms cross the spine from the northeast to the southwest. Note too the pretty triad of stars at the midpoint of the doll's spine.

At these same powers, NGC 1817isa more dynamic grouping of irregularly bright suns spread across 20⁰ of sky. It contains four bright stars that shine between 9th-and 10th-magnitude and form a short lightning-bolt pattern oriented northwest–southeast. With averted vision, the east-northeast side of NGC 1817's lightning bolt swells into a ball of noisy starlight. Some two-dozen suns cram into a roughly 10⁰ -wide ellipse of fuzzy starlight.

Now return to low power and relax your mind. Doyou see the long and looping arms that seem to stream away from each cluster fragment, visually extending their boundaries across nearly 1^{^} of sky? Remember, many of the stars you see here in this region actually belong a single cluster; the double aspect is most likely only an illusion. Still, expert deep-sky observer Steve Coe of Arizona likes to call the two cluster fragments the Poor Man's Double Cluster.

Secret Deep 22 & 23 (NGC IC 417 & NGC 1931)

T ake the time to study a wide-field photograph of, or turn your binoculars to, the rich Milky Way region around the bright open star clusters M36 and M38 in Auriga the Charioteer. Two curious threads of starlight seem to connect M36 to M38, and M38 to 5th-magnitude Phi (f) Aurigae, an orange K-class giant flanked some 10⁰ on a side by two 6th-magnitude attendants. As a whole, this star-and-cluster stream forms an open V, like the fleshy flower of a calla lily.

As seen through binoculars, New York City skywatcher Ben Cacace refers to the latter star stream as the Cheshire Cat asterism – referring to the lingering smile that belongs to the fictitious cat in Lewis Carroll's 1923 children's classic Alice's Adventures in Wonderland. The smile begins just 30⁰ south-southeast of M38, at the 7th-magnitude variable star LY Aurigae, then arcs 1^{^} south-southwest to Phi Aurigae, and ends 30⁰ further to the southwest at another 7th-magnitude sun with an 8.5-magnitude companion. The cat's eyes are two 6.5-magnitude stars: one 30⁰ southwest of M38, and the other about 42⁰ south-southwest of it.

More impressive is the same 2^{^} region seen at low power in a rich-field telescope. When I first observed it through the 5-inch at 33^, Phi Aurigae immediately captured my attention. That crisp golden star has numerous fainter stars sprinkled across it linearly from the northeast to the southwest. Equally appealing, however, is a small collection of crisp jewels, 9th-magnitude and fainter, in a 5⁰ -wide region just hugging Phi to the southeast, surrounding three roughly 9th-magnitude suns in a small arc. With averted vision, the region looks like a patch of Milky Way shaped like an inverted V (seen with north up). Unlike other nearby swaths of Milky Way, the region just southeast of Phi also has an added glaze, a frosting of nebulosity that made it appear as if I had accidentally breathed on the eyepiece (but I didn't).

I knew that light from the emission nebula IC 417 washed through this region; I also I knew that it appeared most intense in the region where I suspected seeing it. But I wasn't prepared to spy that small aggregation of suns sparkling between it and Phi Aurigae. None of my star charts showed a cluster in this position, though the Millennium Star Atlas did have one object (Stock 8) plotted about 5⁰ to the west. Since I didn't see any cluster in that latter position, I suspected that Stock 8 must have been misplotted in the Millennium, and it was.

These observations later caused me to reflect on a mysterious historical discovery: one made by Caroline Herschel ( William Herschel's sister and observing assistant) on the evening of October 13, 1782. That night, Caroline spied a “nebula below Phi Aurigae.” It has been proposed that Caroline must have observed one of the bright Messier objects in the region. But M38 is nearly 1½^{^} to the northnortheast. M36 is nearly 2^{^} to the eastsoutheast. And M37 is even further away, some 5^{^} to the east-southeast. The fact is, a nebula and cluster do exist south of Phi Aurigae. Even if Caroline did not see the nebulosity, she could have easily seen Stock 8 as an unresolved glow. Given Caroline's great eye for dim nebulae and comets, why wouldn't she have noticed such a bright and obvious hazy collection of suns?

No matter, Ju¨ rgen Stock at Warner and Swasey Observatory found the cluster while searching blue objective prism plates along the Galactic equator and catalogued it in 1954; it was the eighth of 21 possible new clusters he found based on the spectral class and approximate magnitudes of their stars. He then published the list in a 1954 Astronomical Journal (vol. 59, p. 332).

The nebula around the cluster was discovered by Max Wolf in 1892. Wolf 's plates show the immediate region of Phi Aurigae and Stock 8 covered with the glow. On the evening of March 6, 1902, Wolf also discovered the “Great V” – a larger swath of nebulosity that seems to connect the nebulae IC 417, IC 410, and IC 405, the star clusters M38 and NGC 1907, and the stars 16, 19, and 36 Aurigae. He discovered this “Great Nebula in Auriga” after scanning a five-hour-long exposure he made of the field surrounding Nova Aurigae. The photo, he said, supported the theory that nearly all these stars, clusters, and nebulosity are at the same order of distance from our Earth as in similar cases in Cygnus and Orion.

As for Stock 8, it is indeed embedded in its nascent nebula IC 417. But it's not the youngest object in the region. In a 2008 Monthly Notices of the Royal Astronomical Society (vol. 384, pp. 1675–1700), Indian astronomer Jessy Jose (Aryabhatta Research Institute of Observational Sciences, Nainital) and colleagues found that Stock 8 is a youthful cluster about 8,150 light-years distant. It spans some 23 light-years across and intervening dust dims it by at least 0.5 magnitude. But Two Micron All Sky Survey near-infrared and spectroscopic data have also identified a population of young stellar objects – stars that have evolved past the protostar stage but have not yet reached the main sequence – in the area with ages between 1 and 5 million years; the other cluster stars are around 2 million years.

Many of the young stellar objects lie along a nebulous stream belonging to IC 417 towards the east side of Stock 8. A small cluster was also found embedded in that feature. Both the young stellar objects in the nebulous stream and in the embedded cluster, the researchers explain, are younger than the stars in Stock 8. Thus, it appears that star formation activity in the nebulous stream and embedded cluster may be independent from that of Stock 8. Apparently shocks created by the ionizing sources in (and west of ) Stock 8 have not yet reached the nebulous stream.

Note that the dimensions of IC 417 given in the table on page 98 reflect only its brightest section southeast of Phi Aurigae. In long-exposure photographs, however, IC 417 is a vast cloud of glowing hydrogen gas with long spindly legs that stretch across 1½^{^} of sky. This larger form of IC 417 was glamorized by Boston amateur astronomer Steve Cannistra, who, after looking over one of his marvelous wide-field photos of the region, nicknamed IC 417 “The Spider” and our next target – the tiny (4⁰ ) emission/reflection nebula NGC 1931 (about 50⁰ to the eastsoutheast) – “The Fly.”

NGC 1931 is a beautiful little nebula harboring a tiny cluster that's easily seen in small telescopes. William Herschel discovered this gem in 1793, cataloguing it as a bright nebula (H I-261). In his Cycle of Celestial Objects, Admiral William Henry Smyth calls it a “resolvable nebula” – no doubt in deference to William's Herschel's belief that most nebulae, under sufficient magnification, will resolve into a multitude of suns, just as the naked-eye Milky Way does under even the lowest of powers.

Indeed, Smyth says that William Herschel resolved “one or two stars in the middle, or an irregular nucleus,” while his son John saw a triple star within the nebula which surrounds them like an atmosphere. “With these premonitions,” Smyth continues, “I attacked it under most favorable circumstances. The nebula is situated in a rich field of minute stars, with five of the 10th-magnitude, disposed in an equatorial line above, or to the south, of it, and preceded by a bright yellow 7½ magnitude star in the same direction. After intently gazing, under moderate power, the triangle rises distinctly from the stardust, and presents a singular subject for speculation.”

NGC 1931 is a young and low-mass open star cluster in an extension of the Milky Way's Perseus Arm. The cluster appears surrounded by emission and reflection nebulosity (Sharpless 2-237 ¼ NGC 1931), though in a 1986 study of interstellar reddening across the region, astronomers at Uttar Pradesh State Observatory in Naini Tal, India, found that the nebula is a background object on which the cluster is superimposed. NGC 1931 is 7,000 light-years distant and about 10 million years young, placing it in an age group with NGC 2362 (Caldwell 64), the Tau Canis Majoris Cluster.

In a 2009 Monthly Notices of the Royal Astronomical Society (vol. 397, p. 1915B), Brazilian astronomer C. Bonatto (Univer-sidade Federal do Rio Grande) used Two Micron All Sky Survey photometry data to confirm the age estimate for NGC 1931, adding that the cluster doesn't appear to be in dynamical equilibrium, and either may be evolving into an OB association or is doomed to dissolve into the Milky Way in a few tens of millions of years.

In the 5-inch at 33^, NGC 1931 is the easternmost “star” in a 20⁰ -long, upward curving arc of three 7.5-magnitude suns, oriented east to west. It appears stellar with a direct glance, but swells into a distinct nebulous knot with averted vision. Doubling the power doesn't change much; the nebula continues to appear small (~2⁰ ) and round but with a starlike object at the core. A row of five conspicuous stars (oriented north–south) lies a few arcminutes west-northwest of NGC 1931, which is bracketed by two roughly 10th-magnitude suns oriented in the same direction, so there appear to be two parallel (but offset) rows of stars here, side by side. Increasing the power to 94^, I could see thin rays of nebulosity, but they might also have been faint star streams.

The glow is extremely condensed and takes magnification well. I especially enjoyed viewing the nebula and cluster at powers ranging from 165^ to 330^. At 165^, the nebula is most intense and obvious and has a smooth milky sheen that gradually, then rapidly, fades as I look outward from the bright core. At the higher end of the power scale, the roughly 12th-

magnitude central star becomes a stunning triad of suns attended by three other fainter jewels that swim in and out of view as I move my eye around using averted vision. Seen together, these stars form a marquee diamond. The southern end of the nebula is more condensed than the northern end. I also suspected a graceful sweep of reflection nebulosity stretching southward from the main nebula, but this may be an illusion owing to a nearby star that tends to pull the light in that direction. See what you think.

Secret Deep 24 (Collnder 70 –– Orion's Belt)

Like those three stars of the airy Giants' zone, That glitter burnished by the frosty dark; And as the fiery Sirius alters hue, And bickers into red and emerald, shone

The Princess, Alfred, Lord Tennyson, 1847

W hen i was a child growing up in Cambridge, Massachusetts, it was customary to attend midnight mass on Christmas Eve. On one of those memorable evenings, my friends and I walked the quarter mile or so to Sacred Heart Church in Watertown under a star-filled sky – boots crunching in the snow, cold nipping our cheeks, comets flying from our mouths into the crisp winter air. Naked oaks lined the streets, and their long and skeletal branches formed a complex web through which I could see the brilliant stars of Orion the Hunter flashing in and out of view as we walked. Orion followed us, its giant form stomping across the neighborhood rooftops keeping pace. Suddenly, the Hunter's hourglass body stood boldly before us in a clearing, his narrow waist adorned by three sparkling gems in a row, and we paused. The Belt had captured my friends' attention. Although it was just a moment as fleeting as a shooting star, we each in our own way paid homage to these stars in silent wonder before continuing on.

There isn't a time-honored stargazer who hasn't looked up on crisp winter evenings and marveled at Orion's Belt. This splendid row of three 2nd-magnitude stars, stretching 3^{^} across the velvet night like a string of pearls, culminates in late January (meaning it stands highest above the southern horizon after sunset) and forms the most significant asterism in the winter night sky next to the Big Dipper.

Actually, the Arabic name for the Belt's middle star, Alnilam (1.7-magnitude Epsilon (ε) Orionis), means “the String of Pearls.” The Belt's western star, Mintaka (2.2-magnitude Delta (d) Orionis) is Arabic for “the Belt” and the first to rise above the eastern horizon; early astrologers saw Mintaka's arrival as important, for it portended good fortune. The Belt's easternmost star, Alnitak (1.8-magnitude Zeta (z) Orionis), is Arabic for “the Girdle.”

Orion's Belt is a celestial magnet, one that draws attention to itself and inspires the imagination. Different cultures throughout time have pondered these three celestial wonders and attributed significance to them. Robert Bauval and Adrian Gilbert gave great cosmic importance to the Belt stars in their 1995 book The Orion Mystery (Three Rivers Press, New York), claiming that the Pyramids of Giza are an earthly representation of the three stars as they appeared in the sky around 10,400 BCE. Alas, as Griffith Observatory director Edwin C. Krupp wrote in the February 1997 issue of Sky & Telescope, the orientation of the Belt stars and those of the pyramids simply do not match. Still, it's agreed that the stars of Orion were important to the ancient Egyptians who saw in them their great god Osiris, who not only presided over the life and death of his people, but also the fertile flooding of the Nile. This fact also explains the proximity of Orion (Osiris) to Eridanus (the Nile).

To the Chinese of old, the Belt was a weighing beam. Early Hindus saw its stars as the three-jointed arrow that the hunter Lubddhaka (Sirius) shot into Prajapati (Alpha, Gamma, and Lambda Orionis), the father of beautiful Rohini (Aldebaran). Prajapati had lusted after his own daughter, who cavorted around disguised as an antelope. To win her, Prajapati changed himself into a deer. Realizing this trick, Lubddhaka shot Prajapati with an arrow (the Belt), riveting him to the sky between him and Rohini. To this day, amateurs still find Aldebaran and Sirius by extending Orion's Belt equidistant to the northwest and southeast, respectively.

In Hawaii, the Belt stars were Na kao, meaning “the darts,” (these darts were long poles thrown with both hands); their station on the celestial equator made them a crucial navigation tool during their great Pacific voyages. Hawaiians also believed that when these stars ascended, stormy winds would blow:

Pierced by the three stars of Orion

Are the clouds,

of rain as they drift on

The Rain!

In the April 2001 issue of Natural History, renowned archaeoastronomer Anthony F. Aveni (Colgate University) tells us the significance of Orion's Belt to the Aztecs, who saw in the heavens the sustainers of life – “the gods they sought to repay, with the blood of sacrifice, for bringing favorable rains, for keeping the earth from quaking, for spurring them on in battle.” Among the gods was Black Tezcatlipoca (“smoking mirror”), god of the night, which he ruled from the north. We see him in the sky – in the stars of what we call the Great Bear – hopping around the North Star on his one foot.

On Earth, Tezcatlipoca was a sorcerer and liked to prowl the roads after sunset to surprise tardy travelers. He could appear as a shrouded corpse or a headless man with his chest and stomach slit open; anyone brave enough to rip out his heart could demand a reward for returning it. But Tezcatlipoca wasn't always bad. He later used fire sticks (Orion's Belt) to bring warmth to the central hearth, whose fire ensured the continuation of life. The lighting of the sticks may also be a metaphor for the sexual energy needed to procreate, thus sustaining life on Earth.

Interestingly, in Mayan mythology, Orion's Belt is the center of creation. It's where the paddler gods transported the maize gods in a huge canoe that corresponded to the Milky Way until they arrived at Orion's Belt, which they envisioned as a huge cosmic turtle. Using a lightning stone, the god Chak cracked open the back of the cosmic turtle, from which the maize gods grew. We can see the cracked turtle shell in the ballcourts of the Yucatan, which are long lines like Orion's Belt. In Pre-Columbian times, the ballcourts substituted for observatories that the Maya used to watch the passage of time. Indeed, when Orion's Belt appeared through a designated hole, or the Sun shone directly on a specific spot, it meant spring (the moment of creation/life) was near.

Australian aborigines also, in a way, envisioned the Belt stars as stars of fertility. They saw the three stars as young men dancing to attract the attention of the maidens (the Pleiades). In South Africa they were the three kings or sisters. While in Upper Germany they were seen, among other things, as the Magi – the three wise men who followed the Star of Bethlehem to Christ's birthplace (another fertility symbol).

The Belt of Orion even appears in the Bible ( Job 38:31): After a lengthy debate with Job and his friends, God emphasizes his sovereignty in creating and maintaining the world, asking Job if he has ever had God's experience or authority:

Canst thou bind the cluster of the Pleiades, Or loose the bands of Orion?

In a different vein, to the Chimu Indians of Peru, Epsilon, the central Belt star, was a criminal being held by the arms by two celestial guards (Delta and Zeta Orionis). There they await the Moon goddess to punish the criminal by tossing his body to the four vultures (Alpha, Beta, Gamma, and Kappa Orionis) who will devour him: these stars served as a perpetual reminder to all of the penalty awaiting anyone who follows a life of crime.

Imagine all this attention to the Belt stars, yet no one realized that they belong to an open star cluster until Swedish graduate student Per Arne Collinder listed it as the 70th such object in his 1931 doctoral dissertation “On structural properties of open galactic clusters and their spatial distribution.” Collinder 70 contains

100 members that thread across, or loop around, the three Belt star like a giant serpent. The view is most pronounced in binoculars, which shows some 70 stars at a glance.

I liken the binocular view to the historic Serpentine Column – an ancient bronze column at the Hippodrome of Constantinople (now Istanbul, Turkey). In his History of the Decline and Fall of the Roman Empire, Edward Gibbon describes the column as “the bodies of three serpents twisted into one pillar of brass. Their triple heads had once supported the golden tripod which, after the defeat of Xerxes, was consecrated in the temple of Apollo at Delphi, by the victorious Greeks.”

In true physical extent, this stellar column spans 50 light-years of space. Now lower your binoculars and look at Rigel. All the cluster members lie in the same region of space as this blue supergiant (860 light-years distant). In fact, the three bright Belt stars are all hot giant stars. All are destined to die in a fiery supernova explosion at some unknown date in the future. Let's look at the three Belt stars now in more detail.

Mintaka (915 light-years) is a B-type giant 90,000 times more luminous than the Sun and 20 times more massive; it's also a spectroscopic double, having an O-type companion of similar luminosity and mass. The stars orbit one another every 5.73 days and share a common center of gravity. As the stars orbit, they slightly eclipse each other, causing the “single” star we see with our eyes to vary in brightness by a mere 0.2 magnitude. But if you look at the star with even the smallest of telescopes, you'll see the pale white primary has a bluish 7th-magnitude visual companion only about 1⁰ due north.

In 1904, German astronomer Johannes Hartmann (1855–1936) at Potsdam Observatory found stationary calcium absorption lines in the star's spectrum. Since these lines did not share in the periodic displacements of other spectral lines caused by Mintaka's orbital motion, Hartmann deduced that the calcium line belonged to an intervening absorbing cloud. This discovery helped prove the existence of interstellar matter – the thin but pervasive veil of interstellar gas and dust out of which new stars are born; when stars die, they recycle some of their material back into the interstellar medium. What I find most fitting in Hartmann's discovery is that it involves a star central to the Mayan creation myth.

Alnilam (1,374 light-years) is a B-type supergiant 40 times more massive than our Sun. The star produces mighty winds that flow at speeds up to 2,000 km/sec, while radiating prodigious amounts of ultraviolet light (375,000 solar luminosities) from its 25,000 kelvin surface. The circumstellar environment is so hot that it illuminates a dim and diffuse swath of interstellar gas (reflection nebula NGC 1990, discovered by William Herschel in 1786). This gas is but an enhancement of a much larger cloud of gas and dust that surrounds the entire constellation.

You can spend some time looking for NGC 1990, but beware, while some images show the nebula, many skilled observers using sizable telescopes have been frustrated in their attempts to nab it. Thus, some have doubts as to whether the nebula can be seen at all. Some have argued that Herschel and others (like his son John who even measured it, suggesting that it extends at least 12 arcminutes north and south of Epsilon Orionis) must have been fooled into believing they had seen something there (even though, coincidentally, it exists). The problem is that the nebula lies within the “glare” of the star, which can be enhanced with the slightest amount of moisture or dew on the telescope objective (a moist breath on the eyepiece), or dust or other pollutants in the atmosphere. I've tried with the 5-inch without success, but that's just me. Others have claimed success. Perhaps it comes down to what Hal Corwin, director of the NGC/IC Project (www.ngcic.org) wrote in November 2006: “I think that we need to get out with big reflectors similar to the Herschels' telescopes and really examine these stars in dark skies. I'd be interested in seeing what the extended star images look like under these conditions, and especially why some stars misled the 19th century guys while most did not.”

Alnitak (800 light-years) is another hot O-type blue supergiant – the brightest O-type star in the sky. To the eye, Alnitak is 20 times more massive, and 10,000 times more luminous, than the Sun; to a bee, who can see in the ultraviolet region of the spectrum, the star's light would appear 100,000 times solar. As University of Illinois astronomer James Kaler touts, “A planet like the Earth would have to be 300 times farther from Alnitak than Earth is from the Sun (8 times Pluto's distance) for life like ours to survive.” And though Alnitak may be about about 6 million years “young” (as opposed to the Sun's 4.6 billion year age), it has already begun to die. Its fate will be to swell into a red giant like Betelgeuse in the shoulder of Orion, and suffer a cataclysmic explosion as a supernova.

Alnitak travels through space with a hot, B-type 5th-magnitude companion 2.6⁰⁰ to the southeast; few seem to agree on the companion's color. William Henry Smyth saw it as “light purple.” William Tyler Olcott said it is “blue.” But in 1836, F. G. Willhelm Struve invented a lovely name for it: olivacea subrubicunda, meaning “slightly reddish olive.” Another “companion,” though most likely not a true physical member, is a 9.5-magnitude star 57⁰⁰ to the northeast.

The region around Alnitak is remarkable as well, containing several dusty clouds of interstellar gas, including the famed “Horsehead Nebula” to the south, and NGC 2024 (Hidden Treasure 34) just 15⁰ to the northeast. If you are under a dark sky, look at Alnitak with keen averted vision (cover the star with the edge of a distant object, like a roof or tree limb, if necessary). Can you see the nebula without optical aid? In binoculars? In 10 ^ 50 binoculars, it's a pale, sepulchral glow (the ghost of Alnitak) that could easily be mistaken for an optical reflection. NGC 2024 is an HII region some 1,300 light-years distant. It is part of one of the closest sites of recent and massive star formation. Energetic photons from young stars strip the surrounding hydrogen atoms of their electrons, causing the gas in the visible nebula to glow. And though you cannot see it, NGC 2024 contains an embedded cluster of stars 300,000 years young.

By the way, the low-power field surrounding Alnitak has several other smaller reflection and emission nebulosities: IC 432, IC 431, NGC 2023, IC 435, and IC 434 (which includes the dark Horsehead Nebula). They are plotted on page 109, but described in detail in my Deep-Sky

Companions: Hidden Treasures book (Cambridge University Press, 2007). Also, what about Sigma Orionis about 50⁰ southwest of Alnitak. It's a stunning multiple star system even in a small telescope, but it's not a part of Collinder 70. In fact, it's a star cluster of its own – the Sigma Orionis cluster, 1,150 light-years distant. It's composed of four members (a tight quartet), which are responsible for illuminating the nebula surrounding the Horsehead. As I write in my Observing the Night Sky with Binoculars (Cambridge University Press, 2008): “Few sights in the night sky excite beginners more than being able to detect this, the most glorious of all nebulae, without optical aid. Its beauty and glory is justly magnified in binoculars and telescopes, which also reveal its little companion nebula, M43, kissing it to the north and the famous Trapezium star cluster at its core.” Enjoy!

S ometime in the mid to late 1970s , the famous visual nova hunter Peter Collins introduced me to NGC 2022. Although I can't recall the exact date, I do recall that winter experience. We were using the 9-inch f/12 Clark refractor at Harvard College Observatory in Cambridge, Massachusetts. At the time, I had been concentrating most of my time to studying the planets, though I had a keen interest in many aspects of visual astronomy, including the deep-sky.

On this night, Peter had come tothe dome excited to show me this planetary nebula, which shone dimly in the nape of Orion's neck. Sometimes seeing planetary nebulae from a city can present a challenge to observers. But NGC 2022 was, to my surprise, quite obvious. Its tiny annulus shined forth like a moist and narrow loop of light.

NGC 2022's true shape is a prolate spheroid (like an American football) surrounded by an almost spherical, fainter shell of matter. Like NGC 1535 (Hidden Treasure 24) in Eridanus, NGC 2022 is a planetary nebula in a rather early evolutionary phase, so it has a high surface brightness. We see two main structures: The most obvious is an inner annulus tilted about 45^{^} to our line of sight toward positional angle 30^{^} in the sky; the other is a fainter, almost spherical shell of matter expanding at a lower rate than the inner ring. The nebula's mean ionized mass (whose emission lines are dominated by neutral hydrogen) equals 0.2 Sun, and its magnitude 14.8 pre-white-dwarf central star has a surface temperature of 100,000 K.

The nebula formed from an asymptotic giant branch star that loses mass at quite a strong rate (10^–5 to 10^–6 solar masses per year) and at a low velocity (5–10 km/sec). When the star begins its fast evolution toward the left of the HR diagram, it ejects a mass of gas of 0.1 to 0.5 Sun with a range of velocity from zero up to 50 km/sec. The outer parts of this gas interact with the former ejected wind. The gas glows as ultraviolet light from the hot central star excites it.

In the early evolutionary phases, the nebula has a high surface brightness and the interaction region is external to the ionized part of the nebula, and this is the stage in which we see NGC 2022. In time, NGC 2022's density will decrease and the radius of its ionized region will extend outward toward the dusty shell surrounding it, causing the nebula to shine with a lower surface brightness.

NGC 2002's inner annulus, the one most obvious in backyard telescopes, measures 22⁰⁰ ^ 17⁰⁰ ; at an approximate distance of 7,600 light-years; the ring's true physical extent, then, is 0.8 ^ 0.6 light-year. The dim outer shell measures about 28⁰⁰ across or 1 light-year. If you look carefully at the HST image at right, you'll see that the inner ring's brightest sections appear at the ansae of the major axis.

HST principle investigator Howard Bond (Space Telescope Science Institute) notes that such bright rims have the expected sheet-like attributes of a bubble-driven snowplow, meaning that as fast wind from the central star expands, it sweeps up the cooler gas like a snowplow.

Planetary nebula expert Sun Kwok (then at the University of Calgary) says that these “‘interacting-winds' have become the standard model of planetary nebulae formation, and have led to a new understanding of the dynamical evolution of planetary nebulae as well as the origin of their different morphologies.” Bond adds that the HST image of NGC 2022 shows that the snowplowed sheets are rather thick and have easily resolved rims with a sharp leading edge.

To find NGC 2022, use the chart on page 110 to locate 3rd-magnitude Lambda (l) Orionis and its two 4th-magnitude attendants – Phi¹ (f¹) and Phi² (f²) Orionis. Center Phi² in your telescope, then switch to the chart on page 113. From

Phi², move 20⁰ south-southeast to 6th-magnitude Star a. Now, head northeast and follow the roughly 50⁰ -long chain of 8th- to 9th-magnitude stars that ends at Star b. Just 10⁰ southeast of Star b you'll find a nice pair of stars: 7.5-magnitude Star c and a 9th-magnitude companion to the southeast. NGC 2022 lies about 10⁰ further to the southeast.

At 33^ in the 5-inch, NGC 2022 is virtually stellar, even with averted vision. It shines as a solitary 12th-magnitude sun in a line of 12th- and 13th-magnitude stars; it blends in with its surroundings well and can easily be passed over. So don't be fooled. Use the chart here to pinpoint its exact location. Once you're certain of its position, see if you can't see it swell just ever so slightly. Remember to use averted vision, and give it time. I really enjoy trying to detect planetaries at low power; it's like trying to coax your eyes to see a white rabbit in the snow. At 60^, the nebula is a very small, pale gray, and highly noticeable disk, nicely condensed; it truly looks like a distant gas-giant planet.

Increasing the magnification to 94^ causes the nebula to stand out boldly against the sky background. The nebula displays a bright disk that remains highly condensed. With concentration, I believe I can start to detect definition – namely a brighter core with fuzzy edges. I find that all powers just tease the eye until I get to about 282^, when the annulus pops clearly into view with averted vision. I see two crescents with sharp inner edges joining to create the ring, thus my nickname for the planetary: the Kissing Crescents Nebula.

Just as HST and other images show, the nebula certainly is brighter around the ansae of the major axis (oriented northeast– southwest). This causes the minor axis, oriented northwest–southeast, to appear dimmer. The southwestern end is particularly brighter than the northeastern end and has a beaded appearance. John Herschel (1792–1871) also noted a beaded texture, describing the nebula as “rather oval, and perhaps a mottled light.” On that note, Admiral William Henry Smyth said

that John's “power of vision [was] beyond what my means afforded.” Smyth employed a 6-inch refractor to observe the nebula, which he found “small and pale, but very distinct.” Perhaps he wasn't using enough magnification.

Smyth did, however, see NGC 2022's disk tinted bluish white – a color also noted by Rev. Thomas W. Webb in his Celestial Objects for Common Telescopes (Dover Publications, Inc., New York, 1962). Planetary nebulae often appear greenish (sometimes bluish) because of an abundance of ionized oxygen [OIII], which radiates in the green part of the visible spectrum. What do you see?

W hen i began taking color photographs of the constellations in the 1970s, a weakly glowing stream of red light, arcing nearly 15^{^} along the eastern side of Orion's Belt and Sword, caught my eye. At first I thought it was caused by a film defect or a light leak in my camera. Later I learned its identity: the emission nebula Sharpless 2-276, more commonly known as Barnard's Loop.

In wide-field photographs, especially in long exposures taken in red light, the Loop looks like the wing of a celestial snow angel made with Orion's right arm and leg. Actually, it's a giant (600⁰ ^ 300⁰ ) swath of ionized gas with a mass of about 100,000 Suns. It was probably produced by the explosion(s) of one or more supernovae some 5 to 6 million years ago – the only such remnant visible to the unaided eye. The nebula's expansion (10 to 25 km/sec) is also being driven by strong stellar winds from the Orion I OB Association, of which the famous Orion Nebula (M42) is a major part; M42 also lies at the heart of the Loop.

In a 1992 Journal of Soviet Astronomy (vol. 36, p. 246A), E. A. Abramenkov and V. V. Krymkin (Radio Astronomy Institute, Ukrainian Academy of Sciences) explain that various opinions have been advanced about the mechanism that excites the emission of Sharpless 2-276. In early papers, the Loop's ionization was explained by either the collision with interstellar gas or cosmic and X-ray bombardment. But modern observations disagree. It's now believed that excitation by hot stars in the OB association causes Sh2-276's thermal emission, whose radiation is scattered by the dust component and emitted intensely by the nebula in the ultraviolet. The nebula's non-thermal component, on the other hand, is typical of those from supernova remnants, which may be due to a compression of the region's interstellar magnetic field induced by the explosion's shock wave.

The Loop's visibility to the unaided eye was, for a long time, a matter of interesting debate, and I will discuss this later. But the Secret Deep object you're after is the brightest telescopic region of the Loop, known as Herschel Region 27.

Despite the Loop's popular name (Barnard's Loop), the legendary visual observer and photographic genius Edward Emerson Barnard (1857–1923) was not the first to discover it. The nebula's history is, in fact, shrouded in “ignorance” – not in a derogatory sense, but in the sense of “not knowing.” The story is one best told backwards, beginning with Barnard.

In his 1995 book, The Immortal Fire Within: The Life and Work of Edward Emerson Barnard (Cambridge University Press), William Sheehan describes how, in October 1894, Barnard used a very small magic lantern lens (1.5 inches in diameter and

• 3.5 inches focus) attached to the Crocker Telescope mounting at Lick Observatory in Southern California to make wide-field exposures that took in nearly the entire constellation of Orion. On those images, he noticed a “great nebula extending in a curved form over the entire body of Orion.”

At the time, Barnard was unaware that Harvard astronomer William Henry Pickering had already imaged it five years earlier from nearby Mount Wilson, using a Voigtlander portrait lens of 2.6 inches aperture and

• 8.6 inches focus.

Barnard acknowledges this in a 1903 Astrophysical Journal article (vol. 17, p. 77) titled “Diffused nebulosities inthe heavens.” He also reveals that on one of his photographs, “Most of the great curved nebula is clearly shown, especially [region 27] described by Herschel.”

“Region 27” is one of several areas of the sky that the great visual astronomer William Herschel listed as being “affected with milky nebulosity.” The table on page 116 gives the region's central position, which lies about 30⁰ south of the midpoint between the 5th-magnitude stars 56 and 51 Orionis. So while the Loop may be rightly called either Pickering's or Barnard's Loop, Herschel definitely was the first human known to spy a segment of it visually. Barnard extolled the wonder of Herschel's region 27 as seen in his photographs, touting it as “really the brightest portion of one of the most extraordinary nebulae in the sky.”

But not all astronomers were convinced. The renowned English photographer Isaac Roberts, for instance, tried to image Herschel's milky nebulosity in region 27 (as well as 51 other nebulous regions described by Herschel) with a 20-inch reflector and 5-inch Cooke Portrait lens. His 90-minute exposures failed to show any trace of these supposed glows in all but four regions – region 27 not being among them.

In his 1903 paper, Barnard immediately addressed this issue: “Dr. Roberts' negative results are so sweeping in character that it is highly important that anything tending to prove the existence of any of these questioned regions of nebulosity should be brought forward at once.”

Barnard went on to argue that Roberts' exposures were too short (imagine that, considering how modern-day astronomers can achieve success with CCD cameras in a matter of seconds), adding, “It is a little unreasonable to suppose that Herschel, who made so few blunders compared with the wonderful and varied work that he accomplished, should be so palpably mistaken in forty-eight out of fifty-two observations of this kind.”

Indeed, Barnard notes that his images show the nebula in region 27, exactly where Herschel had recorded it. In a final verbal thrust, Barnard notes, “Dr. Roberts failed to get any traces of the exterior nebulosities of the Pleiades, which have been shown by four observers with four different instruments not only to exist, but to be not at all difficult objects.”

This debate mirrored many similar arguments in the coming years as to what any given observer could, or could not, see through a telescope, using photography as the sole judge and jury. Some astronomers apparently had so much faith in photography (especially during its infancy) that they were blinded by its imperfections, putting absolute trust in what we now know was an inherently fallible medium – one limited by the technology of the day, especially the insensitivity of old photographic emulsions to faint, diffuse light.

Curiously, Barnard, the greatest visual observer of his day, someone who had discovered the large and dim California Nebula in Perseus, among other awesome visual feats, did not try to detect visually the nebula in Herschel's region 27. Had the great observer sold his soul to the new promise of astrophotography, while retaining a healthy respect for the power of the eye?

In The Immortal Fire Within, Sheehan argues that Barnard largely gave up his visual observations of nebulae after he started making wide-angle photographs with the Willard lens at Lick Observatory in 1889. The lens gave a 20^{^} field of view and had tremendous potential for celestial photography. “I think he realized,” Sheehan explains, “that photography was so much more discerning as a medium for making out these objects. I suppose that the dryplate photography had about the same impact on nebular studies as CCD imaging has had on planetary studies today – to the point where very few observers bother to make visual observations any longer.”

Today, sighting the nebula in Herschel's region 27 is not tremendously difficult – if

you have access to a dark sky, and especially if you employ an ultra-high-contrast filter. Again, I'm asking you to see the brightest part of this Great Curved Nebula (the name that Barnard bestowed upon it), which was discovered visually, not photographically. It runs from a point about 1¼^{^} due east of 5th-magnitude 60 Orionis, near the 9th-magnitude open star cluster NGC 2112, to a point about 1³=4^{^} southwest of 56 Orionis. So its long axis is oriented northwest to southeast, with a midpoint about 30⁰ northwest of open cluster NGC 2112, which is 18⁰ in greatest extent and has about 50 stars 10th-magnitude and fainter.

The nebula's glow is quite substantial, measuring 1½^{^} in length and about 30⁰ wide (the exact dimensions of what you see will vary on the night, your instument's aperture, and the magnification used). The greater the aperture and the lower the power, the more you will see, again, especially with a UHC filter. The dimensions are larger than those of the Veil supernovae remnants in Cygnus and a bit smaller than those of the California Nebula in Perseus, all of which are large visual wonders.

I know of many successful attempts to see the brightest section of the nebula in Herschel's region 27. I was most impressed with its appearance in my Tele Vue 4-inch f/5 Genesis refractor at 23^, the view of which was more enhanced than that through my 5-inch at 33^. That increase of 10^ in the 5-inch was enough to spread the nebula's dim light across a greater area, making it a bit more difficult to detect.

It's a subtle glow that is best seen with a slow and generous sweep – much in the way that Herschel discovered it. As Robert L. Gregory informs us in his 1966 book Eye and Brain: The Psychology of Seeing (McGraw-Hill Book Co., New York, Toronto), part of the function of eye movement is to sweep the image over the receptors, “to signal to the brain the presence of the image.” Herschel, like other observers of his day, employed this technique. “I used every means of ascertaining [these nebulae],” Herschel says, “by motion of the telescope.”

Start your search by sweeping slowly from 60 Orionis toward M78. As you move the tube toward the nebulosity, align your eye so that the incoming light sweeps across the long axis of the eye. As you approach the nebula, the background sky should become a little bit brighter (the presence of the nebula), then fade again as you move away from it. It's a sensation very similar to crossing a highway lit by starlight surrounded by dark grasslands.

In fact, the method you use to see Herschel's nebula through a telescope is very similar to the method experienced observers use to detect the dim zodiacal band with the unaided eye, namely by sweeping the head back and forth across the target region, all the while looking for a dim band of light. You can also try gently tapping the telescope tube; which sets the field in a rocking motion, thus sweeping the nebula back and forth across the retina. (Remember to align your eye with the axis of motion.)

Seeing this large and ghostly veil against stars on the outskirts of the galactic plane is an acquired skill. It takes time and patience, and repeated efforts on dark nights of varying transparencies. Once you see the glow, though, its form becomes more and more apparent with time as your eye–brain system becomes more and more familiar with the view. You're looking for something large and diffuse – a ghostly corridor of elusive vapors some four times as long as, and just as wide as, the apparent diameter of the full Moon.

With the passage of time, I thought I could see actual ribbons of nebulosity. In other words, the view was not that of a large and dim glow but of a frayed fabric. See if you can justify seeing these details in your own eye and mind. I could also detect faint traces of nebulosity in the more northwestern regions of Herschel's region 27, but the number of bright stars in this region is greater, and tracing out the glow is more difficult because of the stellar distractions. It is still substantial, however, in photographs and CCD images.

THE NAKED-EYE LOOP

Although it's not part of the Secret Deep list, seeing the entire Barnard's Loop without optical aid has long been a fun and exciting challenge, testing the visual mettle of even the most skilled observers. Admittedly, sightings of it (or at least parts of it) through UHC and H-beta filters have become commonplace to downright simple; it's one of the advantages of living in a world filled with technological wonders.

Dave Riddle of northern Florida explains how the north part of the Loop is a well-known naked-eye H-beta object. “My previous attempts to follow the nebula southward with an H-beta filter revealed nothing and I had pretty much written off the object as ‘photographic only,'” he says. “When I spotted a large bright glow without the filter in the position of the Southern Loop, I initially was puzzled by what I was seeing and thought it must be one of the weakly illuminated dark nebulae that mottle this area of Orion.” But a followup observation revealed to him that he had indeed sighted the Loop's southern extension. “I could trace the entire nebula that curves westward near 53 Orionis (Kappa),” he says, “and ends just eastward of Rigel.” He also found the “curve” west of Kappa particularly well defined in his Tele Vue Pronto telescope at 16^ with a UHC filter.

I've found the eastern and southern segments of the Loop not that difficult to see without optical aid under dark skies, especially at altitudes 4,000 feet and higher. Beware, however, of Orion's False Loop – a 10^{^} -wide semicircle of light that follows a coincidental curve of nine 4.5- to 5th-magnitude suns. Its northern segment begins at Psi (c) Orionis, which is about 4^{^} north of Delta (d) Orionis (Mintaka), the westernmost star in Orion's Belt. It then arcs northeastward through Omega (o) Orionis, then southeastward through 56 and 60 Orionis, before dipping almost 3½^{^} south to Star a. The far southern extension travels through 49 and Upsilon (u) Orionis just south of the Sword.

With averted vision, these stars appear as a fuzzy beaded necklace owing to the “etcetera principle”: Under low light level situations such as stargazing, our eye–brain system not only likes to play “connect the dots” (in an attempt to create familiar patterns), but also fill in the blanks; in this case, causing us to see a fuzzy loop.

To see the true nebulosity, try tackling it bit by bit. Start with Herschel's region 27 (about 1^{^} south of 56 Orionis) and its south-southeastern extension (which ends about ½^{^} west of Star a). If you have trouble seeing it, try this averted vision trick: Look at Omega Orionis but focus your attention on the region of sky between 56 and 51 Orionis. You can also try directing your attention at the point halfway between Psi and 56 Orionis, or, better yet, alternate between the two views. If you suspect something, sweep your direct gaze from 51 Orionis to 2nd-magnitude Zeta (z) Orionis (Alnitak), while using your averted vision to seek out the region of the Loop extending toward Star a. Now focus on a point above Orion's Sword but concentrate on the region between Star a and 55 Orionis.

The Loop's most difficult region in the south lies midway between 2nd-magnitude Kappa (k) Orionis (Saiph) and 0-magnitude Beta (b) Orionis (Rigel). Seeing this thin wisp of light requires not only patience and rhythmic breathing, but also perhaps the advantage of altitude; it also helps to extend your fingers to block these two bright stars.

As Riddle said, the northern segment of the arc is an H-beta object. I have never convinced myself that I've seen the glow between Omega and Psi Orionis without a filter. The biggest problem is that the nebula unfortunately follows a string of dim suns between them, and it's hard to tell if the etcetera principle is not at work.

By the way, amateurs have spied sections of the western part of the supernova remnant, more formerly known as the Eridanus Bubble – a 25^{^} area of interlocking arcs of H-alpha-emitting filaments, driven by stellar winds and supernovae. The brightest segment is NGC 1909. Once believed to be a nonexistent object, it is is now known to be coincident with IC 2118, the Witch Head Nebula in Eridanus. Riddle has spied it through apertures as small as 70-mm.

ic 2149 is a peculiar little gem in northeastern Auriga, near 2nd-magnitude Beta (b) Aurigae (Menkalinan) – the shoulder of the Rein-holder. This important planetary nebula was discovered in 1906 by Williamina Paton Fleming (1857–1911) – one of Harvard College Observatory's best-known woman astronomers in the world. Fleming permanently joined the observatory staff in 1881 and observatory director Edward C. Pickering soon entrusted her (and other stellar women assistants) with the monumental and fatiguing task of examining, indexing, and caring for the photographic plates in Harvard's growing collection.

While visually scanning the plates, Fleming and her coworkers not only measured the positions of thousands of stars (and compared their results against those in known catalogues), but also searched eagerly for new objects by means of their spectra. “Many departments of astronomy have been revolutionized by the application of photographic methods,” touts Pickering in a 1908 Annals of the Harvard College Observatory, “Among them may be included the discovery of nebulae by means of their spectra.”

Indeed, Fleming's discovery of IC 2149 came as she inspected plates taken with Harvard College Observatory's 8-inch f/5.5 Bache refractor, which was equipped with an objective prism to record spectra. It was during one of these scans that she noted a star in Auriga whose spectrum displayed peculiar bright lines; this object – one of 43 objects she ultimately added to the Index Catalogue – she listed as a “gaseous nebula,” a phrase commonly used back then to describe planetary nebulae.

At the time of Fleming's discovery, the Bache refractor was no longer at Cambridge, but at Harvard's southern station in Arequipa, Peru. Interestingly, had not circumstances changed there by 1898, the discovery of IC 2149 (and many others) might not have gone to Fleming. In 1897, the hunt for variable stars and other new objects had become increasingly competitive.

As Bessie Zaban Jones and Lyle Gifford Boyd explain in their 1971 book, The Harvard College Observatory: The First Four Directorships, 1839–1919 (Belknap Press, Cambridge, MA), Harvard astronomer Solon Bailey, who took charge of the Arequipa station in 1893, began to encourage his Peruvian assistants to scan the photographic plates before boxing and shipping them off to Cambridge. If they found a new variable or other interesting object, Bailey told them to mark it.

This practice displeased Fleming, who felt she was being deprived not only of the joy of discovery but of original discovery credit. In a letter to Bailey, Pickering raised Fleming's concern, noting that her work was now being duplicated by Bailey's assistants. “She feels that in these cases the credit goes to the Peruvian observers,” Pickering said, “while a large amount of work falls upon her.” But Bailey defended the practice, saying that the person who took the plate (and inspected the result) shouldn't be forbidden to note the appearance of new objects.

Pickering was sympathetic: “Personally, I think that the ability to make first class plates is greater than that required in the mere picking up of new objects by the assistants there. . . But the latter has been publicly recognized and the former seldom or never, it is perhaps not strange that an ambitious assistant should desire to try also the latter . . . Mrs Fleming is not the only one who has felt vexed at times.”

The matter seemed to end when Bailey turned his post over to William F. Clymer in December 1897 and headed back to America; though in a letter to Clymer, Pickering made a preemptive strike: “Evidently it is for the mutual interest to avoid duplication [in the efforts of all] and there surely should be some way by which justice should be done to all.” For instance, Pickering suggested to recognize in print “the assistant by whom each photograph is taken.” If anyone had a problem with this, Pickering said, they could take it up with him.

In 1899 Pickering made Fleming Curator of Astronomical Photographs – the first such corporation appointment of a woman at Harvard. And in 1906, the year she discovered IC 2149, the Royal Astronomical Society elected her as an honorary member.

IC 2149 has long been an enigma among planetary nebulae, eluding clear classification until 2002. In optical images, the compact (8.5⁰⁰ ) nebula displays a bright elongated central structure surrounded by a faint envelope. It is dominated, however, by the light of its 11.3-magnitude central star. Of spectral type O7.5, this low-mass star (~0.5 Sun) has an effective temperature of about 30,000 kelvin and a stellar wind (~1,000 km/sec) indicating a massloss rate of around 10^–8 solar masses per year. The metal-poor central star (whose progenitor was about the mass of our Sun) appears to be slowly evolving and is only about 7,000 years young; this would also explain the small, highly ionized nebula around it.

Hubble Space Telescope images, as well as Earth-based imaging and spectra, have revealed important structures within the low-mass nebula (~0.03 Sun). As Mexican astronomer Roberto Va´zquez (Instituto de Astronom´ıa, UNAM, Ensenada) and his

colleagues describe in a 2002 Astronomical Journal (vol. 576, pp. 860–869), the nebula's bright inner ellipse is an inhomogeneous ring seen almost edge-on. Assuming that the ring is circular, it would be inclined 86^{^} with respect to the line of sight (with the southeast half of the ring angled toward us). At an assumed distance of ~3,600 light-years, the ring's width spans some 0.2 light-year and is expanding at 24 km/sec.

Earth-based observations indicate that an elliptical (oblate ellipsoidal) shell surrounds the ring. In addition, arclike structures at the ring's ansae suggest the possible presence of faint bipolar lobes. Thus, the authors conclude, IC 2149 can be suitably classified as a bipolar planetary nebula (diabolo or hourglass type) with the main (bipolar) axis at position angle -23^{^} .

The presence of an ellipsoidal shell suggests that the nebula may still be in the process of forming and that complete bipolar lobes could develop in the future.

us different stages in the final evolution of low-mass central stars, with NGC 4361 being the more evolved.

To find this tiny wonder, simply use the chart on page 123 to locate Beta (b) Aurigae and 4th-magnitude Pi (p) Aurigae, just 1^{^} to the north. Center Pi in your telescope at low power and use the chart on page 126 to find IC 2149 only about 40⁰ to the westnorthwest. Pi marks the eastern end of a roughly 25⁰ arc of three stars; you want to center the westernmost star (labeled a). Now look about 12⁰ further west for a dim pair of stars (b), whose components shine between magnitudes 10 and 11. About 6⁰ northwest is a solitary 10th-magnitude star (c). IC 2149 is almost 10⁰ to the northeast, about midway between Star c and another 10th-magnitude star (d ).

At low power, you probably won't see the nebula hugging the star . . . just the star. So center that star, and get ready to use high powers. Once you're sure you've located the star, though, try to see if you

can't make the star “swell” with averted vision. I convinced myself I could at 33^. Again, since the nebula is so small (8.5⁰⁰ ), you'll want to crank up the power. Use as much as you, and the night, can handle. The nebula is of high surface brightness, so go to the highest extreme. I found the view of the nebula (just as a glow) “comfortable” at magnifications between 165^ and 180^. Double those powers and you may start to see tiny structures.

By alternating between averted and direct vision, the nebula expands and contracts (albeit minutely), respectively. An OIII filter creates a bizarre effect.

As you peer at this seemingly insignificant 11th-magnitude star surrounded by an annoyingly small and trivial bit of fuzz (perhaps even wondering why I would include such a visually lame object), consider this: In a 2008 Monthly Notices of the Royal Astronomical Society (vol. 386, p. 155), Klaus-Peter Schro¨der and Robert C. Smith

compare the current appearance of IC 2149 with that of the expected final stage in the life of our Sun.

While our Sun will become a 0.3 solar mass red giant 7.6 billion years from now, the authors say, its luminosity will come short of driving a final, dust-driven superwind. No regular solar planetary nebula will form, they argue. Instead, a last thermal pulse may produce a circumstellar shell similar to, but rather smaller than, that of IC 2149. At that point, the Earth will be engulfed by the Sun's cool giant photosphere!

Does the thought of that event annoy you? How lame and insignificant do you think that moment in our Sun's life will appear to future backyard astronomers – those living on an Earth-like planet orbiting a type G2 star some 3,600 light-years distant? Would they think it a waste of time to search for such a visual trifle? In the grand scheme of things, just how significant are we? The answer may lie in your perception of IC 2149.

m 42, the great nebula in orion, is the most stunning nebula visible from mid-Northern latitudes and the most popular Messier attraction. Peering into this vast and brilliant cloudscape of dust and gas, a fanciful tapestry of delicate loops and folds draped across 20 light-years of space, is a favorite pastime of many amateur astronomers on cold winter nights. But what is sometimes overlooked is that M42 lies at the heart of the much larger Orion–Monoceros complex of molecular clouds – one of the most important and best studied regions of star formation. Our next two Secret Deep targets, NGC 2149 and NGC 2170 in Mono-ceros, are tiny parts of that enormous structure, but have special features that may share in M42's history.

William Herschel discovered NGC 2170 in 1784, but equally bright (and I would argue more obvious) NGC 2149 somehow escapedhisgazeandthatofhisson John. The renowned French astronomer E^´ douard Jean-Marie Stephan (1837– 1923) first detected NGC 2149 through the 31.5-inch silvered glass reflector at Marseille Observatory, where he was director. The discovery was part of a program to seek out new nebulae, which began in vigor in 1869 and lasted until 1884 (see Secret Deep 102 (NGC 7048) for more information about Stephan's search). NGC 2149 was one of 420 nebulae he catalogued and sent to John Louis Emile Dreyer, who was collecting data for the 1888 New General Catalogue (NGC).

Before we look more closely at NGC 2149 and NGC 2170, it's important to “break down” the Orion–Monoceros complex into its smaller components. The Orion–Monoceros complex lies 15^{^} below the Galactic plane toward the outer Galaxy. It serves as an excellent laboratory for studying the interaction between massive stars and the interstellar medium. Over the course of the last 12 million years the molecular clouds in the region have been shaped, compressed, and disrupted by the powerful ionizing radiation, stellar winds, and supernova explosions of the young massive stars in the Orion OB association.

The complex contains three giant (100,000 solar masses) molecular clouds (Orion A, Orion B, and Mon R2 (to which NGC 2170 belongs)), two long filaments, which extend approximately 10^{^} from the cloud complex to the Galactic plane, and numerous smaller molecular clouds (of which NGC 2149 is an example).

In a 2009 Astrophysical Journal (vol. 694, p. 1423), Hsu-Tai Lee and W. P. Chen (National Central University, Taiwan) say that most of the molecular clouds in the complex are located on the border of the Orion–Eridanus Superbubble. This large cavity in the interstellar medium was created by at least six or seven supernova explosions that have occurred in the past 5 to 10 million years, the combined energy of which has blown the bubble out to a diameter of about 1,000 light-years. The Superbubble is still expanding at about 20 km/sec (13 miles per second), comparable to the speed of an expanding shock wave from a powerful nuclear blast.

The supernovae responsible belong to the same OB association – in this case the Orion OB1 association, which includes young, hot stars in several famous objects: M42, M43, M78, NGC 2024 (Hidden Treasure 34), and Barnard's Loop, to name a few. The researchers note that star formation in the Orion OB1 association progresses from the oldest subgroup, Orion OB1a (the area around the Belt (see Secret Deep 24)), to 1b (which lies northwest of the Belt stars), to 1c (the region containing Orion's Sword), and 1d (a special class that separates out M42 and M43; the youngest stars of the Orion OB1 Association).

But the Superbubble, they say, also compresses and initiates starbirth in clouds such as NGC 2149 in the deep southwestern recesses of Monoceros, which is located more than 330 light-years away from the center of the Superbubble. “A superbubble appears to have potentially a long-range influence in triggering nextgeneration star formation in an OB association,” they say, adding that they traced its effects out to 650 light-years from its core.

Reflection nebula NGC 2149 itself appears to be a giant expanding ring between the high longitude end of the Orion A Cloud and the Mon R2 Cloud. In most projections, these clouds appear to be unconnected. However, in a 2008 Astronomy & Astrophysics, B. A. Wilson (University of Bristol), Thomas M. Dame (Harvard-Smithsonian Center for Astrophysics), and colleagues say that their three-dimensional display (with velocity as the third dimension) indicates that the clouds in this region may be connected to form a ring. If NGC 2149's distance is 1,300 light-years, they note, the diameter of the ring is about 260 light-years, which corresponds to an expansion age of about 9 million years and may be the result of a supernova.

NGC 2170 on the other hand is part of the Mon R2 giant molecular cloud. Although this region is about 1,000 light-years more distant than the Orion OB1 Association, it's of similar size and mass. It's also located at the same distance below the Galactic plane and has a similar velocity gradient. “[W ]hen confronted by the numerous similarities between Orion A and Mon R2,” the researchers conclude, “it is difficult to avoid speculating that these clouds, and by extension all the clouds in the region, share a common origin.”

Indeed Carl Heiles (University of California, Berkeley) proposed that the formation of Orion–Monoceros was associated with the expansion of the Vela Supershell, which may have originated from the open cluster Collinder 121 in Canis Major and at a distance of about 1,800 light-years. The Vela Supershell encloses an enormous irregular bubble in the region where it has blown out of the Galactic plane. John Bally (University of Colorado) proposed that the Vela Supershell first collided with a fossil remnant of the Lindblad Ring – a 30- to 60-million-year-old fossil supershell driven into the local interstellar medium by a massive OB association whose remnants are recognized as the Cas–Tau group – which then may have played a role in triggering the formation of the proto Orion–Monoceros complex.

NGC 2170 is the brightest and westernmost of several reflection and emission nebulae in the Mon R2 region about 3½^{^} northeast of NGC 2149. In photographs, the NGC 2170 region is a visual playground – a 1^{^} -long ghostly corridor (oriented east-northeast–west-southwest) lined with cobweb-like blue (reflection) and red (emission) glows and dark dusty threads illuminated by burning blue suns. The photo-ionizing energy and rushing winds from massive stars formed in this stellar nursery are believed to have

scoured and shaped the surrounding natal clouds, creating a tapestry of light and color that, though on a smaller scale, rivals the beauty of Orion Nebula.

To find these intriguing wonders, begin with NGC 2149. Use the chart on page 128 to locate 2nd-magnitude Kappa (k) Orionis (Saiph), then the roughly 5th-magnitude sun 3 Monocerotis about 3½^{^} to the eastsoutheast. Now use the chart on this page to locate 6th-magnitude Star a about 1^{^} east-northeast. NGC 2149 is about 40⁰ northwest of Star a.

At 33^ in the 5-inch, NGC 2149 is a faint fan of light trapped between two roughly 11th-magnitude suns, oriented northnorthwest–south-southeast and separated by about 5⁰ ; the nebula is a bit closer to the northern star in the pair and a tad east of the line joining them. The field is quite rich, making it a pleasing view. I find the nebula swells nicely with averted vision. At this low power, the nebula appears larger than it should owing to the richness of the field.

The view at 60^ is quite different, revealing a dim central star (perhaps magnitude 12.5) in a 4⁰ -wide glow. The star is surrounded by a patchy inner shell that's brightest to the east. This eastern side also has a fainter shell that creates the illusion of fanning; I say illusion, because, as you can see in Mario Motta's revealing photograph on page 128, the nebula sports a dark cloud on its western side, making it appear lopsided. At 94^, a dimmer sun (perhaps 13th-magnitude) lies immediately to the southwest of the central star. The eastern side of the nebula is quite pronounced and seems spiked at the northern and southern ends. The western side appears to have an arc of light surrounding the dark void. So, even though I could not distinctly see the dark cloud, it is nonetheless apparent in my drawing. When I returned to 33^ and used averted vision, I suspected an even wider, fainter glow surrounding the main nebula. See what you think.

To find NGC 2170, look about 4½^{^} to the northeast for 4.5-magnitude Gamma (g) Monocerotis, then use the chart on page 132 to find 5th-magnitude Star a nearly 50⁰ to the west-southwest, which is paired with 6th-magnitude Star b, about

20⁰ to the southwest. From Star b,movea little more than 30⁰ west to 6.5-magnitude Star c. NGC 2170 lies a little more than 30⁰ to the northwest, about 12⁰ southeast of 6.5-magnitude Star d.

At 33^, NGC 2170 appears as a roughly 9th-magnitude double star, oriented northeast–southwest, with the 2⁰ -wide circular nebulosity centered on the northeastern member. With averted vision, the nebula fades away from that star and touches (tickles) the southwestern companion, so it appears slightly elongated in that direction. At 94^, I can see a much dimmer star to the north, and wings of nebulosity stretching to the northwest and southeast. Otherwise, this nebula is one of the simplest in the heavens, and it's simply beautiful just for that.

If you feel adventurous you could look for NGC 2182, a dim reflection nebula 30⁰ to the east-northeast; and the fainter pair of nebulae, NGC 2183 and NGC 2185. Interestingly, while Herschel discovered NGC 2182 and NGC 2185; Heinrich d'Arrest found NGC 2183, which is only about 5⁰ to its west.

By the way, at a 1999 American Astronomical Society meeting in Chicago, Heiles, who discovered the Orion– Eridanus Superbubble in 1970, and a University of Wisconsin team headed by Ron Reynolds, explained how they combined infrared, optical, and X-ray observations to create the most complete picture to date of the Superbubble, which shows both its near and far walls. In one area, however, they could see no rear wall, which, in X-rays, shows gas leaking out. “This hole is like a champagne bottle just uncorked,” Heiles revealed in a University of California, Berkeley, press release, “The high pressure gas inside pops out the hole with explosive force.”

ngc 2281 is a very pretty and bright open star cluster in the obscure eastern reaches of Auriga the Charioteer. The late deep-sky veteran Walter Scott Houston of Connecticut noted that it is seldom observed, perhaps because of its “sideline” nature – it lies well outside the beautiful Pentagram of Auriga, which contains three stunning Messier open clusters (M36, M37, and M38). The Victorian poet Alfred, Lord Tennyson saw the Pentagram as a funerary wreath. In his dusky 1855 poem Maud, in which a man hopelessly tries to contact the dead, Tennyson likens Auriga at winter's end to a “glorious crown” hanging “Over Orion's grave low down in the west.”

But NGC 2281, in fact, resides in one of the seven lashes of the Charioteer – a curious but ignored part of the constellation consisting of ten 5th-magnitude stars (Psi¹ (c¹) through Psi¹⁰ (c¹⁰)); I call this region Psi-clone Alley. It lies about 3/4^{^} southwest of Psi⁷. It also lies beneath the southwest quadrant of the now obsolete constellation Telescopium Herschelii (Herschel's Telescope), which celestial cartographer Johann Bode created to honor the the telescope William Herschel had used to discover the planet Uranus, as depicted in Bode's 1801 Uranographia atlas. As Ian Ridpath shares in his wonderful 1989 book Star Tales, “Bode, having bought telescopes from Herschel, knew what they looked like and he realistically depicted the 7-ft telescope with which Herschel actually made the discovery of Uranus.”

Under a dark sky, I could spy NGC 2281 in 7 ^ 50 binoculars, appearing as a large diffuse glow nestled between two 7th- and 8th-magnitude stars. Can you see it with the unaided eyes? What's more, both of these stars have dramatic golden hues, adding to the glory of the scene. Here is a dazzling pendant of suns hanging from an imaginary necklace anchored by two golden clasps. Trumpler listed it as a type I3m, meaning that it's a detached and moderately rich cluster with a strong concentration of bright and faint suns 8th-magnitude and fainter. In a 2004 Astronomische Nachrichten, Ukranian astronomer N. V. Kharchenko (Main Astronomical Observatory) lists the distance to NGC 2281 as 1,800 light-years; if we accept that value, NGC 2281 spans only 13 light-years of space. And because this interarm cluster lies on the fringe of the visible Milky Way, its stars are reddened by only 0.1 magnitude.

NGC 2281 is some 300 million years old, making it younger than the ~625 millionyear-old Hyades (Caldwell 41) and older than the ~100 million-year-young Pleiades (M45). At a declination of þ41^{^} it is well placed for observations in the Northern Hemisphere, culminating after sunset in late winter.

In a 1975 Publications of the Astronomical Society of the Pacific, Masanori Yoshizawa (University of Kyoto, Japan) says that his photometric study of the cluster shows it to have a rather short main sequence, owing to the fact that 25 percent or more of its bright members are binary systems. The binaries in NGC 2281 are of both low and high mass and concentrate toward the cluster center more intensely than single stars. It is believed that binary stars formed at the same time as single stars in open clusters.

As with other clusters, the heaviest single stars and binary systems tend to concentrate at the core while the lighter stars tend to populate the outer periphery. Over time, stellar encounters eject individual stars, reducing their mass in the process and causing the cluster to contract. The more tightly bound binaries become at the core, the more energy they add to impart to other stars, inhibiting further contraction and offering stability to the cluster system.

To find this neglected treasure, use the chart on page 133 to locate 2nd-magnitude Beta (b) Aurigae and 2.6-magnitude Theta (y) Aurigae. NGC 2281 forms a nearequilateral triangle with these stars to the east. You'll find the cluster about 45⁰ southsouthwest of 5th-magnitude Psi⁷ (c⁷) Aur, which is part of a pretty, 3^{^} -wide, Y-shaped asterism of similarly bright stars – the others being Psi² (c²), Psi⁴ (c⁴), and Psi⁵ (c⁵) Aurigae. Confirm these stars in your binoculars, then center Psi⁷ (the

southernmost one) in your telescope at low power. Again, NGC 2281 should be easily identified some 45⁰ to the southsouthwest.

At 33^ in the 4-inch, NGC 2281 is a beautiful cluster with some three dozen irregularly bright suns radiating out from a tight, diamond-shaped asterism at the cluster's core; a tail of four stars extends to the east, before making a sharp jog to the north. These are some of the brightest stars in the cluster and together they look like a diamond-headed snake. The cluster also has loose arms extending to the south, east (beyond the snake), and north; the northern arm loops broadly to the west and south.

Overall, the cluster looks like a tortured stellar system, one that's been “stretched on the rack,” in all four directions, creating gumby-like arms in the process. The surrounding Milky Way makes it difficult to judge the cluster's true extent, but don't let that stop your wandering eye from enjoying the view. NGC 2281 has about 120 members 8th-magnitude and fainter, with many of the fainter stars hovering around 13th magnitude. Again, add the golden companions nearby, and the overall view is quite stunning and bright.

The cluster is best admired at 60^ and 94^, which show about 50-odd suns at a casual glance. At 60^, the stars of the central diamond stand out boldly, since they are all of near-equal magnitude. Look especially at the southeastern and northeastern members, since they're close doubles; in photographs, the southeastern star is a triple with companions getting progressively fainter to the westnorthwest. The diamond is surrounded by a loose and coarse gathering of mixed suns that form various geometrical patterns. The rest is up to you to decipher, since imagination is a personal matter of opinion. The Albuquerque Astronomical Society list refers to this cluster as the Broken Heart.

ngc 2298 is a surprisingly condensed and obvious globular cluster tucked into the far northwestern reaches of Puppis, near the Canis Major and Columba borders. It's easily located 3^{^} south of 3rd-magnitude Kappa (k) Canis Majoris, the star marking a bend in the Greater Dog's most southerly leg. With a declination of ^36^{^} , it is only about 1^{^} further south than open cluster M7 in Scorpius, the most southerly Messier object. Observers at mid-northern latitudes can best spy it at culmination, when it sits about 10^{^} above the southern horizon.

Of course, dark skies and a southern horizon with few or no obstructions will help immensely. At more southerly latitudes across the continental United States and beyond, NGC 2298 is a gleaming little treasure among the rich star fields along the western fringes of the Milky Way, where there is little interference with dust. So our view of it is relatively clean and clear.

James Dunlop (1793–1848) discovered the little gem while surveying the southern night sky from Australia with a 9-inch f/12 reflector. He listed it as the 578th object in his 1828 A Catalogue of Nebulae and Clusters of Stars in the Southern Hemisphere, Observed at Paramatta in New South Wales. Of it he wrote: “A pretty bright round nebula, 3⁰ or 4⁰ diameter, moderately condensed to the centre. This is resolvable into stars.”

John Herschel observed the cluster four times during his survey of the southern skies from the Cape of Good Hope, which began in 1834. A summary of these observations reveals NGC 2298 to be a small globular cluster (2.5⁰ ), irregularly round and gradually brighter toward the middle. He resolved it into stars of 14th- to 16th-magnitude “with stragglers and some large stars near.”

Today's astronomers recognize the importance of this tiny cluster. Of the 150-odd Galactic globular clusters known, NGC 2298 is one of the smallest, measuring only about 50 light-years across – about one-third the true linear extent of M13 in Hercules, and one-fourth the size of 47 Tucanae. The cluster resides in the inner halo at a distance of 51,000 light-years from the Galactic center. Although NGC 2298 lies almost twice as far from the Galactic center as other, better studied clusters, astronomers have obtained high-precision photometry of NGC 2298's upper main sequence. They have also used the Hubble Space Telescope to perform accurate photometry of cluster members deep in the cluster's core.

Studies of globular clusters are one of the main tools for understanding whether our Galaxy formed by merging with small satellite galaxies or after a rapid halo collapse. While the two models may not be exclusive, recent support for the mergers came from the discovery of very young clusters in the Milky Way's halo (which appear to have formed differently from the vast majority of Milky Way globulars), and also by the discovery in 1994 of the Sagittarius dwarf galaxy, which the Milky Way is swallowing. In fact, globular cluster M54 may be the Sagittarius dwarf's nucleus. Thus, not only may our Galaxy grow by cannibalizing smaller systems, but its globular cluster system may be, in part, composed of extragalactic immigrants from neighboring dwarf galaxies and proto-galactic fragments that our Milky Way accreted.

In 2003, an international team of astronomers used Two Micron All Sky Survey (2MASS) infrared data to find the dismembered corpse of yet another previously unknown galaxy being cannibalized by our Milky Way. Known as the Canis Major dwarf, its nucleus is surrounded by several Milky Way globular clusters, including NGC 2298, which belongs to the dwarf 's globular cluster system. The other associated globulars may be M79 in Lepus, NGC 1851 (Caldwell 73) in Columba, and NGC 2808 in Carina.

The researchers also found long streams of stars that have apparently been gravitationally ripped away from the dwarf's main dismembered corpse during the merger. Computer simulations show that the Milky Way has been taking stars from the Canis Major dwarf and adding them to its own disk, and will continue to do so. In a 2MASS press release, Michele Bellazzini (Bologna Observatory) says, “This small galaxy is unlikely to hold together much longer. It is being pushed and pulled by the colossal gravity of our Milky Way, which has been progressively stealing its stars and pulling it apart.” The illustration on page 140 shows the location of the newly discovered galaxy and its associated tidal streams in relation to our Milky Way Galaxy.

In a 2004 Astronomical Journal (vol. 127, pp. 3394–3398), Australian astronomer Duncan A. Forbes (Swinburne University, Hawthorn, Victoria) and his colleagues

summarize their study of the Canis Major dwarf 's globular cluster system, including NGC 2298. The 12.9-billion-year-old cluster is moderately metal poor, and its stars contain, on average, about 1/70 as much iron (per unit hydrogen) as does our Sun. The fact that NGC 2298 and the other Canis Major dwarf clusters are all metal poor argues against the belief that the Canis Major dwarf is a major building block of the Milky Way's thick disk – a flattened, highly rotating system in the Galactic plane with a relatively high metal-licity. Instead, they are more typical of halo globular clusters.

Forbes et al. conclude that even when satellite accretions add globular clusters to the Milky Way's system, such additions are unlikely to contribute significantly to a thick disk or the bulge population of globular clusters. Based on studies of halo stars, it appears that only about three to seven dwarf accretions may have occurred over the Milky Way's lifetime, contributing only about 10 percent to the mass of its halo. If the Milky Way's young, metal-poor globular clusters have been accreted from treasure, use the chart on page 137 to locate Alpha (a) Canis Majoris (Sirius), then 1.5-magnitude Epsilon (ε) Canis Majoris (Adhara) in the lower leg of Canis Major, the Great Dog. Now look for 3rd-magnitude Kappa (k) Canis Majoris about 4^{^} to the south. Kappa forms the northwestern apex of a 2^{^} -wide triangle with two 5.5-magnitude suns, the eastern one of which is t Puppis. You want to center the western star in that triangle (a) in your telescope then switch to the chart on page 141. From Star a, move 40⁰ southwest to 7th-magnitude Star b. Then drop 50⁰ south to 8th-magnitude Star c. NGC 2298 is only about 12⁰ south-southeast of Star c and 35⁰ northwest of 6th-magnitude Star d.

In the 5-inch at 33^, NGC 2298 is a moderately condensed glow measuring a few arcminutes across. It lies in a hook of stars, which is part of a rich and pretty Milky Way field. The cluster just seems to burn steadily like a trusted beam of light. I could see it without difficulty with direct vision and notice structure with averted vision, namely sparkling clumps in the outer halo. At 60^, the clumps in the tight

outer halo appear more prevalent, while the core itself breaks up into fine mottled patches.

At 94^, individual stars pop in and out of view in the halo, which looks irregularly round with long wispy extensions flowing to the northwest, west, and southwest; some shorter wisps also extend outward from the cluster's eastern side. Increasing the power to 165^, then to 330^, reveals two layers of starlight: a scrim of about a half-dozen obvious suns, mostly flowing to the southwest and northwest, and a fainter orb of dim suns at the threshold of visibility.

Certainly observers with larger apertures should be able to resolve this cluster well; its brightest stars shine around 13th magnitude, with a horizontal branch magnitude of around 16th magnitude.

By the way, since the nucleus of the Canis Major dwarf lies only about 25,000 light-years away from the Solar System and 42,000 light-years from the Milky Way's center – or about three-quarters of the distance to the Sagittarius dwarf and a quarter of the distance to the Large Magellanic Cloud – it is now recognized as the closest known galaxy to the Milky Way. So add that fact to your astronomical trivia. And remember, when you're spying NGC 2298, you're viewing part of an extragalactic system being swallowed by the Milky Way. If you can resolve the stars of NGC 2298 through your telescope, you're resolving stars that belong to another galaxy!

Most veteran observers are well aware of the most observed cometary nebula in the heavens: NGC 2261 (Caldwell 46), more popularly known as Hubble's Variable Nebula, or what I call Herschel's Forgotten Fan, in Monoceros. But what some are unaware of is that Monoceros has another cometary nebula: our target, NGC 2316 (Parsamyan 18). What's more, it's only 1^{^} northwest of M50, the brightest binocular open cluster in Monoceros just 7^{^} north of 4th-magnitude Gamma (g) Canis Majoris.

Although William Herschel discovered it in 1785, the Third Earl of Rosse (1800– 1867) in Ireland rediscovered it in 1851, thinking, however, that it was a new object. John Louis Emil Dreyer (1852–1926) gave it a separate NGC number (2317) and positioned it about 1⁰ west of Herschel's nebula, noting that it makes “a close double nebula with [NGC 2316]).” It's commonly believed, however, that Rosse's object is only a part of Herschel's NGC 2316.

The term “cometary nebula” is essentially an “historic relic” that describes the photographic and visual appearance of a distinctive group of nebulae: small clouds of dust and gas that resemble a comet with a stubby tail. Today, cometary nebulae are those little nebulae that not only look like a comet but are connected with a star of the T Tauri or related variable variety – very young, lightweight stars, less than 10 million years old and under three solar masses that are still embedded in their natal clouds and undergoing gravitational contraction; they represent an intermediate stage between protostars and low-mass main-sequence stars like our Sun. Some cometary nebulae display variability over time and appear bright at long-infrared wavelengths.

In 1965 Elma S. Parsamyan examined Palomar Sky Survey prints in a quest to discover new or little-known cometary nebulae. Of the 23 objects she identified, NGC 2316 was the 18th on her list. In a study of 19 of these, Martin Cohen (University of California, Berkeley) found only five objects that displayed significant long-wavelength radiation of at least 10 micrometers, with NGC 2316 being the reddest. Consequently, in a 1974 Publication of the Astronomical Society of the Pacific (vol. 86, p. 813), Cohen redefined this group of objects, placing them into four morphological subsets: (1) arcuate structures, like the incomplete ring near T Tauri; (2) conical or fan nebulae, like NGC 2261; (3) nebulous appendages, like commas (Z Canis Majoris); and (4) bicones or hourglasses.

Cohen also noted that the nebulae are almost invariably associated with stars or starlike condensations, which lie in a position of geometrical significance, such as in the waist of an hourglass, or near the apex of a fan. The nebulae also have small apparent diameters, usually 2⁰ or less, and the definition of the visible structures is crisp and well-defined, very rarely being associated with larger swaths of surrounding nebulosity.

NGC 2316, he found, is a bright conical nebula very reminiscent of NGC 2261 near R Monocerotis. The nebulosity contains two small (~10⁰⁰ ) condensations, the brighter one being located near the apex of the cone; this condensation has a very high infrared luminosity – between 11.3 and 18 micrometers, making it the reddest observed of any object then known to Cohen, with a color temperature close to 100 K. The nebula also envelops a small cluster of faint red stars.

In a 2008 Astronomical Journal (vol. 136, pp. 602–613) T. Velusamy ( Jet Propulsion Laboratory) and William Langer (JPL/ Caltech) describe how they used infrared data from NASA's Spitzer Space Telescope to resolve that young star cluster, which spans 4 light-years across. They found more than 200 cluster members with an age of about 2.5 million years. They identified a B3 zero-age main-sequence star as the main power source; that star is still embedded in a nearly spherical HII region (dimming it by about 4.5 magnitudes), which is being shaped and chemically altered by ultraviolet radiation emitted by this young star.

To find this little nebula, use the chart on page 142 to locate brilliant Sirius, the Alpha star of Canis Major, then look 5^{^} east-northeast for Gamma (g) Canis Majoris. The 6th-magnitude open cluster M50 will be 7^{^} north of Gamma. Center that cluster in your telescope at low power, then switch to the chart on this page. From M30 move only 35⁰ west to 6th-magnitude Star a. About 10⁰ west of it, you'll see

a roughly 15⁰ -long line of three 8th- to 9th-magnitude stars (b). NGC 2316 is just a little more than 20⁰ due north of the northernmost star in that line, about 10⁰ southsoutheast of 9th-magnitude Star c.

I spied the nebula at 33 ^ in the 5-inch with averted vision. It lies within 2⁰ north of a little arc of three roughly 12th-magnitude stars. At this power, the arc of stars and the nebula seem to glow as one object. It takes magnification to separate them well. At all powers up to 94^, the nebula appears much the same: a highly condensed, irregularly round glow with a fainter fan of nebulosity stretching toward the arc of stars. In my scope, though, it's hard to make any definition out in the fan. Those using larger telescope should look for a delicate “bubble” of glowing gas surrounding, and centered on, the middle star in the arc – the one closest to the nebula. Those with large light buckets should strain their eyes for the dimmer arcs of nebulosity surrounding all three stars. Good luck!

ngc 2343 is a coarse and fairly bright open cluster about 8^{^} northeast of dazzling Alpha (a) Canis Majoris (Sirius), the famous Dog Star. I first encountered it in November 2002, while trying to locate one of Caroline Herschel's lost deep-sky objects (NGC 2349) near the northern border of Canis Majoris and the southern border of Monoceros with my 4-inch refractor. It was one of five open clusters that grabbed my attention in the 3^{^} field. I made the brightest and most alluring of these clusters (NGC 2353) the 40th object in my Hidden Treasures list and included it in Deep-Sky Companions: Hidden Treasures. But as I noted in that book, “I could have made any one of the objects a Hidden Treasure.”

I encountered NGC 2343 once again as I worked on the Herschel 400 list. Now it's time for this peppery little cluster – the second brightest and most alluring cluster in the NGC 2353 area – to be further recognized. NGC 2343 lies about 1½^{^} westsouthwest of NGC 2353 and can be seen in 7 ^ 50 binoculars from a dark-sky site. It's also the most conspicuous of four clusters in a 1^{^} area of sky: Collinder 465, a roughly 10th-magnitude asterism of dim suns 15⁰ west of NGC 2343; Collinder 466, a tiny 11th-magnitude cluster of 25 stars a little more than 10⁰ south-southeast of Col-linder 465; and NGC 2335, another rich, 7th-magnitude cluster with 57 suns nearly 1¾^{^} north-northwest of NGC 2343.

NGC 2343 and its four companions (but not NGC 2353) are aligned with the long curving emission nebula IC 2177, most commonly known as the Seagull Nebula, for its appearance in photographs. The Seagull Nebula actually comprises two main parts: the Seagull's head (Robert's Nebula), and its wings (Wolf 's Nebula).” (For a more detailed discussion of the Seagull Nebula and its parts see DeepSky Companions: Hidden Treasures, pp. 200–201.)

The nineteenth-century British astronomer Admiral William Henry Smyth called NGC 2343 a “double star in a loose cluster, under the Unicorn's chest. . . This is a scattered group of brightish stars, in an irregular lozenge form, and consists chiefly of three vertical rows, having four individuals each; several are of the 9th magnitude, and reddish.”

In 1930, Trumpler classified it as IIpn, meaning it's a detached and poor cluster of stars with little central concentration associated with nebulosity. The 104-million-year old cluster lies 3,400 light-years from the Sun and 65 light-years below the Galactic plane. At that distance, the cluster has a true linear extent of only 6 light-years. The cluster is poor, having some 50 members, of which one star (HD 54387) is a very possible giant member.

NGC 2343 is located in the direction of the Canis Major OB1 association – a region in the plane of the Milky Way where dust and gas are being compressed into new and massive stars. Astronomers believe the Canis Major OB1 association formed in the aftermath of a supernova explosion about l million years ago. This event occurred at the edge of a dense cloud of gas and dust that measured about three light-years wide and had a mass of about 1,000 Suns. Then, about 100,000 years ago, the propagating blast wave from that explosion slammed into another cloud of dust and gas, triggering star formation that continues to this day in a region known as Canis Major R1 – a lean and extremely youthful star-forming region 100 light-years in extent.

Canis Major R1 appears to follow the Seagull Nebula, which itself is part of a larger ring nebula (Sharpless 296) that includes the Seagull Nebula (the curved western portion of the ring) and the nebula LBN 1036 near NGC 2353 along the ring's eastern boundary. And though it's uncertain, this large ring of emission nebulosity may be a relatively old supernova remnant; however, it could also be an old HII region blown out by stellar wind.

In a 1986 Soviet Astronomy (vol. 30, p. 648) the late Tamara Borisovna Pyatu-nina (Institute of Applied Astronomy, St. Petersburg) and Yu M. Taraskin (Special Astrophysical Observatory, Pulkovo) note, “in all likelihood four generations of stars coexist in [the Canis Major OB1 and R1 associations]” with NGC 2343 and NGC 2335 being the oldest generation, followed by NGC 2353, then the Canis Major OB1 association, and, finally, the youngest Canis Major R1 association. “All these different stellar generations probably are not just occupying the same region but are physically related to one another, constituting separate phases of a sequential starforming process, operating within a single complex of dust and gas.”

Indeed, Pyatunina and Taraskin say that radio observations confirm that the field contains a massive molecular cloud of intricate structure. NGC 2343 also matches an extended radio feature, which they find interesting. While it could be a coincidence, the researchers argue, “while a massive young cluster containing OB stars that ionize and heat the gas would tend to destroy the surrounding ‘parent' cloud, an old cluster whose OB stars have gone through their evolution would cease to heat the ambient gas but would serve as a ‘gravitational well' for it – a cell of recurrent condensation.” Thus, they conclude, the ionizing gas near NGC 2343 is being drawn there from outside sources in the Canis Major OB1 association.

To find this interesting cluster, it's best to first find NGC 2353. First locate Sirius on the chart on page 146, then the two 4th-magnitude stars marking the top of the Dog's head: Gamma (g) and Theta (y) Canis Majoris. Fifth-magnitude Mu (m) Canis Majoris lies midway between, and a little southwest of, those two stars. Using your binoculars, draw an imaginary line from Sirius though Mu, then extend that line about 6^{^} to the northeast; you should encounter three 6th-magnitude stars in an arc only ¾^{^} long and oriented north-northwest–south-southwest. The middle of these three suns is NGC 2353. Look for a 6th-magnitude star caught in a web of nebulosity – in this case, the “nebulosity” is that of unresolved starlight. Now use the chart on this page to locate NGC 2343 about 1½^{^} to the west-southwest just 35⁰ southwest of 6.5-magnitude Star a.

At 33^ in the 5-inch, NGC 2343 at first glance appears as a sparkling pyramid of starlight that consists of about a halfdozen irregularly bright suns, with a few outliers. The pyramid's brightest star is yellow 8.5-magnitude ADS 5817, which

W

marks the pyramid's southeast corner. With averted vision, a dim, roughly 10th-magnitude sun can be seen mirroring the pyramid's apex to the south, transforming it into a diamond or a cross, with the 11th-magnitude sun being the foot of the cross.

At 60^, the cross asterism stands out prominently (more prominently than you might see in photographs). A meandering, north–south oriented, stream of faint starlight flows through the pyramid, joining the top of the cross to its foot and forming the cross's vertical beam. The star marking the cross section of the two beams is a fine wide double. A wider pair lies just to its north inside the northwest quadrant of the pyramid. A number of dim suns pop into view with averted vision to the west of that latter pair. And three dim suns form a long and graceful arc over the top of the cross, from east to west, transforming the cross and the arc into a celestial hieroglyph.

The view is glorious at 94^, when many of the single suns can now be seen as double or multiple pairs. For instance, the double star at the intersection of the cross's beams has a faint companion to the southeast. And the double star north of it has a fainter double star to its southwest with another pair of stars to its westnorthwest. The longer I look the more pairs I see. (All this is magnified even more dramatically at 165^.) Most beautiful is the 11th-magnitude companion to ADS 5817, just 11⁰ to the northeast. Like me, Admiral Smyth saw the primary as yellow, and the secondary as “dusky.”

In fact, each corner star of the pyramid is a multiple; the star at the pyramid's southwest corner has a close pair of suns to its west-southwest and, if you look carefully, another pair continues in a stream to the southwest of those stars. And the top of the cross has a wide and faint companion to the north of it. The middle star in the lower part of the cross's vertical beam is double, as is the middle star in the northern arc over the cross! Owing to the cluster's wealth of double and multiple stars, I call it the Doublemint Cluster – in deference to the “refreshing taste of Doublemint™ gum,” which, at least when I was a kid in the 1960s, was advertised to double your pleasure.

All in all, NGC 2343 contains about 30 obvious stars 8th-magnitude and fainter in an area only 6⁰ across. Larger scopes will have a better view of the dimmer companions and will pick up twice as many members. By the way, if you can mentally lose the pyramid image in your mind and look at the cluster with north up, you'll see, just as Admiral Smyth describes, that the cluster does indeed comprise three major rows of stars, all roughly oriented northnorthwest–south-southeast. See if you can make them out.

While in the area, be sure to admire the Seagull Nebula, which is unmistakable in the 5-inch at 33^. The glow hardly needs any effort to see. It just “is.” I'm always amazed at the clarity of this ghostly visage – such a graceful and luminous arc of nebulosity.

ngc 2346 is an interesting bipolar planetary nebula riding the Celestial Equator in Monoceros, just 40⁰ west-southwest of 4.5-magnitude Delta (d) Monocerotis. It's one of the few planetaries with a central star that is visually more prominent than its surrounding nebula (when the star, which varies in brightness, is at maximum light), at least as seen through backyard telescopes.

Larry Mitchell of Houston, Texas, notes that there was some uncertainty as to whether the polar declination Herschel recorded in his original notes was 90^{^} or 91^{^} . The 6.5-magnitude star following the nebula was supposed to be 22 Monocero-tis, but the observed polar declination of this star must be 1^{^} wrong, as the “P.D. piece” was immediately afterwards set from 88^{^} 50⁰ to 89^{^} 48⁰ , “supposing it to have been set upon the wrong degree or changed by some accident.”

While William Herschel first noted the nebulosity surrounding the star in 1785, it wasn't until 1946 that Rudolph Minkowski at Mount Wilson Observatory classified it as a planetary nebula in the modern sense; he determined the nebula's true identity on the basis of its appearance on direct photographs obtained at the Newtonian focus of the 60-inch or 100-inch telescope.

In 1973, Lubos Kohoutek and G. Senkbeil found that the nebula's bright central star is spectral type A, and therefore not hot enough to excite the surrounding nebula, which requires an ionizing radiation of at least 45,000 K. Thus, the team proposed that the central star is a binary system, comprising an A0 III main component and a blue (O) subdwarf (the actual planetary nucleus). They also commented on the remarkable similarity of NGC 2346's nucleus to that of NGC 1514 (Secret Deep 15).

Today, astronomers accept that theory, advancing that the subdwarf has a sufficient temperature (100,000 K) to have ionized the nebula. The two stars closely orbit one another with a period of about 16 days. This is so close that even the Hubble Space Telescope could not resolve the pair. The Type-A component is also a variable known as V651 Monocerotis; it was not noticed to be variable until deep eclipses began at the end of 1981. These continued with a period of 16 days (the orbital period of the central pair). The variability, however, remained a mystery because the hot dwarf was thought to be too small to cause the large drops in brightness (the star can vary from magnitude 11.2 to 13.5 or fainter). This was eventually explained as a cloud of material moving across our line of sight. But after 1986, the eclipses stopped occurring until a dramatic series began 10 years later. The eclipses were still occurring in 1997 when the Hubble Space Telescope imaged the nebula, when the central star was barely visible (see the HST image above right).

Astronomers now believe that millions of years ago one of the two stars (the more massive one at the time) expanded to become a red giant, swallowing its less-massive companion, causing it to spiral ever closer in toward the more massive star, where it orbited inside its swollen envelope. In the process, rings of gas were expelled from the red giant. Most of the outer layers were ejected into a narrow but dense central waist (oriented east– west) surrounding the central star (see the Hubble image). As the hot core of the red giant was gradually uncovered, powerful stellar winds inflated two huge bubbles of gas that expanded perpendicular to the torus, producing the nebula's classic butterfly shape, whose major axis is inclined about 23^{^} to the line of sight.

In a 2001 Astronomical Journal (vol. 122, p. 3293), Lorena Arias and Margarita Rosado (Astronomical Institute, Mexico City) found that this dense disk, or torus, is expanding at a velocity of 16 km/sec. The total diameter of the nebula is about one-third of a light-year, or 2 trillion miles, and its age is estimated to be only about 2,200 years young – about the time when the Greek mathematician and astronomer Apollonius passed away.

To find this little treasure, use the chart on page 151 to locate Delta Monocerotis, then switch to the chart on this page. From Delta, move about 30⁰ southwest to a pair of 8.5- and 9.5-magnitude stars (a), oriented northeast–southwest, and separated by about 5⁰ . NGC 2346 is only 10⁰ further to the southwest. Again, note that the visibility of the central star depends on how, and when, it is being obscured by orbiting clouds of obscuring matter. When faintest, the star may not be visible in your scope. When brightest, it will appear as a near twin to a field star only about 5⁰ to the west.

At 33^ in the 5-inch, NGC 2346 is visible with averted vision. It seems larger than expected because its light blends with three other nearby stars. It takes concentration to separate them. But increasing magnification will resolve the problem. I'd use as much magnification as your telescope can handle. The central star is visible, being surrounded by a tight torus, which, under severe scutiny, I can see it at 165^, the torus being elongated northeast–southwest. This becomes even more apparent at higher powers. Larger

NGC 2346

S

telescopes may show the nebula's short perpendicular lobes stretching to the northwest and southeast, but I could not dect them at any magnification through my small aperture.

T he region of sky 10^{^} northeast of Alpha (a) Canis Majoris (Sirius), the brightest star in the heavens, contains a rich stream of telescopic nebulae and clusters that can keep visual observers and CCD imagers occupied for nights on end. This region is one of my favorite winter haunts, and its wonders continually amaze me. NGC 2359 is one of the more remarkable nebulae in that region. I don't know how this beauty escaped my attention prior to the creation of the Secret Deep list. Nevertheless, this fantastic wash of nebulosity has numerous subtle structures visible to the eye, which blossom into a wonderland of delight when imaged through a CCD.

For some odd reason, I always thought this nebula was a deep southern object, but NGC 2359, in fact, lies a bit farther north than open clusters M46 and M47 in neighboring Puppis. In his book Astronomical Objects for Southern Telescopes, Ernst J. Hartung notes that 51 years after his father's discovery of the object, John Herschel compared it to “the profile of a bust (head, neck and shoulders).” Indeed, as you can see from the table above, the nebula has all manner of fanciful names; I like the “Flying Eye” moniker the best, since it spotlights the beautiful bubble of gas (the eye) nestled within wide wings of associated nebulosity. It's quite a remarkable sight in color CCD images, and one of the more exotic-looking nebulae in the sky.

NGC 2359 is an emission/reflection nebula excited by the powerful wind (about 2,000 km/sec) and chemically enriched radiation of the 11.4-magnitude Wolf–Rayet Star HD 56925 (WR7). Wolf– Rayet stars represent a rare evolutionary phase in the lives of massive stars during which they undergo heavy mass loss, typically on the order of 10^{^5} solar mass per year. Due to the chemically enriched radiation, they display an extraordinary spectrum dominated by emission lines of highly ionized elements.

During its main-sequence phase, the 25 solar mass HD 56925 carved a huge bubble into a rather dense warm molecular cloud (Sharpless 298) that partially bounds it. The 2.3-million-year-old ring-like nebula is centered on HD 56925 and has a mass between 700 and 2,400 Suns. At an accepted distance of 1,600 light-years, the filamentary bubble has a true linear extent of about 230 ^ 120 light-years. Strong winds streaming from the extremely hot (up to ~50,000 K) Type O central star are driving the bubble's expansion at about 12 km/sec.

At a 2001 IAU meeting, C. E. Cappa (Argentinean Institute of Radio Astronomy, Villa Elisa) and colleagues described their radio observations of neutral and ionized gas in NGC 2359. NGC 2359 appears to be associated with three molecular clouds. The mass of neutral gas associated with NGC 2359 is about 320 Suns, while the ionized, neutral, and molecular material in the surrounding region amounts to about 2,200 Suns. They found that the amount of ionized gas in the molecular cloud associated with the filamentary bubble indicates that it mostly consists of swept-up interstellar gas.

Two other molecular structures also appear closely related to the bubble: One includes an arc-like feature that closely surrounds the northern part of a streamer of diffuse gas pointing to the northwest, the eastern region of the filamentary bubble, and a southern bar with an associated filament (all these features mark the location of the ionization front); the other structure consists of clumps that surround a major part of the shell and the southern bar of NGC 2359.

In a 2003 Astronomy & Astrophysics (vol. 411, pp. 465–475), Jose Ricardo Rizzo (European Space Astronomy Centre) and colleagues detected three different velocity components to the gas in the NGC 2359 region. The researchers found that its kinematics, morphology, mass, and density are clearly stratified (like an onion) with respect to HD 56925. These multiple bubbles, they believe, tell us something about the recent evolutionary history of HD 56925; namely, that they're related to several different energetic events that have acted upon the surrounding circumstellar medium. From the analysis of the massloss history of HD 56925, they suggest that the multiple layers of shocked molecular gas are likely to be produced during the earlier luminous blue variable phase and/or the actual Wolf–Rayet stage of HD 56925.

To find this delightful bubble of gas and its associated optical structures, use the chart on page 155 to first locate Sirius, then 4th-magnitude Gamma (g) Canis Majoris, the easternmost star in the Great Dog's head. Now use your naked eye or binoculars to locate the 5.5-magnitude Star a,3^{^} to the east, next to which is open star cluster NGC 2360 (Caldwell 58). Then look about 1½^{^} to the northeast for similarly bright Star b. Now use the chart on this

page to look for NGC 2359 about 1¼^{^} northnorthwest of Star b, about 1¼^{^} west of the 8th-magnitude open cluster NGC 2374.

At 33^ in the 5-inch the nebula is very obvious, with the first impression of it being a large, ~10⁰ -long elliptical patch, oriented roughly east-northeast–southsouthwest, punctuated on the eastern end by a roughly 11.5-magnitude star. A pretty 5⁰ -long chain of four 9.5- to 10.5-magnitude suns lies to east-northeast of this bar of light and parallels it. With time and averted vision, I detected the nebula's “eye” – rising above the eastern section of the southern bar to the northwest – like one of the cauliflower heads of a cumulus cloud. Averted vision also showed several dim stars swimming in and around the northern section of the bubble.

The nebula has a low surface brightness, so I found that, at least in the 5-inch, it doesn't take magnification well. I found the best view to be at 60^. At this magnification the southern bar is most distinct, with a faint extension to the northeast, though following it or defining it in any way was extremely difficult. Averted vision just shows an amorphous diaphanous glow of ill-defined light. The bubble is well defined, appearing as a filled-in ring of light with slightly sharper edges. It's somewhat detached from the southern bar but connected nevertheless by patches of faint light. I could not detect any of the fainter emission filaments like the one extending to the northwest from the north side of the bubble, nor could I see the filament extending to the west of the southern bar. The 11.4-magnitude Wolf–Rayet star is visible within the shell, along with a fainter “companion.” An arc of three similarly bright suns follows the northern curve of the bubble.

Of course, CCD images bring out all manner of detail. The Eye is filled with wispy filaments, the brightest emission

comes from the southern bar, which has a crab-leg-like bend that narrows to the west. Fainter filaments of gas can be seen to the east and northwest of the Eye, while vast washes of emission lie well to the northeast and southwest, among other structures both delicate and clumpy. Have fun exploring!

ngc 2371-2 is a dim, low-surface brightness planetary nebula 1½^{^} north of 4th-magnitude Iota (i) Geminorum. As with planetary nebula M76 (NGC 650–1), Herschel resolved this object into two parts (thus the double NGC number). The southwestern lobe is NGC 2371, the northeastern one is NGC 2372. Unknown to Herschel, these parts belong to a single nebula, one he did not recognize as a planetary because, simply put, when seen together the entire form resembles a dumbbell or butterfly more than a circular planet like Uranus.

Heber Doust Curtis (1872–1942) first recognized NGC 2371-2 as a planetary nebulae (Publications of the Lick Observatory, vol. 13, part III, 1918). He based his opinion on the object's characteristic appearance, which included the nebula's symmetry around a central star, on plates taken with Lick Observatory's Crossley reflector. His image of NGC 2371-2 shows two central lobes forming an irregular and patchy oval and two faint wings of exterior matter.

These outer wings are quite extensive, measuring about 2⁰ in apparent diameter, which, at an estimated distance of 4,300 light-years, means that the nebula's true physical extent is 3 light-years across – three-fourths the distance between the Sun and Alpha (a) Centauri. The inner lobes are one-third that size. Indeed, NGC 2371-2 is one of the largest planetary nebulae known.

The nebula's central star is rather faint (14.8), though not beyond the realm of moderate-sized backyard telescopes, and its spectrum shows strong emission lines that belong to the OVI class – very hot stars located toward the blue end of the post-asymptotic giant branch in the Hertz-sprung–Russell diagram. NGC 2371's white dwarf central star has a seething surface temperature of 130,000 ^{^}C with a luminosity ranging between 700 and 1,400 Suns.

OVI central stars are also nonradial pul-sators – only 16 of which are currently known. These rare planetary nebulae nuclei have distinct spectral lines with OVI emission at 3811 and 3824 angstroms. These lines can be either narrow and resolved or broad and blended. But only the central star of NGC 2371-2 shows both kinds of lines simultaneously, narrow features set atop a strong broad blend. NGC 2371-2's central star also displays slight magnitude variations with a period of about 17 minutes.

In November 2007, as part of the Hubble Heritage program, the Hubble Space Telescope took a strikingly detailed image of NGC 2371-2 (shown above right), with north to the lower right and east to the lower left). The image, which shows an area equal to 1.6 light-years, shows the nebula's bright inner lobes and one of the exterior “wings,” part of a huge halo of gas, which may be excited by ultraviolet radiation streaming out from the hot central star via a dark lane.

Most remarkable, however, are the prominent bright clouds and spots (which appear pink in the color image) in the two central lobes. These are relatively cool and dense knots of gas and may be jets of material ejected from the star along its rotation axis. Space Telescope Science Institute astronomers note, however, that the jet's direction has changed with time over the past few thousand years.

While the reason for this behavior is not well understood, it might be related to the possible presence of a second star orbiting the visible central star, causing the system's rotational axis to shift, affecting changes in the nebula's morphology.

In a 2008 Bulletin of the American Astronomical Society (vol. 40, p. 206), Douglas N. Arion and coworkers (Carthage College) note how their deep [OIII] images of NGC 2371-2 with the Steward Observatory 61-inch Kuiper telescope also show a broad range of filamentary structures permeating the entire nebula.

To find NGC 2371-2, use the chart on page 160 to locate Iota (i) Geminorum, which forms the southwestern apex of an isosceles triangle with the 1st-magnitude stars Alpha (a) and Beta (b) Gem. Less than 1^{^} northeast of Iota Geminorum are the 5th-magnitude stars 64 and 65 Geminorum. Center 64 Geminorum in your telescope at low power then switch to the chart on this page. From 64 Geminorum, make a generous 1^{^} sweep east-northeast to a crooked Y-shaped asterism of five 6th- and 7th-magnitude stars (a). Now move 50⁰ northwest to a pair of roughly 8.5-magnitude stars (b). A 25⁰ hop to the north-northwest will bring you to an arc of three 7.5- to 8.5-magnitude stars (c). Now move 30⁰ northwest to 7.5-magnitude Star d, which lies at the northeast end of a 15⁰ -long crooked line of slightly fainter suns. NGC 2371-2 lies only 35⁰ west and slightly north of Star d. Use the stars in Mario's image on page 161 to identify the field of faint stars that lie around the little planetary nebula.

Remember, to claim this prize, you must resolve the nebula into two bright patches. The key to success for small-telescope users is to be under a dark sky, know exactly where to look, and use high power with averted vision. If you still have

trouble, try gently tapping the tube. Plan to spend some time with this object. If you're patient, chances are you'll succeed.

At 33^ in the 5-inch (and once I knew where to look) I could glimpse the nebula with averted vision as a tiny bit of fuzz 1⁰ -wide. Increasing the magnification to 60^ reveals the nebula's elongated nature, being oriented northeast–southwest. NGC 2371-2's binary nature is quite apparent at 94^, appearing as two distinct orbs divided by a clean dark lane, oriented northwest–southeast. If you have a large amateur instrument, try looking for the nebula's fainter exterior “wings” to the northwest and southeast. I could not see them in the 5-inch. I find the view at 180^ very comfortable.

I have not yet detected the planetary's central star, but I encourage you to try, especially if you have a larger instrument that can handle power well. In their Observing Handbook and Catalogue of Deep-Sky Objects (Cambridge University Press, 1998), Christian B. Luginbuhl and Brian A. Skiff note its presence at 225^ in a 12-inch telescope. They also note that NGC 2371 (the southwest lobe) is slightly brighter than NGC 2372, having what appears to be stellar nucleus. Could this be the “jet”?

By the way, at 58⁰⁰ in apparent diameter, the bright inner lobes measure 1 light-year. So this would be a great object to show friends and guests at star parties who want to “see” a light-year.

ngc 2420 is a somewhat dim but very beautiful, rich, and finely spun open cluster about 6½^{^} south-southwest of 1.5-magnitude Beta (b) Geminorum (Pollux), the southeastern Twin star. It's also a little more than 2¼^{^} east-northeast of NGC 2392, the Eskimo planetary nebula (Caldwell 39) in Gemini.

I'll never forget my first encounter with it many years ago during a sweep of the heavens with the 9-inch f/12 Clark refractor at Harvard College Observatory in Cambridge, Massachusetts. I was comet hunting. Although the skies were a bit light polluted at thetime(IcouldstillseetheMilkyWaydimly on the best nights), I was certain I could nab a new comet shining brighter than 10th-magnitude, with an 8th-magnitude object being quite the comfortable sight ina sweep. One night while moving the great refractor slowly eastward beyond the southern arm of the Twins, I saw a round cometary form (about 8th magnitude) enter the field. My heart stopped; the diffuse object looked so stunning against the mottled starlight in the field – like a little fuzzy snowball. (The late Harvard astronomer Fred Whipple had, in 1950, referred to comets as “dirty snowballs,” so my imagining seemed appropriate.)

But on closer inspection, I saw the “comet's vapors” twinkling with averted vision. When I increased the magnification, the “vapor” shattered into a myriad of tiny scintillating gems. A look at a star atlas confirmed that I had found open cluster NGC 2420. Nevertheless, I have since became truly fond of this “twinkling comet.”

NGC 2420 is another astrophysically interesting open cluster. Trumpler classified it as type I1r, meaning it's a moderately rich, detached cluster with little central concentration whose stars exhibit a medium range in brightness. It's also an old cluster with an age of about 2 billion years. Only a handful of open clusters in our Milky Way are known to be more than 1 billion years old. So NGC 2420 joins an elite group of senior Galactic cluster residents, including NGC 752 (Caldwell 28) in Andromeda (~1.7 billion years), M67 in Cancer (~4 billion years), and NGC 188 (Caldwell 1) in Cepheus (~5 billion years).

Unlike many open clusters, which lie in the plane of the Milky Way, NGC 2420, which is about 35 percent farther from the Galactic center than our Sun, lies about 3,000 light-years above the main disk. What's more, while NGC 2420's age is about one-third that of our Sun, the cluster's average composition seems to be very similar to the Sun's.

In a 2002 press release from Kitt Peak National Observatory, Emily Freeland (Indiana University) – who, with her colleagues made new observations of NGC 2420 with the refurbished WIYN 0.9-meter telescope at Kitt Peak National Observatory, as part of a long-term project called the WIYN Open Cluster Study – says, “It is unclear how a cluster that is as rich in chemical elements as the Sun is can have such a location and motion around the Galaxy. Such clusters usually lie right in the Galactic disk.”

The researchers remain puzzled. It's possible, they say, that NGC 2420 formed in the disk but got ejected to its present location by a close encounter with a massive object (such as a giant molecular cloud), but it's not readily apparent how such an encounter could toss the cluster to such a high Galactic latitude. Another possibility is that NGC 2420 didn't originate in the Milky Way but in a dwarf galaxy that the Milky Way cannibalized.

“One problem with this idea,” notes Constantine Deliyannis, a WIYN Open Cluster Study team member from Indiana University and Freeland's research advisor, “is that small galaxies of this type are generally believed to be less rich in the chemical elements than the Sun. How could this little galaxy generate such a high abundance of heavy elements?”

The research team determined that the cluster contains 1,000 members out to 30 light-years. (Most catalogues attribute only about 300 members out to 15 light-years.) They also found a very clear main sequence (stars like our Sun that convert hydrogen into helium in their core), subgiant and giant branches (stars that have exhausted their core hydrogen), a red clump (giant stars converting helium into carbon in their cores), and blue stragglers (stars that appear younger than they should and may be the product of two suns merging into a single star).

NGC 2420 also contains a significant population of binary stars, with a surprisingly large fraction of these binaries being “twins” of roughly equal mass. “Other star clusters don't seem to have nearly as many twins,” Deliyannis says. “This interesting result, together with studies of the general distribution of binary mass fractions, will teach us about the environments in which stars and star clusters form.” Indeed, the researchers believe that NGC 2420 may contain a multitude of clues about the history and evolution of the Milky Way.

To find NGC 2420, I like to first find NGC 2392, Eskimo Nebula. Use the chart on page 165 to locate Delta (d) Geminorum ( Wasat). Note that Delta Geminorum is the bright star at the northwest end of a 2½^{^} -wide kite-shaped asterism with the 5th-magnitude stars 56, 61, and 63 Geminorum. Use binoculars to verify this appearance. Now center 63 Geminorum at low power in your telescope, then switch to the chart on this page. NGC 2392 lies just 40⁰ southeast of 63 Geminorum and 1.6⁰ due south of an 8th-magnitude star. Now, after you enjoy this delightful planetary nebula, make a slow and careful sweep about 55⁰ northeast to 7th-magnitude Star a. Now look about 35⁰ east and slightly south of Star a for 9th-magnitude Star b with a roughly 10th-magnitude companion. NGC 2420 is about 50⁰ east-northeast of Star b.

At 33^ in the 5-inch NGC 2420 is at a glance a round ghostly apparition of largely uniform light, like a tailless comet that gets gradually brighter in the middle. The glowing cluster is neatly framed inside a crooked Y of 9th- to 10th-magnitude stars. With averted vision, the glow transforms into an irregularly round blaze of tiny glittering gems, about a dozen or more of which seem to shine between 11th and 12th magnitude. It's hard to tell exactly, there is so much starlight that tiny bits seem to blend into more prominent ones, though this could be a trick of averted vision. At 60^, the core looks like a wet tulip glinting flecks of moonlight. The tulip is narrow on the southern end and fans out to the north; it is surrounded by a filamentary background of dimmer suns, as if diamond dust has been blown away from the cluster's core in all directions. At 94^, the wet tulip has a smaller sideways Y-shaped asterism of suns, oriented east– west; this smaller Y opens to the west. Again, the intriguing core is surrounded by a faint noisy background of cluster outliers; they seem to flit about in a halo that appears to extend beyond the cluster's 6⁰ diameter.

ngc 3079 is a spectacular, edge-on galaxy 64 million light-years distant in the Ursa Major Southern Spur of galaxies. It lies about about 3½^{^} south-southeast of 3.8-magnitude Upsilon (u) Ursae Majoris, in the Great Bear's foreknee. As seen from mid-northern latitudes, the galaxy never sets, though it's highest in the sky after sunset during the spring.

In high-resolution images taken with large telescopes, the galaxy is an awesome sight, displaying a bright nucleus in a lensshaped maelstrom of galactic vapors – a sight that brings to mind the “phrensied convulsion” described by Edgar Allan Poe in his A Descent into the Maelstrom:

Here the vast bed of the waters, seamed and scarred into a thousand conflicting channels. . . gyrating in gigantic and innumerable vortices, and all whirling and plunging on the eastward with a rapidity which water never elsewhere assumes except in precipitous descents.

The galaxy's central lens is surrounded by a seemingly warped disk, which, in the whole, makes NGC 3079 look like a phantom frisbee. The warp is largely an illusion created by dark dust irregularly distributed throughout the galaxy. The outer portions of its disk, however, have been distorted by tidal interactions with its two dwarf companions: 13th-magnitude NGC 3073, 10⁰ to the west, and a fainter anonymous companion nearly 6.5⁰ to the northwest.

Although we view NGC 3079's disk only 2^{^} from edge on, we can still see its central,

NGC 3079 is also one of the nearest and brightest Type 2 Seyfert galaxies known. Consequently, its nucleus burns with starlike intensity. As typical of Type 2 Seyferts, spectra of NGC 3079's nucleus are dominated by narrow-line emission. It has been argued, however, that all Type 2 Seyferts are intrinsically Type 1 Seyferts whose broad-line-emission component cannot be seen from our vantage point in space. Regardless, the spectra of all Seyferts indicate the presence of very hot, fast-moving gas close to that starlike active galactic nucleus (AGN) – most likely surrounding a massive black hole, which accretes gas from its surrounding environment.

Judith A. Irwin of Queen's University and D. J. Saika of the National Centre for Radio Astrophysics note that NGC 3079 is also unique among spiral galaxies, because it shows well-defined radio lobes extending from its AGN. It may be the closest analog of an extragalactic radio source (EGRS), providing a laboratory for understanding the relationship between starburst activity (such as that in M81) and the AGN in galaxies.

Indeed, in 2001, NASA released dramatic Hubble Space Telescope images of a lumpy bubble of hot gas, some 3,000 light-years wide, rising above the galaxy's disk from a cauldron of glowing matter within NGC 3079's core. The feature looks remarkably like a bursting lava bubble – a product of rapidly expanding gases within the melt. Indeed, it's theorized that NGC 3079's bubble formed about a million years ago when streams of particles rushing away from hot stars at the galaxy's core mixed with small bubbles of very hot gas expelled during supernova explosions, resulting in a burst of star formation.

Radioobservationsrevealthatgaseousfila-ments at the top of the bubble are still whirling around in a vortex and being expelled into space. Eventually, this gas will rain down upon the galaxy's disk where it may collide with gas clouds, compress them, and form a new generation of stars. These bubble bursts may be episodic, occurring about every 10 million years – until the hot stars expend their energy, depleting the bubble's energy source.

3079

3073 e

1˚

It may take some time to find this extragalactic wonder, because it requires some star hopping. First, use the chart on page 169 to locate the Big Dipper's Pointer Stars: Alpha (a) and Beta (b) Ursae Majoris, Dubhe and Merak, respectively. Now look about 10^{^} to the west for Upsilon (u) Ursae Majoris, which forms the apex of a nearequilateral triangle with Dubhe and Merak. Now use the chart on this page to find NGC 3079, which lies about 3½^{^} southeast of Upsilon. Begin by looking 2^{^} southsouthwest of Upsilon, where you'll find 5th-magnitude Star a. Next, move 1½^{^} east-northeast to 6th-magnitude Star b, which marks the southeastern corner of a nearly equilateral triangle with Upsilon and Star a. Now hop 40⁰ southeast to similarly bright Star c. From Star c, move 20⁰ south-southwest to magnitude 7.5 Star d. NGC 3079 is a little more than 50⁰ southeast of Star d, just 6⁰ northwest of a triangle of roughly 8.5- to 9.5-magnitude stars (e).

Years ago, in my 4-inch Tele Vue refractor, NGC 3079 was a somewhat difficult galaxy to see at 23^, appearing as a long and narrow streak of fairly faint light. But in the 5-inch at 33^, it was a fine sliver of light – 5⁰ long and oriented roughly north to south (with a slight tilt westward) – penetrating a tiny triangle of suns ( Triangle e on the chart). With concentration and averted vision, the galaxy's bright Seyfert nucleus pops into view surrounded by a central lens with a delicately mottled texture. The longer you look at it with averted vision (though be sure not to stare too long; it'll “drain” your eyesight) at this power, the more magnificent the galaxy appears.

At 60^, the inner lens stands out well, as does its Seyfert nucleus, while the galaxy's length appears scarred with light: two sharp, needle-like protrusions – one on either side of the central lens. With concentration, these needles appear isolated in the disk, surrounded by patches of dust. Indeed, at 94^, these arms give the galaxy's preceding side a sharp edge, while the entire disk (especially the nuclear region) is a maelstrom of faintly dappled light. As you gaze at this waver of extragalactic vapors, try imagining it receding from you at a speed of 1,116 km/sec (693 miles/sec).

ngc 3077 is a small but bright peculiar galaxy about 45⁰ east-southeast of the magnificent spiral galaxy M81 in Ursa Major, which has an equally dynamic companion, M82. NGC 3077 is a member of the M81 group, making it a well-known triplet of galaxies for small telescope users. Despite its apparent obscurity, NGC 3077 is just as bright and large as M89 (a much sought after elliptical galaxy in Virgo). This only helps prove the point that many non-Messier deep-sky objects are greatly neglected because they suffer the fate of being close to more visually overpowering sights, such as the powerful attraction of such a grand duet as M81 and M82. Yet our target is only a slight tap of the tube away from M81.

In the mid-nineteenth century, NGC 3077 was thought to be either an irregular lenticular (I0) galaxy or a peculiar mixed spiral lenticular galaxy (SAB0p). In plates, it appeared as a little elongated, smooth nebulosity marked by irregular patches of dark matter; two of them emerging on both sides near the minor axis simulate a nascent spiral pattern. The texture of the dust patches silhouetted against the galaxy's diffuse luminous glow is similar to that of M82 and NGC 5195 (Secret Deep 67).

Later images showed the irregular array of dusty filaments to have a roughly radial

pattern centered on the nuclear region. Other images also revealed some “knots” near the core, which were interpreted as either individual stars or star clusters, but their spectral luminosities were more like that of super star clusters.

Like its larger companion M82, the most unusual feature in NGC 3077 is that it's not well resolved into stars despite the small distance (10.4 million light-years). Astronomers postulated that if NGC 3077 is a starburst galaxy like M82, the activity, then, must be hidden (as in M82) presumably by dust.

Today we know NGC 3077 is a nearby dwarf starburst galaxy with a true linear extent of 20,000 light-years, a total mass of about 1.5 billion Suns, and a total luminosity of some 450 million Suns. In 2008, NASA released an incredible image that proved, the press release said, that “galaxies are like people. They're only normal until you get to know them.” NGC 3077 was part of a detailed survey, called the ACS Nearby Galaxy Survey Treasury (ANGST) program, in which astronomers used HST to observe roughly 14 million stars in 69 galaxies. The survey explored a region called the “Local Volume,” which spanned distances ranging from 6.5 million light-years to 13 million light-years from Earth. The image reveals in stunning detail (see above) not only a young massive star cluster with a mass of 200,000 Suns but also that the dark clumps of material scattered around the bright nucleus of NGC 3077 are pieces of wreckage from the galaxy's interactions with its larger neighbors.

Indeed, radio observations dating to 1978 have shown a bridge of neutral hydrogen gas extending northward from a large concentration in the southeast of the galaxy (seen inclined by 38^{^} from face on) toward the outer spiral arm structure of M81. But, as Walter Fabian (National Radio Astronomy Observatory, New Mexico) reported in 2002, the extended tidal arm of neutral gas near NGC 3077 is “one of the most dramatic features of its kind seen in the local universe.” It was created by an interaction with M 81 some 300 million years ago. It is one of the few tidal systems where atomic (HI) and molecular (CO) gas as well as low-level star formation (H-a) is detected over an area of several thousand square light-years. “This tidal complex,” Fabian says, “is believed to be in the process of forming a tidal dwarf galaxy.”

In 2003, deep Chandra X-ray observations of NGC 3007 resolved emissions from several supershells. About 85 percent of the X-ray luminosity in NGC 3077 comes from hot interstellar gas that stretches to the north but not to the south; the remainder comes from six X-ray point sources. Two years later, in a Monthly Notices of the Royal Astronomical Society, Mexican astronomer Daniel Rosa-Gonzalez made subarcsecond radio observations of the galaxy and found that one of the Chandra X-ray sources is associated with a supernova remnant (SNR) some 760 years old – between the average age of SNRs detected in M82 and those detected in the Milky Way and the Large Magellanic Cloud. The other X-ray source may be from an X-ray binary in the young, massive star cluster detected by HST.

At a 2009 American Astronomical Society meeting, Zhong Wang (Harvard-Smithsonian Center for Astrophysics) explained that a recent study of the star-forming regions in the tidal arms of NGC 3077, by him and his colleagues, revealed a gigantic shelllike structure that suggests an earlier starburst occurring on scales comparable to the galaxy itself. They also detected more than 30 HII regions previously identified in the immediate vicinity of this structure showing a common origin of shock disturbance. They proposed that gravitational interactions within the triplet (M81, M82, and NGC 3077) have not only torn away large amounts of HI gas from NGC 3077's mass center, but also induced large-scale star formation over a time scale longer than a typical bursting event.

To find this peculiar dwarf galaxy, use the chart on page 174 to locate 2nd-magnitude Alpha (a) Ursae Majoris. Now look 12^{^} to the northwest for 4.5-magnitude 24 Ursae Majoris. If you live under light-polluted skies, you may need to confirm the star with binoculars; notice that it forms the northeastern apex of a roughly 3^{^} -wide acute triangle with the similarly bright stars Rho (r) and Sigma (s) Ursae Majoris – actually this star marks the position of Sigma¹ and Sigma² Ursae Majoris.

Center 24 Ursae Majoris in your telescope at low power, then switch to the chart on page 177. From 24 Ursae Majoris, move 25⁰ southeast to 7.5-magnitude Star a. Next, move about 35⁰ further to the southeast to 6th-magnitude Star b. Bright M81 lies about 1¼^{^} east-southeast of Star b. Now look for the pair of 8th-magnitude stars (c) 40⁰ to the southsoutheast of M81. NGC 3077 is immediately southeast of the northeastern star in Pair c. It is best seen with magnification and looks like a small tailless comet. So be prepared to find the field then zoom in on your target.

At 33^ in the 5-inch, I could fit the triplet of galaxies in the same field of view. NGC 3077 was a bright but small (5⁰ -wide) uniform glow kissing an 8th-magnitude star. Its form is very circular and tight, looking like a concentrated puff of diffuse light like a cotton swab. With averted vision, I could see a distinct starlike core

and detect an out-of-round shape. At 60^, the galaxy takes on a more clearly elliptical form, and displays a very dense central core that gradually gets brighter toward the middle. The galaxy has a slightly mottled texture when seen with averted vision, with the northwestern side appearing slightly brighter, though this may be an illusion owing to the fact that the galaxy's southeastern side is closest to the 8th-magnitude star.

When you're done viewing NGC 3077, you may want to turn your attention to another forgotten wonder: NGC 2976, another member of the M81 group of galaxies, though it appears in a small telescope as only a dim ellipse of light. It's best viewed under a dark sky at low power. You'll need to take your time when searching for it, because the surrounding field has no bright stars. It lies about 1½^{^} southwest of the core of M81, less than 10⁰ northwest of a 15⁰ -long line of three 11th-magnitude stars (oriented northeast to southwest). I observed NGC 2976 in my smaller 4-inch Tele Vue refractor years ago, recording it at 33^ as a faint ellipse of diffuse light that almost vanishes with increased magnification. Larger scopes will reveal a mottled texture to the galaxy, which has no distinct central condensation. Yet the late deep-sky observing veteran Walter Scott Houston says he spied this 10th-magnitude galaxy in a 2.4-inch Unitron refractor, noticing it had a slight diamond shape. See what you think.

ngc 3166 and 3169 are two small, yet pretty, interacting galaxies less than 2^{^} south of 1st-magnitude Alpha (a) Leonis (Regulus). Although the pair lies about 3^{^} north of the Celestial Equator – so they stand halfway up the sky when highest in the south, as seen from mid-northern latitudes – they suffer from lack of attention owing to their lonely location in one of the classic voids of the night sky: Sextans, the Sextant.

Actually, Johannes Hevelius (1611– 1687) – who formed the constellation in 1687 from 12 unclaimed stars between Leo and Hydra (to honor the huge instrument he used in Danzig [now Gdansk] to make stellar measurements) – called it “Sextans Uraniae.” Hevelius placed the instrument between Leo and Hydra because, in the vernacular of astrologers, these beasts were fiery in nature. As Richard Hinckley Allen explains in his book Star Names: Their Lore and Meaning (Dover Publications, New York, 1963), William Henry Smyth said its placement “formed a sort of commemoration of the destruction of [Hevelius's] instruments when his house at Dantzic was burnt in September, 1679; or, as [Hevelius] expresses it, when Vulcan overcame Urania.”

The stars of Sextans are further doomed to obscurity by having no names associated with them, only Greek letters; even its Alpha star shines at a meek magnitude 4.5, faint enough to succumb to suburban light pollution. In his book Star Tales (University Books, New York, 1988), Ian Ridpath suggests, “it was perhaps to demonstrate the keenness of his eyes that [Hevelius] formed Sextans out of such faint stars.”

When William Herschel discovered NGC 3169 in 1783, he went on to make three additional observations of it before noticing that it hada companion (NGC 3166) only ~8⁰ away; how this other object, nearly equal in brightness, had escaped Herschel's attention for so long is a mystery, given the observer's acute ability to ferret out new nebulae – especially one so close to another.

William and his son John also failed to notice NGC 3165 only 4.5⁰ southwest of NGC 3166. But this isn't surprising; NGC 3165 shines at magnitude 14 and is only 1.5⁰ in apparent length. Still, as Brian Skiff and Christian Luginbuhl note in their Observing Handbook and Catalogue of Deep-Sky Objects (Cambridge University Press, 1998), NGC 3165 is “clearly visible” with averted vision as a “faint, difficult object” at medium powers in a 10-inch reflector.

Nevertheless, it took the visual prowess of R. J. Mitchel working under William Parsons ( Third Earl of Rosse) to pick out this tiny little object on January 30, 1856, with the 72-inch Leviathan at Birr Castle. Lord Rosse and his assistants excelled at discovering new nebulae near brighter known nebulae. NGC 3165 was but one of 233 nebulous objects they discovered between 1848 and 1865 with the 36-inch and 72-inch reflectors at Birr Castle.⁷

Dreyer listed NGC 3165 as GC 2037 in his supplement to the General Catalogue; French astronomer  E^´ douard

Jean-Marie Stephan at Marseille Observatory independently discovered it on March 18, 1884, with the 31½-inch reflector at Marseille. Stephan was obviously not aware that Lord Rosse's son, Lawrence Parsons (Fourth Earl of Rosse), had published the discoveries made at Birr Castle in an 1878 Scientific Transactions of the Royal Dublin Society.

All three objects (NGC 3166, NGC 3169, and NGC 3165) belong to the Leo Cloud of galaxies some 72 million light-years distant. NGC 3166 and NGC 3169, your targets, are receding from us at speeds of 1,345 and 1,238 km/sec, respectively. They have similar inclinations (58^{^} and 59^{^} , respectively) and true physical extents (97,000 and 93,000 light-years, respectively). They also share a common envelope of neutral hydrogen, suggesting tidal interaction. So the two are tugging twin systems.

NGC 3166 is the brighter of the two galaxies by a mere 0.2 magnitude in visual light (it is fainter than NGC 3169 in blue light), has a very small, very bright nucleus extending into a short smooth bar whose major axis is perpendicular to the major axis of the disk, which is oriented nearly east–west. The bar gives way to a disk of dust-lane fragments with no evidence for spiral features or star-forming knots. The disk resides in a lens surrounded by a weak extended envelope.

NGC 3169, on the other hand, has a very bright, flattened nucleus that extends some 3,000 light-years almost perpendicular to the plane of the galaxy. Paul B. Eskridge and his colleagues (2002) note that it may also have a weak bar (seen in the near-infrared) embedded in a large elliptical bulge, whose outer regions appear sightly boxy. As the Hubble Space Telescope image above shows, the galaxy's weak disk has a complex and varied dust morphology, from nuclear spiral lanes to chaotic feathery spiral features, all seen dramatically in silhouette against the galaxy's bulge. The disk also contains more than 60 HII regions, with some of them arranged in a shell-like structure that doesn't form a clear spiral pattern.

NGC 3169's most curious feature, however, is a highly distorted southeast spiral arm, suggesting that a tidal encounter has occurred between it and NGC 3166; NGC 3166's disk also shows peculiar tidal effects. The two galaxies reside some 100,000 light-years apart and are surrounded by an extended HI cloud more than 300,000 light-years across.

The envelope, which is centered on NGC 3169, surrounds not only NGC 3166 and 3169, but also NGC 3165. Indeed, in a 2006 Astronomy Letters (vol. 32, pp. 534–544), Russian astronomers Olga K. Sil'chenko (Sternberg Astronomical Institute, Moscow) and her colleagues note that they found the mean age of the stellar populations in the centers of all three galaxies to be approximately the same, about 1 billion years young. Since the galaxies are early-type ones, and since NGC 3166 and NGC 3156 show no global star formation, the astronomers suggest we are witnessing a synchronous star-formation burst in the centers of all three galaxies.

To find the celestial twins, use the chart on page 179 to locate 1st-magnitude Alpha (a) Leonis. About 25⁰ south of it is 4th-magnitude 31 Leonis. Now look about 35⁰ southwest for 5th-magnitude Pi (p) Leonis. Now use your unaided eyes or binoculars to locate 14, 16, and 19 Leonis, which form a 25⁰ -wide isosceles triangle about 45⁰ southeast of Pi Leonis. Center 19 Leonis, the southernmost star in that triangle, in your telescope at low power, then switch to the chart on this page. From 19 Leonis, make a generous, but slow and careful 1½^{^} sweep south and slightly east to an 18⁰ -wide triangle of 7.5- to 8.0-magnitude stars (a). NGC 3166 is less than 20⁰ north-northwest of the easternmost star in Triangle a. NGC 3169 is immediately to its north-northeast.

At 33^ in the 5-inch, the galaxies lie in a beautiful field, one rich in stellar pairs and groups. You'll find the pair about 25⁰ northeast of a 6⁰ -wide triangle of magnitude 7.5 to 8.5 stars, and about 15⁰ north of a 6⁰ line of magnitude 8 to 10 stars. While NGC 3166 is the brighter of the two, my eye is drawn first to NGC 3169 because it abuts an 11th-magnitude sun to the east, causing the eye to see an illusory larger object

19

3169 3166

3156

S

in that position. (This is probably why Herschel also noticed NGC 3169 first before he realized NGC 3166 was nearby.) Once I realized that there was a star next to the galaxy, NGC 3169 immediately shrank in splendor. It really is a tiny object, being only about 1⁰ in extent visually in my small telescope. So remember that you're looking for a little lens of light. Its disk is elongated northeast to southwest and has a small bead of light at its core. The galaxy's larger swooping and warped arms are much too faint for my 5-inch.

As I stare at NGC 3169, I cannot help but notice NGC 3166 to the southwest, which suddenly swells to prominence with averted vision. It's also hard to observe one, without comparing it to the other. The differences are quite striking considering the galaxies are “twins” in other respects. As I compared the two, it became immediately obvious that NGC 3166 is the slightly larger and brighter one. It also has a bright circular core that suddenly increases in brightness toward the middle where there shines a bright and stellar nucleus. At 94^, NGC 3166's elliptical disk is faintly apparent compared to NGC 3169's, which is more intense, a result of the galaxy's large central bulge. With averted vision, NGC 3169's central disk is a chaotic brew of light – various shades that swim in and out of view at the limit of visibility, leading to the impression of a misshapen and tortured nest of galactic vapors.

NGC 3169 has been the site of two known supernovae eruptions. The first (SN 1984E) was discovered visually on March 29, 1984, by Australian supernova hunter Robert Evans. It was learned, however, that three days earlier, Nataliya Metlova, of the Sternberg Crimean Station, had seen the supernova, as had Kiyomi Okazaki of Japan. The supernova was discovered near maximum light, which occurred on April Fool's Day. This Type IIL supernova (one that displays a linear decrease in its light curve) displayed the largest hydrogen luminosity ever seen from a single star; its light output was comparable to the luminosity of a spiral galaxy.

In 2003, amateur astronomers Koichi Ita-gaki of Japan, and Ron Arbour of the UK, independently discovered a 14.5-magnitude Type Ia supernova (one that lacks hydrogen and presents a singly ionized silicon line near peak light) 14⁰⁰ east and 5⁰⁰ north of the nucleus of NGC 3169. They discovered SN 2003cg near maximum light. Itagaki made his photographic discovery on March 21.51 UT; Arbour made his photographic discovery on March 22.835 UT.

By the way, in his Cycle of Celestial Objects, Admiral William Henry Smyth notes that NGC 3166 and 3169 are “on or near the spot where the Capuchin, De Rheita, fancied he saw the napkin of S. Veronica, in 1643, with an improved telescope which he had just constructed.”

He adds, “It would be much easier to ascribe this strange discovery to a heated imagination, than to deliberate falsehood; but it happens unfortunately that there is no staring cluster or nebula near.” He ends his discussion of this interesting observation by quoting Sir John Herschel: “Many strange things were seen among the stars before the use of powerful telescopes became common.” Can you find the napkin?

ngc 3198 is a somewhat “soft” and extended spiral galaxy about 2½^{^} northnortheast of 3rd-magnitude Lambda (l) Ursae Majoris ( Tania Borealis) in the Great Bear's left-hind foot, close to the northern border of Leo Minor. In fact, the galaxy belongs to the Leo Spur of galaxies. The great Irish astronomer Lord Rosse included NGC 3198 as one of his 14 “spiral or curvilinear nebulae” discovered prior to 1850; Lord Rosse initially described as “spiral” any object exhibiting “a curvilinear arrangement not consisting of regular reentering curves.”

In early plates, it was classified as a barred spiral galaxy, and many sources to this day refer to it as such. The early images of the galaxy revealed a small, very bright nucleus in what appeared to be a bar, partially obscured on one side. The galaxy also displayed what appears to be a pseudo-ring in the intermediate part of the galaxy's disk, and several knotty, partially resolved branching arms with numerous HII regions. The arms in NGC 3198 appear moderately thin and fairly well defined. However, the inclination angle of this 125,000 light-year-long system is so high (19^{^} from edge on) that the pattern is not easily traced.

In a 1991 Astronomy & Astrophysics (vol. 244, pp. 27–36) R. L. M. Corradi (University of Padua, Italy) and colleagues say that modern CCD images of the galaxy, however, have failed to reveal the presence of a bar. “Despite the RC2 classification,” they say, “there is no strong evidence that NGC 3198 is a barred spiral.” Their images show a “quite normal bulge” and an incomplete ring-like structure in the central region, noting that the spiral pattern appears complex because of the patchiness and the high inclination of the galaxy to the line of sight.

Given a more perfect viewing angle, we would probably see NGC 3198 as a twoarmed spiral with a secondary third arm. The two principal S-type arms would start at the center, then wind around for about half a revolution before each arm branched to form the multiple pattern we see in the outer regions. In a private 2010 communication, Bruce Rout explained that, through a geometric projection on each of the pixels in the image, the galaxy can be seen as if looking at it from directly above. “In this case we can see the galaxy as being a perfect Archimedean Spiral,” he shared.

The researchers, however, did not totally discount the possibility that deep infrared images might reveal a bar, which could be responsible for an observed “twisting” at the galaxy's core. Indeed, in an email, Rout informed me that “upon further research into the structure of galaxies, and from noting the ‘flat' velocity of rotation being 151 km/s, we can determine a small bar at the center of NGC 3198 having a radius of 12,500 ly. This is almost unnoticeable compared to the expanse of the entire galaxy which stretches for at least 300,000 light-years in diameter.”

Rout adds that NGC 3198 is quite a normal galaxy that orbits about its center of mass in a single plane of orbit, and its stars all orbit with a constant rotational velocity. He describes the arms of NGC 3198 as a “linear star cloud of nearuniform density which appears, from our local reference frame, as a non-uniform disc due to its rotation. The apparent non-uniform radial distribution of stars is described by delayed gravitational interactions over great distances in an accelerating reference frame whereby a uniform distribution of stars appears to occupy an increasing circumference.” He stresses that from “overwhelming evidence” in the observations of our own galaxy, “there is no requirement for exotic material [such as dark matter] in the linear mass distribution,” Rout says, as has been postulated by other astronomers. “Any material, exotic or otherwise, having a geometry other than that given by a linear mass distribution would invalidate a constant rotational velocity profile of material making up the galaxy. We therefore conclude there is no ‘dark matter' in NGC 3198.”

In the Hubble Space Telescope's key project, the Cepheid distance of NGC 3198 was determined to 47 million light-years. The team identified 78 Cepheid candidates in the period range from 8 to more than 50 days, of which 52 were selected for establishing the galaxy's distance. At that accepted distance, the galaxy has a true linear extent of about 40,000 light-years, a total luminosity of about 10 billion Suns, and a total mass of 60 billion Suns.

To find this object, users of small telescopes under somewhat light-polluted skies might want to first star-hop to the field, then use moderate magnifications to sight it. Light pollution will certainly impair the view, so try for it under the darkest skies available. Start by using the chart on page 185 to locate Lambda Ursae Majoris, center it in your telescope at low power, then switch to the chart on page 188. From

Lambda, move 18⁰ northeast to 6.5-magnitude Star a. Exactly 1^{^} due north of Star a is 6.5-magnitude Star b, which has a 9.5-magnitude companion immediately to its east. Now make a slow and careful sweep 1^{^} north-northwest to a pair of 7.5 and 8.0-magnitude stars (c). Another 1^{^} sweep, this time to the northeast, will bring you to a tighter pair of 9th-magnitude suns (d). NGC 3198 is about 15⁰ southwest of Pair m.

Under a dark sky at 33^ in the 5-inch, NGC 3198 is a big (nearly 10⁰ ) diffuse elliptical glow with a very nice diffuse concentration at the core but no starlike center.

With time and attention I could make out traces (or hints/suggestions) of the galaxy's high-surface brightness inner S-shaped arms. At 60^, NGC 3198 is a beautiful phantom of elongated light with the inner S-shaped arms more defined, emanating from a diffuse elliptical core with no further definition. At 94^, the core does sharpen in the middle to a brighter concentration of light, but even that is a diffuse speck of light. The arms are best defined at this power, and I could see enhancements at the bends in the S. Larger telescopes, however, will reveal the galaxy's sharp core and mottling throughout the disk.

Also, be on the lookout for supernovae. As of this writing, the last one (SN 1999bw) was discovered at 18th magnitude by the Lick Observatory Supernova Search on April 20, 1999 UT. Spitzer images of the object onMay 1 revealed that the shell's size is consistent with ejecta expanding at 1000 km/sec in the five years since core collapse, suggesting the reported emission may be from dust that condensed within the ejecta. NGC 3198 was the site of another supernova (SN 1966J), a prototype-Ib supernova, that had a peak blue magnitude of 11.2.