parent/ Messier Objects Chapter1 Chapter2 Chapter3 Chapter4 Chapter5 Chapter6 Appendix
5 Some thoughts on Charles Messier
Charles Messier is best remembered for the objects he largely tried to avoid, and help others to avoid. Messier was first and foremost a comet hunter, and he dedicated clear, moonless nights to this pursuit. He was quite successful in his search, having found some 15 comets, though only 12 bear his name (with some exceptions, comet names were not officially used until the twentieth century). In his time, comet hunting was intensely competitive, and Messier was inspired not only by the search but also by the fame new comet discoveries would bring him. The fuzzy, no/zcometary objects he encountered intrigued him, in part, because they fooled him, if only briefly. Messier created his renowned catalogue largely to benefit comet hunters, so they would not confuse these nebulous glows with comets. But it's also possible Messier knew he would reap fame by discovering new nebulae.
Messiefs first list of 45 objects, published in the Memoirs of the French Academy of Sciences for the year 1771, was well received by his friends and colleagues. In the introduction to the work, astronomer Jerome de Lalande praised Messier, saying the task could only have been undertaken by an indefatigable and experienced observer. William Herschel, in particular, regarded Messier's catalogue as an excellent collection of clusters and nebulae, and it apparently prompted Herschel to undertake his own search for similar deep-sky objects. (Herschel employed much larger telescopes in his survey which led to the additional discovery of more than 2,000 objects.) Nevertheless, legitimate questions can be raised about why certain objects made it into Messier's catalogue and other seemingly obvious ones did not.
Messier was surprised to resolve stars in several objects described by lheir discoverers as nebulous patches. But if his aim was to help comet hunters avoid objects that might prove confusing, why would he include obvious open clusters, such as M23, M34, M45, and M47? Perhaps, because they appear fuzzy to the naked eye, he did so for the benefit of the naked-eye gazer. (It should be noted that in the mid-1700s spotting a new comet with the unaided eye was not uncommon.)
It would be fruitless to question the observing ability of the man described by King Louis XV as the "ferret of comets/' Messier was highly respected for his keen eye and attention to detail. His expertise was not limited to the visual search for comets, as he was an equally skilled observer of, among other things, the planets, stellar occultations, and sunspots. Still, one has to wonder how Messier could have missed so many relatively bright nebulous objects during his comet hunts. Anyone who takes the time to sweep the sky with a telescope around (he famed M objects cannot help but chance upon some nebulae and clusters that were not included in his catalogue, apparently escaping his gaze. But did they?
We know that of the 109 objects in the catalogue, Messier actually discovered 41 of them; the other objects had been found by others, but Messier recorded their pos让ions and appearance anyway since they could be confused with comets. Once he started the catalogue, Messier wrote, he endeavored to find other nebulosities; he made this something of a project for its own sake, at least in the beginning. But after the first catalogue of 45 objects was published, most of the objects recorded thereafter by Messier were found serendipitously, when particular comets he was following would happen to pass near a nebulous patch. On average, he discovered only about two new catalogue objects per year.
One particularly puzzling omission from the catalogue is the Double Cluster in Perseus. Why would Messier not include this conspicuous Milky Way object, which appears distinctly cometlike to the naked eye? Yes, the cluster does resolve with the slightest optical aid into a myriad of individual stars, but the same could be said of the Pleiades, the brilliant and easily resolvable open cluster in Taurus, which he catalogued as his 45th entry. His inclusion of the Pleiades makes it hard to argue that he considered some objects too obviously not cometlike in appearance to be confused by them, or to bother recording them.
One can only speculate about the absence of the Double Cluster and other bright objects of which we presume Messier should have taken notice, even with his rudimentary scopes. And one can perhaps detect a bit of defensiveness in Messier about his catalogue in some remarks he made in the French almanac Connaissance des Temps for 1801, just a few years before his death. After me, the celebrated Herschel published a catalogue of 2,000 which he has observed. This unveiling of the sky, made with instruments of great aperture, does not help in a perusal of the sky for faint comets. Thus my object[ive] is different from his, as I only need nebulae visible in a telescope of two feet [length]. Since the publication of my catalogue I have observed still others; 1 will publish them in the future ... for the purpose of making them more easy to recognize, and for those searching for comets to remain in less uncertainty." It would be informative to know Messier's feelings on this 30 years earlier. In Messiers Nebulae and Star Clusters Jones comments that the argument that large apertures do not help in the discovery of comets doesn't hold water. But I find Messier's remark about his objective being different from Herschel's, and his need to see only nebulae visible in a telescope of two・foot length, as testimony to what I believe was his unwavering purpose, the pursuit of comets.
It is also surprising that Messier could not telescopically resolve the great globular clusters M5 in Serpens Caput and M13 in Hercules. Of course, he was limited not only by the poor location of his observatory but also by the poor quality of the optics in his instruments. He used about a dozen different telescopes ranging from reflectors with inefficient speculum mirrors (the largest having an 8-inch aperture) to simple refractors with apertures of up to 3% inches. He generally employed magnifications of between 60 x and 138x. Compared to todays instruments, all these telescopes were of substandard optical quality "It is a pity/' wrote Smyth in his Cycle of Celestial Objects, "that this active and assiduous astronomer could not have been furnished with one ofthe giant telescopes of the present day.... One is only surprised that with his methods and means, so much was accomplished/' Likewise, Lalande could only lament that the precise and zealous Messier could not live under purer and less cloudy skies, which obviously hampered his abil让y to find new comets and nebulae.
Some of today's skilled comet hunters claim to have an innate sense of what a new comet will look like through the telescope. Thus, it is the comet huntefs prerogative to skip over or ignore whatever object he or she deems not cometary. It is reasonable to presume that Messier had his own criteria for judging whether an object was sufficiently cometlike in appearance to warrant noting its position* though he did not relate those criteria. But it should be said that he never endeavored to conduct a comprehensive visual search for noncometary nebulae. An old Chinese proverb tells us that obstacles are what we see when we take our mind off the goal. And Messiefs goal was to discover comets, not nebulae or star clusters. In contrast, Herschel's goal was to systematically survey the entire sky for deep-sky bounty beyond the limits of Messier's instruments. Most of the relatively bright non-Messier objects we enjoy today (at least from the Northern Hemisphere) were discovered by Herschel. There can be no doubt that had Messier conducted a similar deliberate search for noncometary objects, his catalogue would have turned out vastly larger and less haphazard than it is. But that was not Messier's concern, comets were. It is only by the fickleness of fate that none of his comets had the staying power of his catalogue of deep-sky wonders.