Curiosity 17: Messier objects

 I ran into this XKCD comic on FB today, and it tickled my funnybone:

The original post appended this comment: "The debate over the correct Messier number for the Ship of Theseus is ongoing."

So far, my post has gotten four likes—from a cartoonist, a mathematician, a pastor, and my eclectic SIL—so apparently the humor is a bit rarefied. I guess I just think it's funny that we humans feel compelled to count and catalogue everything.

In any case, Messier objects: what are they really? I had to look it up to get the facts right.

Briefly, they are celestial objects—galaxies, planetary nebulae, and star clusters—all observed by French astronomer Charles Messier (1730–1817). He became fascinated by astronomy as a boy when he saw the Great Comet of 1743/44 and then an annular eclipse in 1748. He grew especially interested to discover comets—he found 13 during his lifetime—but there were all these pesky "fixed diffuse objects" in the night sky that could be mistaken for comets. So he set about making a record of them—nailing them down, so to speak.

The first version of his Catalogue des Nébuleuses et des Amas d'Étoiles (Catalogue of Nebulae and Star Clusters), published in 1774, contained 45 objects, a good number of them already observed by others. The Crab Nebula, for example—number 1 in the catalogue—was first described by English astronomer John Bevis in 1731 (though it was no doubt observed as early as 1054 by Chinese sky-watchers, in the form of a supernova). When Messier initially mistook it for Halley's Comet, he realized there were probably other diffuse objects masquerading as comets, and so his task was born.  By 1781 he had published a list of 103, with subsequent additions by other astronomers bringing it to 110. 

Of course, Messier's ability to observe the night sky was limited by geography—he did all his observing from the Hôtel de Cluny in Paris—and technology—he used only a 100 mm (4-inch) refracting telescope. Other astronomers, including the English brother-and-sister team John and Caroline Herschel, continued his quest. The most recent iteration of Messier's initial project is the Complete New General Catalogue, compiled and revised and published in various versions over the years (most recently in 2019), containing 13,957 objects. 

Here are Messier's 110 objects all together (click to see large):

And here is a map of their locations in the sky of the northern hemisphere:

Cool, no?

P.S. The FB likes have now climbed to six, including one by my friend Andrew, who pointed to a short story by Jorge Luis Borges, "El idioma anolítico de John Wilkins" (The Analytical Language of John Wilkins). As one element of the story, Borges compares Wilkins's classification scheme to (I quote from the Wikipedia entry)

a "certain Chinese encyclopedia"..., said to divide animals into "(a) those that belong to the Emperor, (b) embalmed ones, (c) those that are trained, (d) suckling pigs, (e) mermaids, (f) fabulous ones, (g) stray dogs, (h) those that are included in the present classification, (i) those that tremble as if they are mad, (j) innumerable ones, (k) those drawn with a very fine camelhair brush, (l) others, (m) those that have just broken a flower vase, (n) those that look like flies from a long way off." Borges's point is the arbitrary nature of such taxonomies, regardless of whether they form a language or just a way of understanding and ordering the world. He challenges the idea of the universe as something we can understand at all‍—‌"we do not know what thing the universe is"—‌much less describe using language.

Borges's list, likewise, tickles my funnybone. At the same time, it is full of ontological and epistemological weight. I'm glad Andrew is so erudite.