Comet Hunters and Catalogs

This Saturday the physics department hosted another astronomy open house, organized by yours truly. While it originally looked like we would have to cancel due to cloudy skies, it cleared up just in time! This month's theme was Charles Messier and his well-known astronomical catalog of the same name. I did a little research about him in preparation for my presentations, and here's what I found out.

Charles Messier is most known for the Messier Catalog, a list of 110 observational objects visible from the northern hemisphere. However, this catalog was really only a byproduct of his main focus, comet hunting. He was born in France in 1730, and at the age of 14 was fascinated by the appearance of the Comet de Cheseaux, a magnificent six-tailed comet. As a young adult, he worked for the navy astronomer before setting off on his own to discover new comets.

Comets, as you probably know, are relatively small, icy bodies that orbit the Sun (at least within our own solar system). The radiation coming from the sun can sublimate the ice and the atmosphere surrounding the comet, creating a "tail". Unlike the planets, comets tend to have highly elliptical orbits, so much so that many years or centuries can pass before they are observed a second time. This means that astronomers are always on the lookout for new comets!

The only issue is that to the casual observer looking through a small telescope, there are a lot of other objects in the night sky that can look like comets. Take a look at the comet below, followed by the Andromeda Galaxy and a star cluster:

In order to avoid confusion, Messier began a catalog of objects he observed that looked like comets but weren't. This list was published in a variety of forms, and eventually expanded to include 110 objects. Really, they don't have too much in common other than the fact that they are all extended objects (rather than stars, which would not be confused with comets), including galaxies, open and globular star clusters, and nebulae.

Nevertheless, Messier's detailed observations meant that any astronomer could use his numbering scheme to easily identify the objects in their own telescopes. These Messier objects often make excellent subjects for the amateur astronomer; the Orion Nebula, Andromeda Galaxy, and Ring Nebula are all included in his catalog.

In case you're wondering, Messier did actually discover several comets. However, he's now much better known for his catalog!