Charles Messier (pronounced Mez-i-yay) is somewhat of an unsung hero to amateur Astronomy scene. He was a comet hunter, which he held 13 in his name which is a pretty good turnout given the fact that he was born in 1730 and the telescopes back then were less than perfect and he wanted to give something to his fellow hunters...a catalog. Most people would scoff at the notion of receiving a catalog as gift but Messier produced something a little different.
Messier noticed a problem that comet hunters were having during in the mid 1700's. Many comet hunters were all finding the same object and they were all publishing the same objects as comets. This would have proven disastrous because to have the same object with 20 different names could get confusing. So Messier went on a hunt to locate as many stationary, non star-like objects as possible with his 4" telescope. In 1774 he produced a catalog of 103 objects consisting of galaxies, nebula (however at the time, galaxies and nebula were thought to be the same thing and were called "grey fuzzies") and star clusters. Later on researchers found notes and evidence of 7 more object that he notated and today there are 110 objects in his catalog. This catalog prevented comet hunters from "discovering" the same object over and over again. The catalog also marked the position of stationary objects so comet hunters would not spend weeks if not months waiting for an object to move when in reality it was a galaxy.
What does this mean for us though? Well messier put the "M" in Astronomy. Have you ever looked at start charts and noticed objects titled "M31," "M42", "M45?" Have you ever been around Astronomy geeks and been confused because they never speak in complete sentences ie. M51 with low surface brightness at mag 9.2 in Canes Venatici? Well these are object that Messier cataloged (hence the "M" before the number due to Messier) and to this day it is one of the greatest catalogs for amateur astronomers around. Almost all of the objects can seen with a 4" or larger scope, easily locatable, and they keep on getting better with bigger telescopes. Today the Messier Catalog is a staple for anyone in Astronomy and it will probably stay that way for quite some time.
There are many other catalogs but that will have to be another post. For now if you are getting into astronomy, Messier will keep you occupied for quite some time.
FYI- each year around this time amateur astronomers have what is known as the Messier Marathon and the idea is to try to locate and see all 110 objects in one night. Its a great feat to accomplish but I wouldn't count on it as a credential for a job.