Charles Messier was a French astronomer who lived from 1730 to 1817. He was a comet hunter. In the process of cataloging comets, he frequently stumbled across objects that, to him, initially appeared to be comets. He compiled a list of 110 of these objects, which is now called the Messier catalog.
These Messier objects are now well known to nearly all astronomers. Most of these are spiral galaxies or globular clusters. M57, also known as the Ring Nebula, is a planetary nebula.
When I first learned about the Messier catalog and the reasons behind its creation, I was a little confused. Why would someone make a list of things they are not looking for? I suppose it makes sense that if you are committed to a somewhat repetitive mental task, you would want to make it easier for yourself to avoid common mistakes. That is the likely initial purpose of the catalog.
I suppose that through an 18th century telescope, it might be a little difficult to distinguish between a comet, a galaxy, a globular cluster, and a planetary nebula. While telescopes did enable astronomers to see deeper into space than they had in the centuries before, 18th century telescopes are put to shame by their 20th and 21st century counterparts.
Messier cataloged galaxies centuries before we knew what galaxies really were. It was not until the 1930’s that Edwin Hubble proved conclusively that they were, in fact, extragalactic objects and were millions of lightyears distant. In Messier’s time, people simply assumed that they were just nebulae.
Whatever the Messier catalog’s initial reasons for existing, it gives amateur and professional astronomers a great jumping off point for observing relatively nearby objects.