The Messier Catalog

Charles Messier (1730-1817) was a French astronomer credited with creating a catalog of 110 objects which, for lack of a better description, might have been called “110 Objects In The Sky That Are Not Comets.”

Messier's occupation as a comet hunter led him to continually come across fixed diffuse objects in the night sky which could be mistaken for comets. He compiled a list of them, in collaboration with his friend and assistant Pierre Méchain (who may have found at least 20 of the objects), to avoid wasting time sorting them out from the comets they were looking for. The entries are now known to be 39 galaxies, 4 planetary nebulae, 7 other types of nebulae, and 55 star clusters.

The final version of his catalog was published in 1781.   The final list of Messier objects had grown to 103.   On several occasions between 1921 and 1966, astronomers and historians discovered evidence of another seven objects that were observed either by Messier or by Méchain, shortly after the final version was published. These seven objects, M 104 through M 110, are now accepted as "official" Messier objects also.

Sources:     https://en.wikipedia.org/wiki/Charles_Messier
     https://www.space.com/16686-charles-messier-biography.html
     https://www.britannica.com/biography/Charles-Messier
     https://www.astrosurf.com/re/messier1.html

** - Photo Credits:
        1 - Public Domain