"Messier catalog." YourDictionary, n.d. Web. 18 December 2018. <https://www.yourdictionary.com/messier-catalog>.
Messier catalog. (n.d.). Retrieved December 18th, 2018, from https://www.yourdictionary.com/messier-catalog
A group of fixed nonstellar celestial objects originally cataloged by the French astronomer Charles Messier (1730–1817) and since expanded from 103 to 110, although several are now considered questionable. Items in the Messier catalog are numbered from M1 (the Crab Nebula) through M110 and include what are now known to be galaxies, nebulae, and globular and open clusters. Messier's purpose was to further the search for comets by listing the indistinct celestial objects that might be mistaken for them; he had no understanding of what the items in his catalog actually were.