A Messier Object is an astronomical object first described by the great French astronomer Charles Messier in 1771. An insatiable comet hunter, Messier began his catalog of objects that were neither stars nor comets as a way of accounting for them and subsequently avoiding them as he searched for comets. With the help of his assistant Pierre Méchain, the first edition of the Catalogue des Nébuleuses et des Amas d’Étoiles (Catalogue of Nebulae and Star Clusters) contained 45 objects, mostly nebulae, galaxies and star clusters. According to Messier, who was waiting for the return of Halley’s Comet:
What caused me to undertake the catalog was the nebula I discovered above the southern horn of Taurus on September 12, 1758, whilst observing the comet of that year. This nebula had such a resemblance to a comet in its form and brightness that I endeavored to find others, so that astronomers would no more confuse these same nebulae with comets just beginning to appear.
Messier’s final publication included 103 objects, but the catalog was added to as recently as 1966, almost 200 years after his original publication! Today the catalog contains 110 objects and many objects are still referred to by their Messier number.
All images in the public domain, courtesy NASA.