MESSIER CATALOG

(M), in astronomy, list of approximately 109 star clusters, nebulae, and galaxies compiled by Charles Messier, who discovered many of them. The catalog is still a valuable guide to amateur astronomers, although it has been superceded by the New General Catalogue (NGC); both NGC numbers and Messier numbers remain in common use. The Messier catalog includes such diverse items as the Crab Nebula (M1), the Pleiades (M45), and the great spiral galaxy in Andromeda (M31). Messier's purpose was to make comet hunting easier by tabulating permanent deep-sky objects that could be mistaken for comets. He published a preliminary list of 45 such objects in 1771 and compiled the bulk of his catalog 10 years later. By 1784 he had listed 103 objects; in 1786 Pierre Mechain added 6 more. The existence of five Messier objects (M40, M47, M48, M91, and M102) is now considered doubtful.