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Messier catalog(mĕsyā`), systematic list of nebulae and star clusters. A first list, compiled and published in 1771 by Charles Messier, contained 45 objects. The final list, published in 1784, contained 103 objects; some of these were later removed from the list. Of the remaining objects, about 50 are extragalactic nebulae, i.e., galaxies. Designations from Messier's catalog are frequently used to refer to the brighter nebulae and star clusters; for example, M31 is the Andromeda Galaxy, M1 the Crab Nebula, M42 the Great Nebula in Orion, and M45 the Pleiades.
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Messier Catalog(mess -ee-ay, mess-yay ) A catalog of the brightest ‘nebulae’ prepared by the French astronomer Charles Messier and printed in final form in 1784. Messier compiled the list in order to avoid confusion of these cloudlike objects with comets, for which he was a keen searcher. 103 celestial objects, which appeared fuzzy and extended in telescopes of the time, were listed and given a number preceded by the letter M. This is the object's Messier number, an example being M42: the Orion nebula. It was later found that most of the objects were not true nebulae but galaxies and star clusters. Seven more objects were later added to Messier's list, bringing the total number of cataloged items to 110. See Table 8, backmatter; NGC.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006