(astronomy): A catalog number used to name and record approximately 100 galaxies, nebulae, and other objects visible in the night sky that are not stars. Objects in Messier's catalog of Nebulae and Star Clusters are numbered, and the letter M (for Messier) is prepended to these numbers, as in M31 (the Andromeda Galaxy) or M13 (the globular cluster in Hercules).
Other Word Forms of Messier-number
Origin of Messier-number
From Charles Messier (1730-1817), who first published Nebulae and Star Clusters in 1780 as a listing of visible objects in the night sky that were not stars. Objects in Messier's catalog are numbered, and the letter M (for Messier) is prepended to these numbers.
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