Messier number

{{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).