From Charles Messier, who first published Nebulae and Star Clusters in 1774 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.
- (astronomy) The Great Globular Cluster of several hundred thousand stars. It lies at a distance of approximately 25,000 light years from Earth, in the direction of the constellation Hercules. It is the brightest and best-known globular cluster in the northern skies.