Messier 12 is a globular cluster in the Milky Way, around 16,000 light years away. It is located in the constellation of Ophiuchus close to M10, a slightly brighter globular cluster. It is not visible to the naked eye, but it can be seen with binoculars in good seeing conditions, appearing as a fuzzy grey patch. It was discovered on 30th May 1764 by the French astronomer, Charles Messier, but he was unable to resolve the cluster, so believed it to be a nebula. It was one of Messier's earliest discoveries. It was first resolved into stars by William Herschel in 1783 using a 7-foot telescope.

Messier 12 is a very loose globular cluster once believed to be a tightly concentrated open cluster. Most of its low-mass stars were carried away by the gravitational influence of the Milky Way. This is because globular clusters tend to travel in extended elliptical orbits, passing through dense regions of the galactic plane. Smaller stars can be ripped away by the large gravitational force to follow a new, independent orbit. It is estimated that it has lost four times as many stars as it currently has, so roughly one million stars would have been ejected into the Milky Way. It now has around 16,000 stars, many of these are up to 40 million times fainter than a star detectable by the human eye.