Messier 72 — Globular Cluster in Aquarius

M72 (NGC 6981) is a globular cluster in the constellation Aquarius, located approximately 55,400 light-years from Earth — one of the more distant Messier globular clusters. At magnitude 9.3, it spans about 6.6 arcminutes, corresponding to a true diameter of roughly 106 light-years. M72 is classified as concentration class IX, making it a rather loosely concentrated globular. The cluster contains an estimated 100,000 stars and has a moderate metallicity of [Fe/H] = -1.42. M72 contains 43 known variable stars, predominantly RR Lyrae types. The cluster's great distance makes it intrinsically quite luminous despite its modest apparent brightness. It lies on the far side of the galactic center from us, about 40,000 light-years from the center of the Milky Way, placing it in the distant outer halo. M72 is relatively isolated in the sky, located in a sparse region of Aquarius away from the Milky Way's rich star fields. About 1.3 degrees to the east lies M73, a tiny asterism of four stars that Messier cataloged on the same night.

Located in Aquarius, about 3 degrees south and slightly east of Epsilon Aquarii (Albali). M72 is one of the more challenging Messier globular clusters due to its distance and relatively low surface brightness. In binoculars, it appears as a very faint, small, round haze — easily overlooked. A 4-inch telescope at 100x shows a small, diffuse, unresolved glow. An 8-inch telescope at 150-200x reveals a slightly granular texture, but individual stars remain difficult to resolve due to the great distance. Resolving the outer stars requires 10-12 inches of aperture at high magnification under dark, transparent skies. Best observed from August through October. Located near M73 (just 1.3 degrees east), the two objects are often observed together.

Discovered by Pierre Mechain on August 29, 1780. Charles Messier observed and cataloged it on October 4, 1780, on the same night he cataloged M71 and M73. Messier described it as a faint nebula, and William Herschel later resolved it into stars. Due to its great distance and faintness, M72 was among the last Messier globulars to be thoroughly studied with modern techniques.