Messier 22 — Globular Cluster in Sagittarius

M22 is one of the brightest and nearest globular clusters visible from Earth, located about 10,600 light-years away in the constellation Sagittarius. It contains roughly 70,000 stars and spans about 99 light-years in diameter. At magnitude 5.1, it is the brightest globular cluster visible from mid-northern latitudes after M4. M22 has a slightly elliptical shape and a relatively loose structure for a globular, with a concentration class VII. The cluster is one of only four known globulars to contain a planetary nebula.

Located about 2.5 degrees northeast of the star Kaus Borealis (Lambda Sagittarii), at the top of the Sagittarius Teapot asterism. At magnitude 5.1, it is easily visible to the naked eye from dark sites. Binoculars show a large, bright, slightly oval glow. A 4-inch telescope at 100x begins resolving individual stars across the cluster. An 8-inch telescope at 150x produces a spectacular view with stars resolved throughout. From southern locations it is even more impressive. Best observed from July through September. Unfortunately, from mid-northern latitudes it remains rather low.

Discovered by Abraham Ihle in 1665, making it one of the first globular clusters ever discovered. Charles Messier cataloged it in 1764. The planetary nebula IRAS 18333-2357 was discovered within M22 in 1986. In 2012, two stellar-mass black holes were detected in M22 through radio observations.