M22 - SAGITTARIUS CLUSTER

Messier 22 is one of the brightest and nearest globular clusters in the sky, located approximately 10,600 light-years from Earth in the constellation Sagittarius. Shining at an apparent magnitude of 5.1, it is easily visible to the naked eye under dark skies and is a spectacular sight in any optical instrument. M22 contains an estimated 70,000 to 83,000 stars within a diameter of about 99 light-years and was one of the first globular clusters ever discovered, observed by Abraham Ihle in 1665, predating Messier's catalog by nearly a century. The cluster is remarkable for several reasons beyond its visual splendor. It is one of only four globular clusters known to contain a planetary nebula (designated IRAS 18333-2357), and radio observations have detected two stellar-mass black holes within it, the first such detections in any globular cluster. M22 also shows an unusual spread in chemical abundances among its stars, suggesting it may have undergone multiple episodes of star formation, a property shared with only a handful of the most massive globular clusters like Omega Centauri. Some astronomers have speculated that M22 may be the remnant core of a dwarf galaxy that was absorbed by the Milky Way long ago. For visual observers, M22 is among the easiest globular clusters to resolve. Even binoculars show a large, bright, granular ball of light, and a 4-inch telescope resolves stars across the cluster's face. Its southern declination means it never rises very high from northern locations, but from tropical and southern latitudes it is considered superior to M13.

Contains 70,000 to 83,000 stars within 99 light-years diameter at a distance of 10,600 light-years, shining at magnitude 5.1.