History[edit]
M22 was one of the first globulars to be discovered, on August 26, 1665 by Abraham Ihle[3] and it was included in Charles Messier's catalog of comet-like objects on June 5, 1764.
It was one of the first globular clusters to be carefully studied first by Harlow Shapley in 1930. He discovered roughly 70,000 stars and found it had a dense core.[10] Then Halton Arp and William G. Melbourne continued studies in 1959.[11] Because of the large color spread of its red giant branch (RGB) sequence, which is similar to that observed in Omega Centauri, it became the object of intense scrutiny starting in 1977 with James E. Hesser et al.[3][12]