With a visual magnitude of 5.5, M22 is the brightest globular cluster visible from the mid-northern latitudes. However, as it lies in the southern constellation Sagittarius, M22 never rises very high in the sky and can’t really be observed in all its glory from the northern hemisphere. Messier 22 is one of only four globular clusters that contain a planetary nebula. M22 is also one of the nearest globulars to the solar system. The only globular cluster closer to Earth is Messier 4, located in the neighboring constellation Scorpius. M22 is elliptical in shape.
|Visible From Pacific Northwest||May, June, July, and August|
|Best Time To Observe||August|
|Minimum Size Of Viewing Device||Binoculars|
|Object Type||Globular Cluster|
|Designations||Messier 22, M22, NGC 6656, GCl 99, C 1833-239, MWSC 2961, Lacaille I.12|
|Right Ascension||18h 36m 23.94s|
|Number Of Stars||83,000|
|Object Radius||50 light years|
|Distance From Earth||10,600 light years|
Messier 22 was discovered by Abraham Ihle, a German amateur astronomer, on August 26, 1665. Ihle stumbled upon the cluster while observing Saturn. M22 is probably the first globular cluster to have been discovered. As it lies very close to the ecliptic, planets often come very close to it, which is how Ihle discovered it.
Messier 22 would latter be 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. Then Halton Arp and William G. Melbourne continued studies in 1959. 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.
Locating M22 In The Sky
The most important clue is simply identifying the Sagittarius “teapot” shape. Once you’ve located it, just choose the “lid” star, Lambda (Kaus Borealis) and look about a fingerwidth (2 degrees) due northeast.
Visible to the naked eye in good conditions, the cluster lies only 2.5 degrees to the northeast of Kaus Borealis, the star that marks the top of the Teapot in Sagittarius. In binoculars, M22 appears as a faint patch of light. Small telescopes will resolve the brightest stars and larger instruments will reveal stars across the cluster.
Messier 22, the Sagittarius Cluster is not one of the most popular stars to photography; therefore, finding tips and tricks will be rather tough. What can be found might not necessarily be helpful, but what is required is precision guidance to make sure that the stars are crisp. Moreover, this article has a good guide for potential options for your setup and configuration of 20 light frames and, 10 dark frames.
Sources And Further Reading
Descriptions of all of Messier Objects can be found here.