M21 Open Cluster, AlBroxton

M21 Open Cluster

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Description

Messier 21 or M21 (also designated NGC 6531) is an open cluster of stars in the constellation of Sagittarius. It was discovered and catalogued by Charles Messier on June 5, 1764. M21 is a relatively young cluster of a mere 4.6 million years of age. It is tightly packed but contains about 57 stars. A few blue giant stars have been identified in the cluster, but Messier 21 is composed mainly of small dim stars. With a magnitude of 6.5, M21 is not visible to the naked eye; however, with the smallest binoculars it can be easily spotted on a dark night. M21 is an open cluster of about 40 stars varying in magnitude from 9 to 12. The cluster is located about 3,000 light-years from Earth and has a diameter of about 10 light-years. M21 has a total visual magnitude of about 6.5, which makes it an impressive sight in any small telescope. It can also be easily located with binoculars just a short distance from M20, the Trifid Nebula.

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M21 Open Cluster, AlBroxton