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Messier 21: Difference between revisions
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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. | 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 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. | ||
<ref>[http://en.wikipedia.org/wiki/Messier_21 Messier 21]</ref> | |||