Messier 21

Messier 21
Observation data (J2000.0 epoch)
Right ascension	18h 04.6m
Declination	−22° 30′
Distance	4.25 kly (1.3 kPc)
Apparent magnitude (V)	6.5
Apparent dimensions (V)	13.0′
Physical characteristics
Estimated age	4.6 million years
Other designations	NGC 6531
See also: Open cluster, List of open clusters

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.

External links

• Messier 21, SEDS Messier pages
• Messier 21 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images

Coordinates: 18^h 04^m 36^s, +22° 30′ 00″