M21 · open cluster

Messier 21

Messier 21 or M21, also designated NGC 6531 or Webb's Cross, is an open cluster of stars located to the north-east of Sagittarius in the night sky, close to the Messier objects M20 to M25.

RA18h 04m 13sDec−22° 29' 24"

Image: Wikimedia Commons. CC BY-SA 4.0, via Wikimedia Commons.

Identity & coordinates

Identification

Primary designation: M21
All designations: M21 · NGC 6531
Object type: Open Cluster
Constellation: Sagittarius
Best viewing: Summer

Coordinates & physical

Right ascension (J2000): 18h 04m 13s
Declination (J2000): −22° 29' 24"
Apparent magnitude (V): —
Distance: —

III

Visibility tonight

The science

Messier 21 or M21, also designated NGC 6531 or Webb's Cross, is an open cluster of stars located to the north-east of Sagittarius in the night sky, close to the Messier objects M20 to M25. It was discovered and catalogued by Charles Messier on June 5, 1764. This cluster is relatively young and tightly packed. 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. The cluster is positioned near the Trifid Nebula, but is not associated with that nebulosity. It forms part of the Sagittarius OB1 association.

Summary adapted from Wikipedia · CC-BY-SA-4.0