Milwaukee Astronomical Society


M21 - NGC 6531 - Open Cluster


Messier 21 (M21) is a young Open Cluster of stars containing only about 57 confirmed members. This open cluster is located in the constellation Sagittarius. It is very close to M20, the Trifid Nebula (0.75 degrees) and is also near M8, the Lagoon Nebula (2.5 degrees). M21 can often be located in wide-field images of these two nebula. It is about 4,250 light years from earth and is approximately 20 light years in diameter. It was discovered by Charles Messier in 1764.

Location Data
Constellation: Sagittarius
Right ascension: 18h 4.6m
Declination: -22° 30′
Distance:  4,250 ly
Size:  20 ly

Observation Data
Apparent magnitude: 6.5
Apparent size: 13.0' arcmins

The images With Blue Borders were taken using equipment provided by the MAS Observatory
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