Messier 21
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| Observation data: J2000.0 epoch | |
|---|---|
| Class: | I,3,m |
| Constellation: | |
| 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 | |
| Mass: | ( M☉) |
| Radius: | |
| VHB: | |
| Estimated age: | 4.6 million years |
| Notable features: | |
| Other designations: | NGC 6531 |
| See also: Open cluster, List of open clusters | |
Open Cluster M21 (also known as Messier Object 21 or NGC 6531) is an open cluster in the constellation 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 and contains about 57 stars.
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