Deep space
Webb's Cross Cluster
Open cluster · M21 · NGC 6531
Open cluster in Sagittarius
Photo: Wikimedia Commons · Public domain · Wikimedia Commons
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.
Description from Wikipedia (CC BY-SA 4.0).
In your sky
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Key facts
Distance
~4,250 light-years
Apparent mag.
+6.5
Apparent size
14′
Best seen with
Naked eye (dark sky)
Catalogue
M21 · NGC 6531
Did you know
- Listed as Messier 21 in the Messier catalogue, also known as NGC 6531.
- Found in the constellation Sagittarius.
- Visible to the naked eye from a dark, moonless site.
