M21 (NGC 6531)
Messier M21 (NGC 6531) is a open cluster located in the constellation Sagittarius, in the Sagittarius Arm of the Milky Way Galaxy. in the Local Group of galaxies.
Messier M21 is best viewed during late summer, is magnitude 7.0*, and can be viewed with binoculars. It is 13' in size. For reference, the full moon is 30' (arc minutes) in size.
* The naked eye can see up to magnitude 8 objects under ideal dark sky conditions.
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