M23 (NGC 6494)
Messier 23 (NGC 6494) is an open cluster located in the constellation Sagittarius, in the Orion Arm of the Milky Way Galaxy in the Local Group of galaxies. M23 is 21,000 light years away from Earth.
M23 is best viewed during late summer, is magnitude 5.5, and can be viewed with naked eye (barely). M23 is 35' in apparent 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.