M23 is an open star cluster in Sagittarius, discovered by Charles Messier in 1764. It has about 150 stars spread across a diameter of about 27 arcminutes and can sometimes be difficult to detect against the background Milky Way. The brightest stars are about 9th magnitude and about 50 stars are 12th magnitude or brighter. Its southerly declination means that it never reaches more than 18° above the horizon from the UK. This is easier than some of the more southern members of the Messier Catalogue but it still needs a clear night to get a good view with modest equipment. It is about 2,150 light years away and there is a foreground star of magnitude 6.9 that is not a member of the cluster.