Charles Messier discovered M21 = NGC 6531 = h1993 on 5 Jun 1764. On 26 May 1786 (sweep 556), WH noted "a rich cluster of large stars." On 28 Jul 1830, JH recorded "A tolerably rich, sc, coarse cl; one star 9m, the rest 10....12." His single position was 6' too far east.

400/500mm - 17.5" (8/10/91): M21 consists of roughly 50 stars in a 5' diameter. Very bright, fairly small although outliers greatly increase the diameter. Includes a wide double star south 698 = 7.9/8.8 at 30". Just north of these stars is a remarkably symmetric ring consisting of a mag 9.5 star and ten mag 12-13 stars. A close mag 14/14 double star is on the west side of the bright double star. Just west is a 10' string of mag 8/9 stars oriented NW-SE including two double stars. M20 lies 45' SW. Easily visible in 15x50 IS binoculars as a small knot.

Notes by Steve Gottlieb