Albert Marth discovered NGC 6820 = m 401 on 7 Aug 1864 and noted "F, S, R, bM." This number is usually associated with the large HII region Sh 2-86 = LBN 135, but Marth's position (and Bigourdan's measurements) point to IRAS 19403 +2258, a compact knot at 19 42 27.9 +23 05 15 (J2000).

200/250mm - 8" (10/4/80): Sh 2-86 extremely faint nebulosity in field of NGC 6823. Involves four stars in the north and two stars in the south side.

300/350mm - 13.1" (8/15/82): cluster NGC 6823 is encased in nebulosity (Sh 2-86) using a filter and averted vision. Very difficult to identify the nebulosity unfiltered.

400/500mm - 17.5" (8/10/91): at 100x using OIII filter, open cluster NGC 6823 is immersed in a faint nebulosity. Also extends 5'-10' SW from the core of the cluster to a group of stars that wasn't included in the description of NGC 6823.

The observation above refers to Sh 2-86, the usual identification of NGC 6820. But based on Marth's position and description, NGC 6820 more likely refers to a compact knot to the southwest of the cluster at this position. At 220x, it appeared as a small, 20" knot surrounding a faint stellar or quasi-stellar core. Interestingly, this object dimmed with OIII, UHC and H-beta, so it's likely a reflection nebula that is detached from the main mass of nebulosity to the northeast.

Notes by Steve Gottlieb