William Herschel discovered NGC 5645 = H II-150 = h1823 on 13 Apr 1784 (sweep 192) and recorded "F, pS, nearly R, easily resolvable." His position (CH's reduction) is 3.5' north of UGC 9328. He made another observation on 12 May 1793 (sweep 1042), logged "cB, iF, about 2' long and 1 1/2' broad" and measured an accurate position. John Herschel made two observations, describing it as both "vF" (on 8 May 1828) and "pB" (on 19 Apr 1830).

200/250mm - 8" (6/29/84): faint, small, diffuse, low surface brightness, irregularly round, slightly elongated ~E-W. A mag 10 star is ESE. Located near the Bootes border.

400/500mm - 17.5" (6/8/91): fairly faint, fairly small, 2.0'x1.5', elongated 3:2 E-W, gradually increases to elongated ill-defined core. Located 6' W of mag 9.1 SAO 120507.

Notes by Steve Gottlieb