Heinrich d'Arrest discovered NGC 503 on 13 Aug 1863 with the 11-inch refractor at Copenhagen. His single micrometric position is an exact match with CGCG 502-065 = PGC 5086. He was uncertain if it might be one of William Herschel's previous discoveries in the area [NGC 495, 496 and 499].

400/500mm - 17.5" (10/4/97): very faint, very small, round, 20" diameter. Collinear with two mag 13.5 stars 0.6' SE and 1.0' SE. Located 4' NE of mag 7.5 SAO 54647 within the NGC 507 Group NGC 507/508 in the field).

600/800mm - 24" (10/4/13): fairly faint, very small, slightly elongated, 20"x15". Two mag 13.4/13.8 stars 0.6' SE and 1.1' SE are collinear with the galaxy. Located 4' NE of mag 7.6 HD 8347 and 5' NNW of NGC 507, in the central hub of the cluster.

Notes by Steve Gottlieb