William Herschel discovered NGC 5993 = H III-636 = h1937 on 18 Mar 1787 (sweep 718) and recorded "Two, that of which the place is taken [NGC 5993] vF, vS. In verifying it with 300 I perceived another sp [NGC 5992] still fainter, iF, vS, but rather larger than the former. DIstance about 1 1/2'."

400/500mm - 17.5" (5/10/91): fairly faint, fairly small, oval 3:2 NW-SE, broadly concentrated halo, substellar nucleus. Slightly brighter of a pair with NGC 5992 2.5' SSW.

Notes by Steve Gottlieb