William Herschel discovered NGC 4921 = H II-393 = h1516 on 11 Apr 1785 (sweep 396) and recorded "Three, the two following [NGC 4921 and 4923] pretty near each other; the south preceding [NGC 4911] about 8' distance; the time was near that of the two." JH made two observations and measured a fairly accurate position. d'Arrest made 6 observations.

300/350mm - 13.1" (5/14/83): fairly faint, fairly small, round, 3rd of 3 in AGC 1656.

400/500mm - 17.5" (4/21/90): fairly faint, fairly small, bright core, large low surface brightness halo surrounded core. This is one of the brighter members of AGC 1656 but it appears fainter than the integrated V magnitude suggests. Nearby are NGC 4923 2.7' SSE and NGC 4919 5.1' SSW.

Notes by Steve Gottlieb