William Herschel discovered NGC 3550 = H III-351 = h829, along with NGC 3552, on 11 Apr 1785 (sweep 396). He recorded "Two [along with III-352 = NGC 3552], both vF and vS. The most south NGC 3552] is the faintest and but for the other could not have been observed." John Herschel made 6 disparate descriptions in terms of brightness - ranging from eF to B - and in the notes to the General Catalogue suggested this was possibly a variable nebula.

300/350mm - 13.1" (3/24/84): brightest in the AGC 1185 cluster. Faint, small, round. A mag 11 star is 1.5' E and a mag 12 star 1.5' SSW. NGC 3552 lies 4.7' SSE.

Notes by Steve Gottlieb