William Herschel discovered NGC 5990 = H II-425 = h1935 on 5 May 1785 (sweep 409) and logged "eF, vS, stellar. 240 confirmed it." JH made two observations, first describing it as "F; R; gbM; 20"."

Wolfgang Steinicke notes that NGC 5990 was observed on the last night of published observations at Birr Castle on 5 May 1878. Dreyer logged "pB, pS, gbM, * about 13m nf, dist 77", * possibly nebulous [perhaps referring to a very faint companion]."

400/500mm - 17.5" (6/11/88): moderately bright, fairly small, round, broad concentration, faint stellar nucleus, diffuse halo. A faint double is 3.5' ENE consisting of two mag 14.5 stars at 21" separation.

Notes by Steve Gottlieb