William Herschel discovered NGC 3998 = H I-229 = h1031 on 14 Apr 1789 (sweep 920), along with NGC 3990, and recorded both as "Two, the last [NGC 3998] cB or vB, R, vgbM. The preceding NGC 3990] pB, E, S." His offset from NGC 3990 (22 sec of RA) is accurate.

400/500mm - 17.5" (4/6/91): very bright, fairly small, slightly elongated 4:3 NW-SE, sharply concentrated with a round very bright well-defined core, increases to stellar nucleus. Located 5.6' SSE of mag 9.2 SAO 28204. Forms a pair with NGC 3990 3.0' W. Brightest in a group including NGC 3982, NGC 3972 and NGC 3977.

Notes by Steve Gottlieb