William Herschel discovered NGC 3997 = H III-324 = h1033, along with NGC 3987 = H III-323, on 6 Apr 1785 (sweep 393) and recorded "vF, lE. Suspected another eF, about 5' or 6' nef. I was pretty sure of it." NGC 3997 is 7.8' NE of NGC 3987, while NGC 3993 is 4.7' NE, so either could apply but NGC 3997 is slightly brighter. JH measured an accurate position and described "F; vS; E pos 25° Between 2 stars, 80" dist."

The two WH numbers have been applied to different galaxies. JH equated NGC 3997 = H III-323 in the Slough catalogue. Dreyer gave a possible equivalence of NGC 4015 = H III-323 and NGC 4021 = H III-324 in the NGC, which in the 1912 "Scientific Papers of WH", Dreyer equates NGC 3987 = H III-323 and NGC 3993 = H III-324.

400/500mm - 17.5" (3/19/88): faint, small, elongated ~E-W (central bar), small bright core. Bracketed by two mag 12 stars 0.9' E and 0.9' SW of center. Member of the NGC 4007 group.

600/800mm - 24" (3/22/14): moderately bright to fairly bright, moderately large, irregular, ~1.0'x0.7'. Contains a small brighter core embedded in a curving bar oriented ~E-W. There was an impression of weak spiral arms in the halo. Bracketed by two mag 12.5-13 stars just off the east and southwest side. Brightest and fourth in a string with NGC 3993 3' SW and NGC 3987 7.7' SW.

Notes by Steve Gottlieb