William Herschel discovered NGC 3158 = H II-639 = h678, along with NGC 3163, on 17 Mar 1787 (sweep 713) and noted "pB, cL, r." On 18 Mar 1831 (sweep 335), John Herschel logged, "B; R; psbM; 35 arc seconds."

200/250mm - 8" (3/28/81): faint, small, requires averted.

300/350mm - 13.1" (2/25/84): fairly bright, round, weakly concentrated, largest and brightest in a group.

400/500mm - 17.5" (3/23/85): fairly bright, irregular round or slightly elongated, small bright core. Brightest in the NGC 3158 group with NGC 3159 6.7' SSE, NGC 3160 4.7' N and NGC 3152 5.5' NW.

Notes by Steve Gottlieb