Heinrich d'Arrest discovered NGC 4821 on 6 Apr 1864 with the 11-inch refractor at Copenhagen while observing and measuring nearby NGC 4819. His position is fairly accurate.

400/500mm - 17.5" (5/14/94): fainter and smaller of pair with NGC 4819 2.0' N. Faint, small, slightly elongated 4:3 N-S, no concentration. A mag 14.5 star is 1.5' WSW and a mag 13.5 is 3.5' W (this star forms the western vertex of an isosceles triangle with NGC 4821 and NGC 4819). NGC 4827 lies 13.8' N. Outlying member of AGC 1656.

Notes by Steve Gottlieb