Heinrich d'Arrest discovered NGC 4121 on 9 Sep 1866 with the 11-inch refractor at Copenhagen. His position, measured on 3 nights, matches CGCG 315-018 = PGC 38508.

400/500mm - 17.5" (3/20/93): fairly faint but very small, round, stellar nucleus surrounded by a small round halo. Forms a pair with bright galaxy NGC 4125 3.6' NE.

Notes by Steve Gottlieb