Lewis Swift discovered IC 646 = Sw. IX-25 on 8 May 1890 and recorded "eeF; pS; R; nf of 2 [with IC 644 = NGC 3398]." Swift's RA is 12 seconds too large. PGC and RC3 (as well as Megastar) misidentify IC 646 as NGC 3398. See NGC 3398 for more.

400/500mm - 17.5" (4/22/95): very faint, small, slightly elongated NW-SE, 0.5'x0.4'. Forms a pair with brighter NGC 3398 4.6' SSW.

Notes by Steve Gottlieb