William Herschel discovered NGC 4173 = H II-372 = h1121 on 11 Apr 1785 (sweep 396). See description under NGC 4169. The RNGC misidentifies this galaxy as NGC 4170, which is nonexistent (possibly a star).

Although NGC 4173 appears perfectly lined up with NGC 4175, it is apparently in the foreground with a redshift only 1/3 of the other three galaxies.

300/350mm - 13.1" (4/12/86): very faint, very elongated NW-SE, low even surface brightness. Faintest in the NGC 4169 group = HCG 61 and located just 1.7' NNE of NGC 4169. Forms the north vertex of a rectangle with NGC 4174, and NGC 4175.

400/500mm - 18" (6/17/06): faint, fairly large, very elongated 4:1 NW-SE, 1.5'x0.4'. Overall, low surface brightness with a very weak central brightening. Faintest of the HCG 61 quartet though NGC 4173 lies in the foreground with a recessional velocity ionly 1/3 of the other members..

600/800mm - 24" (5/22/17): at 282x; fairly faint, very large, very elongated ~6:1 NW-SE with averted, 2.0'x0.35', low surface brightness. Only a broad weak concentration with no distinct core/nucleus.

900/1200mm - 48" (4/20/17): fairly faint to moderately bright, very large, edge-on 6:1 NW-SE, 2.5'x0.4', fairly low surface brightness with only a modest central brightening and no distinct core or nucleus.

Notes by Steve Gottlieb