William Herschel discovered NGC 4657 = H I-177 = h1415 on 20 Mar 1787 (sweep 722). See descriptions under NGC 4656.

The UGC, MCG and CGCG list a single entry for the pair and NGC 4657 may be a tidally disturbed "tail" of NGC 4656 and not an independent galaxy. The primary designation for this object in NED is NGC 4656 NED02, with NGC 4657 the second identification. The position is on NE warped section (elongated E-W) of NGC 4656. The position is SIMBAD, though, is on the partially detached section close east with classification HII galaxy. HyperLeda has a listing for 2MASXJ12440844+3212340, with secondary designation NGC 4657 and object type "Part of galaxy". Corwin's position is on the brightest patch on the west side of E-W tail.

300/350mm - 13.1" (4/10/86): fairly faint, fairly small, elongated NNW-SSE. NGC 4657 is attached at the NE end of the remarkable galaxy NGC 4656 and elongated at nearly a right angle to the curving section of NGC 4656 just west.

400/500mm - 18" (5/14/07): The north end of NGC 4656 has a remarkable, fairly bright 2' extension (NGC 4657), hooking to the east at a 45° angle from the major axis (the "blade" of the hockey stick). There is a faint, small, detached knot beyond the east end of the "blade" that appears to have broken off. This unusual bend and knot is likely a starburst region of NGC 4656 and the result of a prior tidal interaction with its more massive neighbor, NGC 4631.

900/1200mm - 48" (4/23/17): NGC 4657 consists of at least 4 main HII complexes at the northeast end of NGC 4657, including a separate detached section. On the southwest edge is a bright knot, ~8" diameter, catalogued in SIMBAD as CasHII N4656f and in NED as NGC 4656:[DBT2008] 85 from a 2008 paper on massive clusters. A brighter 10" knot, identified in NED as 2MASX J12440599+3212340, is ~20" N, also along the west edge of the NE extension. The northeast end of the galaxy (NGC 4657) has a sharp extension to the east with a slightly brighter patch, identified in NED as 2MASX J12440844+3212340. Finally a bright, elongated patch ~30"x15" oriented NNW-SSE is detached to the east. SIMBAD identifies this object as NGC 4657, though the NGC designation should probably apply to the entire bent NE end of the galaxy.

Notes by Steve Gottlieb