William Herschel discovered NGC 4559 = H I-92 = h1352 on 11 Apr 1785 (sweep 396) and recorded "eB, vL, beautiful. Four stars are scattered over it. pmE from np to sf. The greatest brightness is not in the middle but more towards the following part, where 3 of the 4 stars are placed; the whole extent may be 10 or 12'. JH made 3 observations and logged "vL; gbM, but not to a nucleus; mE; has 3 stars south following. By a diagram, the southern end is broader than the norther, giving it a clubbed appeared."

IC 3550-52, IC 3555, and IC 3563 are HII regions and/or star clouds within NGC 4559 that were discovered photographically by Max Wolf on a Heidelberg plate.

400/500mm - 17.5" (4/9/99): bright, large, elongated 5:3 NW-SE, ~7'x3'. Exhibits a striking, unusual appearance with a broad, weak concentration to a large, elongated core. The overall surface brightness is noticeably irregular with hints of brighter and darker spots. The outer halo has a low surface brightness, particularly on the SE end which is wider than the NW side and shows no tapering. A trio of mag 12-12.5 stars cradle the galaxy at this end and there appears to be mottling near the superimposed stars. NGC 4559 is located exactly 2.0° N of NGC 4565.

900/1200mm - 48" (4/7/13): very bright, very large, very elongated 3:1 NW-SE, 9'x3', large bright core that gradually increased to the center. The core appeared irregular, mottled and dusty. The inner portion of the disc showed weak spiral structure. At 488x, the outer halo was very patchy with several knots. Superimposed on the southeast side are three mag 12/12.5/13 stars between 1.5'-2' from center and the galaxy faded out rapidly beyond these stars to the southeast. Near the southeast end is IC 3563, a very compact HII region and IC 3564, a star association attached on the east side. Both objects were easily visible but merged as a fairly faint 20" patch, 3' SE of center.

The outer halo faded out gradually and extended much further on the northwest side, up to 5' NW of center. IC 3555 is faint, 20"x10" HII region, extended NW-SE, and situated 1.8' NNW of center in the halo. IC 3552, a smaller HII region close NW, was not seen. IC 3551 seen as a faint, 10" HII knot on the west edge, 0.9' WNW of center. IC 3554 is a mag 15 star 2.1' SSW of center (at the edge of the visible disc) and IC 3550 = NGC 4559C was seen as a faint, 8" HII knot 0.8' WNW of the star. All of the IC numbers were found by Max Wolf on a Heidelberg plate in 1903.

Notes by Steve Gottlieb