William Herschel discovered NGC 5566 = H I-144 = h1779, along with NGC 5560, on 30 Apr 1786 (sweep 558) and noted "cB, cL, R, gmbM." JH made 3 observations and recorded (sweep 426) "B; R; 40"; gbM; r; has a *12m 1 diam of neb dist nf."

400/500mm - 17.5" (3/23/85): bright, fairly small, slightly elongated SSW-NNE, small bright nucleus. Brightest of three with NGC 5560 5.3' NW and NGC 5569 4.1' NE. A mag 12 star is 1.6' E of center. A pair of mag 8 and 9 stars (SAO 120402 and 120403) lie 10' NW. NGC 5576 (brightest in a trio) lies 40' SSE.

600/800mm - 24" (5/11/13): very bright, very large, very elongated 3:1 SW-NE. Very sharply concentrated with a large, bright elongated core that is also sharply concentrated with an intense elongated nucleus, angled with respect to the major axis. The halo is very diffuse without a sharp edge, but extends at least 4.0'x1.3'. The core is bracketed by mag 12 and 14 stars to the east and west, respectively. NGC 5569 lies 4.3' NE, beyond the edge of the galaxy, and NGC 5560 is 5.3' NW.

900/1200mm - 48" (5/4/16): at 375x; extremely bright and large, very elongated 4:1 SW-NE, 6.0'x1.5'. Very sharply concentrated with a large, roundish, very bright core containing a large, very intense nucleus! The southern extension or arms is slightly wider than the northern counterpart and more evenly lit, though it is brighter along its southern edge, particularly closer to the core region (this is the edge of a spiral arm). The northern branch is brighter along its northern edge and appears to be a low contrast spiral arm, bending or twisting slightly counterclockwise (towards the east). A mag 12 star is 1.6' E of center and a mag 13.8 star is 1.2' WSW. Brightest in an excellent trio with NGC 5560 5.3' NW and NGC 5569 4.3' NE.

Notes by Steve Gottlieb