William Herschel discovered NGC 5576 = H I-146 = h1783 on 30 Apr 1786 (sweep 558), along with NGC 5574, and recorded "Two; the preceding NGC 5574], pB; pL; E. Distance 3' or 4' sp nf." On a later sweep he noted I-146 was "cB, R, pL." JH recorded "vB; R; vsmbM; a star 11 mag north-preceding and the nebula I 145 NGC 5574] south-preceding makes a right-angled triangle with I 146 at the right angle."

400/500mm - 17.5" (3/23/85): fairly bright, bright core, bright stellar nucleus. A mag 13 star is at the NW edge 1.3' from center. Brightest of three with NGC 5574 2.7' SW and NGC 5577 10.2' NNE.

600/800mm - 24" (6/8/13): very bright, fairly large, slightly elongated E-W, 2.0'x1.6'. Well concentrated with a large, very bright core and a more diffuse halo that gradually fades out. The core gradually increases to the center. A mag 13 star is 1.2' NW of center at the NW edge. Brighter of a striking pair with NGC 5574 2.8' SW.

Notes by Steve Gottlieb