William Herschel discovered NGC 5751 = H II-809 = h1877 on 24 Apr 1789 (sweep 927) and noted "F, S, E." His position is poor, but JH commented "vF; R; forms an obtuse-angled isosceles with 2 equal stars 10-11m, one p, one sf; dist of each 3'." and he measured a more accurate position (1' too far north).

400/500mm - 17.5" (6/18/93): fairly faint, fairly small, elongated 2:1 SW-NE, 1.2'x0.6, even surface brightness. Forms the vertex of an obtuse angle of 135° with two mag 11 stars 2.8' W and 3.1' SE of center.

Notes by Steve Gottlieb