William Herschel discovered NGC 5491 = H II-890 = h1753 on 12 May 1793 (sweep 1043) and recorded "pB, pS, iR." CH's reduced position is 2.5' southwest of UGC 9072. JH made 4 observations and recorded (sweep 154), "pF; pL; gbM; 25"." d'Arrest made an additional 3 observations and measured an accurate position.

400/500mm - 17.5" (5/10/91): fairly faint, fairly small, oval 3:2 WSW-ENE, elongated bright core. Bracketed between two mag 15 stars 30" off the ENE edge and 1' WSW. Forms an interacting pair with NGC 5491B at the north edge of halo (not seen).

600/800mm - 24" (6/15/15): moderately bright, fairly small elongated 4:3 WSW-ENE, 40"x30", contains a small bright core. Forms a close pair with NGC 5491B at the north edge of the halo, just 25" from the center. At 375x (6mm ZAO) this compact companion appeared very faint, nearly stellar, visible ~1/3 of the time. A mag 14.8 star is 0.9' NE and a second mag 15 star (misclassified by Holmberg as 597c) is 1.0' SW. Double star BRT 2158 = 12.5/12.7 at 4.5" lies 2.7' NE.

Notes by Steve Gottlieb