Albert Marth discovered NGC 6591 = m 372, along with NGC 6586, on 27 Jul 1864 and noted "eeF, vS, stell." His position is 3 seconds west and less than 1' south of PGC 61610 (separation 1.0'). HyperLEDA lists a total blue magnitude of 16.4 for PGC 61610, but this is certainly within the range of Lassell's 48-inch.

400/500mm - 17.5" (7/16/88): extremely faint, small, possibly elongated. A mag 15 star is at the south edge and a wide mag 13.5 pair is 1' NW. Located 6' ESE of NGC 6586 in the NGC 6579/80 group.

Notes by Steve Gottlieb