William Herschel discovered NGC 6451 = H VI-13 = h3707 on 24 Jun 1784 (sweep 232) and recorded "a cluster of small and pretty compressed stars of several magnitudes; about 5 or 6' in diam, not very rich." On 3 Aug 1834 (sweep 478), John Herschel logged "a remarkable cluster; divided into two by a broad, vacant, straight band; irreg R; 8' diam; st 12...15m. See fig 5, Pl V." His sketch shows two elongated groups of stars separated by a starless lane.
200/250mm - 8" (6/27/81): faint but rich group.
300/350mm - 13.1" (6/18/85): about three dozen stars in a 8' diameter. The brighter stars around the edges form the outline. Includes many very faint stars inside the bright border but unconcentrated towards the center.
Notes by Steve Gottlieb