Originally listed as an open cluster, this object was reclassified as a globular in 1987 by Djorgovski.

William Herschel discovered NGC 6540 = H II-198 on 24 May 1784 (end of sweep 224) and recorded "pF, crookedly extended easily resolvable nebula; or rather a cluster of very close stars; not large."

Guillaume Bigourdan's description mentions a size of 1.5' x 25", elongated E-W, stars mag 13 and fainter containing possible "nebulous material". So, Bigourdan was clearly describing the entire string of stars.

300/350mm - 13.1" (9/3/83): very faint, small, rich spot, slightly elongated E-W, mottled but no resolved. Also a group of six faint stars in an arc to the SE. Dark nebula B86 lies 41' W.

400/500mm - 17.5" (7/10/99): this interesting globular is located nearly midway along a short 1.5' E-W arc of a half dozen or so mag 13-14 stars that are bowed out to the north. The globular is a faint, round, 40" glow, embedded just inside the center of this string which extends beyond the globular to the west and east. At 100x, this string, along with the haze of the cluster creates the impression the globular is quite elongated.

Notes by Steve Gottlieb