NGC 6540 is a globular cluster in the constellation Sagittarius. Its apparent magnitude is 9.3^[2] and its diameter is about 9.5 arcminutes, with 12 faint stars visible. It is about 17,000 light years away from Earth and was discovered by Wilhelm Herschel on May 24, 1784, with an 18.7-inch mirror telescope, who described the cluster as "pretty faint, not large, crookedly extended, easily resolvable".

NGC 6540
Image of NGC 6540 by the Hubble Space Telescope in August, 2022
Observation data (J2000 epoch)
Constellation	Sagittarius
Right ascension	18h 06m 08.60s[1]
Declination	−27° 45′ 55.0″[1]
Distance	17.3 kly (5.3 kpc)
Apparent magnitude (V)	9.30[2]
Physical characteristics
Absolute magnitude	-6.35[2]
Radius	4.75' x 4.75'[2]
Metallicity	${\displaystyle {\begin{smallmatrix}\left[{\ce {Fe}}/{\ce {H}}\right]\end{smallmatrix}}}$ = -1.35[3] dex
Other designations	Cr 364, Djorg 3, VDBH 258, C 1803-278[1]
See also: Globular cluster, List of globular clusters