NGC 6522

NGC 6522
32 inch telescope NGC 6528 (lower left) and NGC 6522 (upper right)
Observation data (J2000 epoch)
Constellation	Sagittarius
Right ascension	18h 3m 34.1s
Declination	−30° 2′ 2.3″
Distance	25.1 kly (7.7 kpc)
Apparent magnitude (V)	10.5
Apparent dimensions (V)	2'
Physical characteristics
Mass	7005300000000000000♠3.00×105 M☉
Metallicity	${\displaystyle {\begin{smallmatrix}\left[{\ce {Fe}}/{\ce {H}}\right]\end{smallmatrix}}}$ = –1.34dex
Estimated age	12.0 Gyr
See also: Globular cluster, List of globular clusters

NGC 6522 is a globular cluster in the constellation Sagittarius. It is apparent magnitude 10.5, and diameter 2 arc seconds, and class VI with stars 16th magnitude and dimmer. It was discovered by William Herschel on June 24, 1784. It is centered in a region of the sky known as Baade's Window.

NGC 6522 is possibly the oldest star cluster in the Milky Way, with an age of more than 12 billion years.