From Wikipedia:
Messier 12 or
M 12 (also designated
NGC 6218) is a
globular cluster in the
constellation of
Ophiuchus. It was discovered by the French astronomer
Charles Messier on May 30, 1764, who described it as a "nebula without stars".
[8] In dark conditions this cluster can be faintly seen with a pair of binoculars. Resolving the stellar components requires a telescope with an
aperture of 8 in (20 cm) or greater.
[9] In a 10 in (25 cm) scope, the granular core shows a diameter of 3′ (
arcminutes) surrounded by a 10′ halo of stars.
[8]M12 is roughly 3°
[9] northwest from the cluster
M10 and 5.6°
east southeast from star
Lambda Ophiuchi. It is also located near the 6th magnitude
12 Ophiuchi.
[10] The cluster is about 16,400 light-years (5,000 parsecs)
[3] from
Earth and has a spatial diameter of about 75 light-years. The brightest stars of M12 are of 12th
magnitude. M10 and M12 are only a few thousand light-years away from each other and each cluster would appear at about magnitude 4.5 from the other.
[10] With a Shapley-Sawyer rating of IX,
[1] it is rather loosely packed for a globular and was once thought to be a tightly concentrated
open cluster. Thirteen
variable stars have been recorded in this cluster. M12 is approaching us at a velocity of 16 km/s.
[11]A study published in 2006 concluded that this cluster has an unusually low number of low-mass stars. The authors surmise that they were stripped from the cluster by passage through the relatively matter-rich plane of the
Milky Way.
[12]
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