M12 Globular Star Cluster

Messier 12, also known as M12, is a globular cluster located in the constellation Ophiuchus. It was discovered by the French astronomer Charles Messier on May 30, 1764, who described it as a “nebula without stars.” Under dark conditions, this cluster can be faintly seen with a pair of binoculars, but resolving its individual stars requires a telescope with an aperture of at least 8 inches (20 cm). In a 10-inch (25 cm) telescope, the granular core appears to have a diameter of 3 arcminutes, surrounded by a halo of stars extending about 10 arcminutes.

M12 is located roughly 3 degrees northwest of the cluster M10 and 5.6 degrees east-southeast of the star Lambda Ophiuchi. It is also near the 6th magnitude star, 12 Ophiuchi. This cluster is approximately 16,400 light-years (about 5,000 parsecs) from Earth and has a spatial diameter of about 75 light-years. The brightest stars in M12 are of 12th magnitude. M10 and M12 are only a few thousand light-years apart, and each cluster would appear to have a magnitude of about 4.5 when viewed from the perspective of the other.

With a Shapley-Sawyer rating of IX, M12 is relatively loosely packed for a globular cluster and was once thought to be a tightly concentrated open cluster. Thirteen variable stars have been identified within this cluster. M12 is moving toward us at a velocity of 16 km/s.

A study published in 2006 concluded that M12 has an unusually low number of low-mass stars. The authors speculate that these stars may have been stripped from the cluster due to its passage through the relatively matter-rich plane of the Milky Way.