Messier 10, NGC 6254

Messier 10 (NGC 6254) is one of the bright globulars populating the constellation Ophiuchus. It was discovered by Charles Messier in 1764, who described it as a "nebula without stars". Although they are plainly visible in a modern 4-inch telescope, William Herschel was the first to resolve M 10 into stars.

Messier 10 is a very rich globular cluster, located in the rather barren central region of Ophiuchus, near ε Oph. At magnitude 6.5, it is one of the better globulars in the sky. M 10 has an apparent diameter of some 20', about 2/3 the apparent diameter of the Moon. At an estimated distance of 14,300 light-years, this translates to a physical diameter of 83 light-years. Viewed through medium-sized telescopes, it appears about half that size (8' to 9'), as its bright core is only 35 light-years across. Four variable stars have been discovered in M 10.

M 10 is receding from us at 69 km/sec. The cluster completes an orbit through the Milky Way galaxy about every 140 million years, during which it crosses the plane of the galactic disk every 53 million years. This orbit has an eccentricity of e=0.21.