Messier 70, NGC 6681

Messier 70 (NGC 6681) is a globular cluster in Sagittarius, and one of the fainter and less conspicuous globulars in Messier's catalog.

Charles Messier discovered this globular in August, 1780, and described it as a "nebula without star." William Herschel was the first to resolve it into stars, and described it as "a miniature of M 3."

Due to its southern declination, M 70 is difficult to observe from the mid-northern latitudes where Messier discovered it. M 70 is the smallest and faintest of the three Messier globular clusters distributed along the base of the Teapot asterism, located about 2° northeast of M 69.

M 70 appears at visual magnitude 7.9, and about 8' in angular diameter. Its halo shows a fair number of stars against a granular background. The halo's edges are irregular; some of its brighter stars lie along short chains, the most conspicuous leading northeast away from the cluster. The globular's core is small and concentrated.

M 70 is at a distance of 29,300 light years from Earth, close to the Galactic Center, and is roughly 68 light years in linear diameter. Its absolute magnitude is -7.3, a luminosity of 70,000 Suns, and less than average for a globular cluster. This is roughly the same size and luminosity as M 69, its neighbor in space.

The core of M 70 is extremely dense, and has undergone a collapse sometime in its history, similar to other Milky Way globulars including M 15, M 30, and possibly M 62. Only two variable stars are known within M 70. It is receding from us rapidly, at about 200 km/sec.