NGC 6218

NGC 6218

Messier 12
Class IX[1]
Constellation Ophiuchus
Right ascension 16h 47m 14.18s[2]
Declination –01° 56′ 54.7″[2]
Distance 15.7 kly (4.8 kpc)[3]
Apparent magnitude (V) +7.68[4]
Apparent dimensions (V) 16′.0
Physical characteristics
Mass 8.7×104[5] M
Radius 37.2 ly[NB 1]
Metallicity –1.14[6] dex
Estimated age 12.67 Gyr[6]
Other designations NGC 6218[4]
See also: Globular cluster, List of globular clusters

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".[7] 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.[8] In a 10 in (25 cm) scope, the granular core shows a diameter of 3′ (arcminutes) surrounded by a 10′ halo of stars.[7]

Located roughly 3°[8] in the sky from the cluster M10 and 5.6° from the star Lambda Ophiuchi, M12 is about 15,700 light-years (4,800 parsecs)[3] from Earth and has a spatial diameter of about 75 light-years. The brightest stars of M12 are of 12th magnitude. 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.

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 the gravitational influence of the Milky Way.[9]

Notes

References

External links

  • Messier 12, SEDS Messier pages
  • Messier 12, Galactic Globular Clusters Database page
  • Messier 12 on Articles and images

, −01° 56′ 52.1″