Messier 12

Messier 12
Messier 12
	Globular cluster Messier 12 in Ophiuchus
Observation data (J2000 epoch)
Class	IX
Constellation	Ophiuchus
Right ascension	16h 47m 14.18s
Declination	–01° 56′ 54.7″
Distance	16.44 ± 0.16 kly (5.04 ± 0.05 kpc)
Apparent magnitude (V)	6.7
Apparent dimensions (V)	16.0′
Physical characteristics
Mass	8.7×104 M☉
Radius	37.2 ly
Metallicity	= –1.14 dex
Estimated age	13.8 ± 1.1 Gyr
Other designations	NGC 6218
	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".^[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]

Messier 12 core by HST
The Central Part of Messier 12. Credit: ESO
Map showing the location of M12

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^ "Messier 12". SEDS Messier Catalog. Archived from the original on 1 July 2022. Retrieved 27 April 2022.
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^ "Messier 12: Gumball Globular | Messier Objects". www.messier-objects.com. 11 March 2015. Retrieved 2015-08-17.
^ Cite error: The named reference eso2006 was invoked but never defined (see the help page).

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[4] "Messier 12". SEDS Messier Catalog. Archived from the original on 1 July 2022. Retrieved 27 April 2022.

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[12] "Messier 12: Gumball Globular | Messier Objects". www.messier-objects.com. 11 March 2015. Retrieved 2015-08-17.

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