Celestial hemisphere:  Southern  ·  Constellation: Ophiuchus (Oph)  ·  Contains:  M 12  ·  NGC 6218
Messier 12 or M12, Stephen Harris
Messier 12 or M12
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Messier 12 or M12

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Description

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". 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.

Located roughly 3° 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, 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.

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Messier 12 or M12, Stephen Harris