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Globular Cluster in the Constellation Ophiuchus
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Messier 12 (M12, NGC 6218) is nearly a twin of its apparent neighbor, M10, and is only slightly larger and an idea fainter. Nevertheless, it was once believed to be an intermediate type between globular and dense open clusters (like M11), as it is not very concentrated - Harlow Shapley included M12 in his concentration class IX. It is, e.g., notably much less concentrated toward the center than M10 (of class VII). At its distance of about 16,000 light years, the apparent diameter of M12 of 16.0 arc minutes corresponds to about 75 light years. This stellar swarm is approaching us at 16 km/sec.
Text Credit: SEDS
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