Messier Object 12 (original) (raw)

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Globular ClusterM12 (NGC 6218), class IX, in Ophiuchus

[ ](../Jpg/m12.jpg)

Discovered by Charles Messier in 1764.

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.

Helen Sawyer Hogg determined the cluster's overall spectral type as F7 and gives its color index as 0.0, and the mean magnitude of the 25 brightest stars as 13.97. The brightest stars of M12 are about mag 12.0, its horizontal branch level (of giant stars) is magnitude 14.9, according to the Deep Sky Field Guide to Uranometria 2000.0. Alan Sandage has found 13 variables in M12.

M12 is one of Charles Messier's original discoveries, found on May 30, 1764. Like many other globular clusters, Messier described it as "Nebula without stars", as did Bode 10 years later; a consequence of the modest resolving power of their instruments. William Herschel was the first to resolve it into stars in 1783.

Globular cluster M12 is easily found either 2 deg N and 2 deg W of M10, or 2 deg N and 8.5 deg E from Delta Ophiuchi.

• Historical Observations and Descriptions of M12
• ESO/VLT images of M12
• More images of M12
• Amateur images of M12
• Marco Castellani's data for M 12
• Christine Clement's Catalog of Variable Stars in M12
• Holger Baumgardt's Fundamental Data for M12 (NGC 6218)
• SIMBAD Data of M12
• NED Data of M12
• Publications on M12 (NASA ADS)
• Observing Reports for M12 (IAAC Netastrocatalog)
• NGC Online data for M12

Hartmut Frommert
Christine Kronberg
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Last Modification: August 21, 2007