M12
NGC 6218
Properties
Position & Identifiers
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M12 · 11.1′ diameter · N up, E left
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About M12
Description
M12 is a loose, bright globular cluster in Ophiuchus, about 15,700 light-years from Earth. It is similar to its neighbor M10 but noticeably less concentrated, giving it a more open, airy appearance. The cluster spans about 75 light-years and contains several hundred thousand stars.
Observing Tips
Located about 3.4 degrees northwest of M10 — the two fit in the same binocular field and make a wonderful comparison pair. A 4-inch telescope at 80-100x shows a large, bright, somewhat loose globular with a granular texture. An 8-inch telescope resolves stars easily across the entire cluster due to its low concentration. Note how much more spread out M12 appears compared to M10. Best observed from June through August.
History
Discovered by Charles Messier on May 30, 1764. He described it as a 'nebula without stars.' William Herschel resolved it into individual stars in 1784 and noted its loose structure.
Fun Facts
M12 has lost a disproportionate number of low-mass stars compared to other globulars. Studies suggest the Milky Way's tidal forces have stripped away about one million low-mass stars over the cluster's lifetime, leaving it with an unusual ratio of heavier to lighter stars. It was once classified as a very dense open cluster before being confirmed as a true globular.