- M 12 (NGC 6218)
M 12 is a bright globular cluster in the central region of the constellation Ophiuchus. It forms a nice pair with another globular cluster, M 10, located approximately 3 degrees south-east of it. The two clusters can easily be seen as adjacent small fuzzy balls of light in the field of 10 × 50 binoculars.
M 12 has a physical diameter of around 85 LY and lies at a distance of 20,780 LY. This makes it a bit smaller and a bit closer than M 10. With a visual magnitude of 6.8, it is too dim to be seen with the naked eye. M 12 has a mass equivalent to around 200,000 Suns. Like M 10, the orbit of M 12 keeps it in the inner halo of our galaxy. Currently, M 12 and M 10 are separated by about 5000 LY. It has been suggested that the two clusters may have been formed together and may still be influencing each other.
M 12 was first observed by Charles Messier on the 30th of May 1764, one night before discovering the nearby M 10. John Herschel described it as having "many stragglers in lines and branches extending some distance from the most condensed part", which is in contrast to M 10's more uniform appearance.
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