Messier 12 or M12 (also designated NGC 6218) is a globular cluster in the constellation Ophiuchus. It has an apparent visual magnitude of 6.7 and its angular diameter is 14.5 arc-minutes. M12 lies at an estimated distance of 16,000 light years. The Equinox 2000 coordinates are RA= 16h 47.2m, Dec= -01° 57´ which makes M12 best seen during the summer. The Messier Summer Star Chart shows the position of all Messier objects visible during that season.

The image above shows the uncropped view of M12 through the Takahashi E-180 Astrograph (North is up). A 3x enlargement of this image appears to the right.

This globular cluster was discovered by Messier in 1764. According to Recio-Blanco et al.(2005), the distance of M12 is 20,760 light years and its diameter is 85 light years. Its estimated mass is 250,000 solar masses and it contains 5 variable stars.

For more information, see the Messier Catalog as well as specific entries for M12 in Wikipedia and SEDS.

Messier's Description of M12

May 30, 1764
`Nebula discovered in the Serpent, between the arm and the left side of Ophiuchus: this nebula doesn't contain any star, it is round and its light faint; near this nebula there is a star of 9th magnitude. M. Messier has reported it on the second Chart of the Comet observed in 1769. Mem. Acad. 1775, pl. IX. Reviewed March 6, 1781. (diam. 3')'

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