Messier 10 or M10 (also designated NGC 6254) is a globular cluster in the constellation Ophiuchus. It has an apparent visual magnitude of 6.6 and its angular diameter is 15.1 arc-minutes. M10 lies at an estimated distance of 14,400 light years. The Equinox 2000 coordinates are RA= 16h 57.1m, Dec= -04° 06´ which makes M10 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 M10 through the Takahashi E-180 Astrograph (North is up). The bright star one degree east on M10 is 30 Ophiuchus (magnitude 4.80). A 2x enlargement of this image centered on M10 appears to the right.

This globular cluster was discovered by Messier in 1764. According to Recio-Blanco et al.(2005), the distance of M10 is 24,750 light years and its diameter is 140 light years. Its estimated mass is 200,000 solar masses and it contains 4 variable stars.

For more information, see the Messier Catalog as well as specific entries for M10 in Wikipedia and SEDS.

Messier's Description of M10

May 29, 1764
`Nebula, without stars, in the belt of Ophiuchus, near the 30th star of that constellation, of sixth magnitude, according to Flamsteed [30 Oph]. This nebula is beautiful and round; one can only see it with difficulty in an simple refractor of 3-feet. M. Messier has reported on the 2nd chart of the track of the Comet of 1769. Mem. Acad. for the year 1775, plate IX. Reviewed on March 6, 1781.' (Diam. 4')

[manuscript note in Messier's personal copy, 1780 catalog:] `Reviewed in the morning of March 6, 1781. "Always very fine."'

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