M6 - Butterfly Cluster

Messier 6 or M6 (also designated NGC 6405) is an open cluster in the constellation Scorpius. It has an apparent visual magnitude of 4.2 and its angular diameter is 25 arc-minutes. M6 lies at an estimated distance of 1600 light years. The Equinox 2000 coordinates are RA= 17h 40.1m, Dec= -32° 13´ which makes M6 best seen during the summer. The Messier Summer Star Chart shows the position of all Messier objects visible during that season. As one of the more famous objects in the Messier Catalog, it is commonly known as the Butterfly Cluster.

The image above shows the uncropped view of M6 through the Takahashi E-180 Astrograph (North is up). A 2x enlargement of this image appears to the right.

In spite of its inclusion in the Messier Catalog, this open cluster was actually discovered by G. B. Hodierna in 1654. According to Kharchenko et al. (2005), the distance of M6 is 1590 light years and its diameter is 10 light years. It contains 64 stars and its estimated age is 80-100 million years.

For more information, see the Messier Catalog as well as specific entries for M6 in Wikipedia and SEDS.

Messier's Description of M6

May 23, 1764
`Cluster of small stars between the bow of Sagittarius and the tail of Scorpius. At simple view [to the naked eye], this cluster seems to form a nebula without stars; but even with the smallest instrument one employs for investigating one sees a cluster of small [faint] stars. (Diam. 15')'

Technical Details

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