Messier 103 or M103 (also designated NGC 581) is an open cluster in the constellation Cassiopeia. It has an apparent visual magnitude of 7.4 and its angular diameter is 6 arc-minutes. M103 lies at an estimated distance of 8500 light years. The Equinox 2000 coordinates are RA= 1h 33.2m, Dec= +60° 42´ which makes M103 best seen during the autumn. The Messier Autumn Star Chart shows the position of all Messier objects visible during that season.

The image above shows the uncropped view of M103 through the Takahashi E-180 Astrograph (North is to right). A 3x enlargement of this image appears to the right.

This loose open cluster was discovered by P. Méchain in 1781. It is one of the more distance open clusters in the Messier Catalog. According to Kharchenko et al. (2005), the distance of M103 is 7150 light years and its diameter is 17 light years. It contains 77 stars and its estimated age is 16-25 million years.

For more information, see the Messier Catalog as well as specific entries for M103 in Wikipedia and SEDS.

Messier's Description of M103

Méchain) `Cluster of stars between Epsilon and Delta of the leg of Cassiopeia.'

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