Messier 103 open cluster has been discovered by Pierre Mechain in 1781. Pierre was Charles Messier’s friend and collaborator, and Charles had no opportunity to verify this discovery before he presented his catalogue. M103 is one of the most distant open cluster known, which distances of 8,000 to 9,500 light years away. This open cluster contains over 150 member stars and it is pretty compact – its apparent size is 6 arc minutes. 

M103 nickname is “Christmas Tree Cluster” and it really looks like it. Interesting fact is, that the brightest star at the tree top does not belong to the cluster. It is Struve 131 – double start with two components separated by 13.9″ (7.3mag + 9.9mag). M103 is pretty young cluster, its age is estimated to about 25 million years. Most if its stars are hot, blue stars with apparent brightness 10-11mag, but there is impressive yellow-red bright star in the cluster centre, that breaks this rule.

Messier 103
M103 open cluster in Cassiopeia

Large version

Image was shot under suburban sky with Meade ACF 10″ telescope, QHY163M camera and EQ6 mount. It is LRGB composite 40:10:10:10 minutes, with 1 minute subframes. Transparency was quite decent this night, so color balance was not a problem, and stars look natural.

Clear skies!