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M 103 is a small open cluster visible in the central part of the Cassiopeia constellation.
It is one of the furthest open clusters listed in the Catalog of Messier, lying at about 2880 parsecs (9400 light years) from the Earth, in a remote corner of the Arm of Perseus.
It has an apparent diameter of 6 arc minutes which, considering the distance, corresponds to a real diameter of 15 light years.