M103

M103 (Ngc581) is one of the more remote open clusters in Messier's catalog, at about 8,000 light years distant in one of the most recognised constellations of Cassiopeia the queen. Visible in my binoculars against a rich star field it was the last entry to his original catalogue without him actually observing it. Well Mr Messier I have seen it. and I have ticked it off my list. The bright star also visible at the top is Ruchbah or(δ) Delta Cassiopeiae  Cassiopeiae. See finder chart. To me this star is a little more interesting than the cluster. It is an eclipsing binary star system consisting of a pair of stars that orbit about each other over a period of 759 days.


The primary a white sub giant has a stellar classification of A5III-IV, with the luminosity class of IV indicating that it has exhausted the hydrogen at its core and has begun to evolve through the subgiant phase into a giant star. It has expanded to about 3.9 times the Sun's radius. It is moving through the Galaxy at a speed of 43.9 km/s relative to the Sun.