Messier 103 M103 NGC 581, Cassiopeia
Messier 103 is a small cluster in Cassiopeia, discovered by Mechien in the spring of 1781, and included by Messier, without confirmation, as the last entry in his catalog. The remaining catalog entries, 104 to 110, were added in the 20th century. The brightest star in the cluster is a 7.3 magnitude multiple star system, Struve 131, or HD 9311, which is actually not a member, but a nearby foreground object. The cluster itself contains 172 confirmed members, including a magnitude 8.2 blue supergiant, and a magnitude 8.5 red giant. M103 is one of the smallest and most distant open clusters known. Its apparent magnitude is 7.4, and angular size only 6 arcmin. It is estimated to be 25 million years old, to have a diameter of 17.5 light years, to lie at the distance of 10,000 light years, and to be approaching us at about 40 km/sec.
The attached photo was taken last year with a TSapo100q astrograph, Sigma 1.4x apo tele-extender, Canon 600D camera, IEQ30pro mount, and Orion 60mm f/4 SSAGpro autoguider. The image is a 25% crop of a stack of 9x300 second exposures at ISO 1600, no filters, processed with 2x drizzle and 30 dark and 30 bias frame masters. Software used was PHD2, DSS, XnView, StarTools, and Neat Image. Compared to the DSS2 sky survey, limiting magnitude on the original image is 17.5.
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