M-103 (NGC-581) is a bright open star cluster located in the constellation of Cassiopiea, about 1 degree east of Delta Cassiopieae, on a line between Delta and Epsilon Cassiopieae. It lies approximately 10,000 light years from Earth and is 18 light years in diameter. The cluster is dominated by the 7.5 magnitude multiple star Struve 131, which is not an actual member of the cluster and lies much closer to us, but in the same line of sight. M-103 contains over 30 stars in a somewhat wedge-shaped group. M-103 was discovered by Pierre Mechain, and was added to Charles Messier's catalog the same year, as number 103.
This image, acquired on September 16, 2015 is a 20 minute integration of 100 second exposures through the Celestron C-11 at f/2, using the HyperStar III imaging system and the Starlight Express SXVR-H694C color CCD camera, operating at -10 degrees below ambient temperature and binned 1 X 1. Guided, captured and combined using Maxim DL5 Pro. Post processed using PhotoShop CS2, Gradient XTerminator, StarShrink, Carboni's Astro Tools and NoiseWare.