M103 is a loose and poor cluster and the number of members is a value of some contention. Various sources list the quantity of stars in M103 as ranging from 25 to 172. The cluster is somewhat remote, lying about 8,500 light-years from Earth. The cluster 's appearance is dominated by the non-member binary Struve 131, which has magnitudes 7 and 10. The two brightest cluster members, of about mag 10.5, are a B5 supergiant and a B2 giant. M103 contains one red giant star, of spectral type M6 and mag 10.8. The lot of main sequence stars indicate that the cluster is quite young, perhaps between 9 million and 22 million years. M103's angular diameter of 6 arc minutes corresponds to 15 light-years linear extension. This stellar swarm is approaching us at 37 km/sec.

Taken September 25, 2009, with the ST-8 and the 300mm Nikkor lens. Exposure is 5 minutes.
Taken August, 2005. Details not recorded but likely taken with the 402 camera and 300 lens.