M13 The great globular cluster in Hercules

This globular star cluster is visible to the naked eye shining at magnitude 5.8. It lies in the constellation of Hercules at a distance of about 22,000 light years .The sky conditions were hazy with  a bright full moon. I captured a composition of sub frames, five minutes and sixty seconds . I combined them together to avoid core saturation revealing inner and outer detail through out the entire image . I also took matching dark frames and flat field frames to avoid vignetting . I was using a ten inch f/4.8 reflector , PHD auto guiding and an Atik 383L CCD camera. The total exposure times were twenty minutes for each colour filter.