M-21 (NGC-6531) is an open star cluster located in western Sagittarius just NE of M-20, the Trifid Nebula. It is a relatively young cluster, being less than 5 million years old, and consists of 57 stars, most of which are blue-white giants. It lies approximately 3000 light years from earth.
This image, acquired on July 14, 2012, is a 20 minute integration of 90 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.