Instrument

12.5" RCOS @  ~f/9 (2880 mm fl) 0.643 arcsec / pixel.  Shown resampled to 1.84 arcsec / pixel.

Mount

Paramount ME

Camera

SBIG STL-11000 w/ internal filter wheel, AstroDon Filters

Acquisition Data

6/12/2009 to 6/22/2009  Chino Valley, AZ

Exposure

Lum    120 min (11 x 10 min, bin 1x1)

RGB    360 min (12 x 10 min each, bin 1x1)

Software

CCDSoft, CCDStack, Photoshop CS w/ the Fits Liberator plugin, Noel Carboni's actions and Russ Croman's Gradient Exterminator

CCDStack to register, normalize, data reject, combine sub exposures, pixel math and RGB combine.  eXcalibrator (pre-beta) for color calibration.

PhotoShop for luminance processing and LRGB combine.

Comment

North is to the top.

The M12 globular cluster, NGC 6218, is in the constellation Ophiuchus and was discovered by Charles Messier on May 30, 1764. The cluster is 16,000 light-years from Earth and has a spatial diameter of about 75 light-years. It is loosely packed and was once thought to be a tightly concentrated open cluster. M12 has thirteen variable stars.