SUPERCEDED-NEWER VERSION AVAILABLE---M17 - The Omega Nebula in Sagittarius
SUPERCEDED-NEWER VERSION AVAILABLE---M17 - The Omega Nebula in Sagittarius
SUPERCEDED-NEWER VERSION AVAILABLE---M17 - The Omega Nebula in Sagittarius
M17 is one of the treasures of Sagittarius. Commonly called the Omega Nebula, it also known as the Swan Nebula (because it looks like a swan) as well as the Checkmark Nebula, the Lobster Nebula, and NGC 6618

In this image, North is Down. This image is cropped to 81% of the original full frame.

Exposure Details
Lens Celestron C-8 SCT with Celestron focal reducer
Focal Length 1260mm
Focal Ratio f/6.3
 
Mount Schaefer GEM - 7 1/2
Guiding 80mm f/11 guidescope with PHD Guiding
 
Camera Canon 20Da
Exposure 87 subexposures of 180 seconds each at ISO 1600 - about 4 1/3 hours total
Calibration 30 darks, 30 flats, 30 bias
 
Date August 28, 29, and 30, 2011
Temperature 70F on 8/28, 65F on 8/29, 61F on 8/30
SQM Reading
Seeing 4 of 5 on all 3 nights
Location Pine Mountain Club, California
 
Software Used Images Plus 4.0 for camera control, calibration, stacking, digital development, and initial smoothing. Photoshop CS5 used for flat fielding, curves, color correction, saturation adjustments, star shrinking, and high pass filter. Carboni Actions for additional saturation adjustments and noise reduction.
Notes After reprocessing this image several times, I was finally able to bring out the faint outer nebulosity.