M13 - The Great Globular Cluster in Hercules
M13 - The Great Globular Cluster in Hercules
M13 - The Great Globular Cluster in Hercules
M13 is one of the most impressive globular clusters in the sky. The cluster is about 25,000 light years from Earth, and contains several hundred thousand stars. M13 subtends about 20 arc minutes in the sky, which makes it about 2/3 the size of a full moon. If you look closely, you can see the small galaxy IC 4617 at the top of the image at about the 11:00 position plus several other background galaxies scattered throughout the image.

In this image, North is Up. This image is cropped to 78% of the original full frame.

Exposure Details
Lens Celestron C-8 SCT with Celestron focal reducer
Focal Length 1160mm
Focal Ratio f/5.8
Mount Schaefer GEM - 7 1/2
Guiding ONAG On-Axis Guider, Lodestar autoguider, PHD Guiding
Camera Canon 450D - Gary Honis modified
Exposure 236 subexposures of 120 seconds each at ISO 400 - just under 8 hours total
Calibration 30 darks, 30 flats, 30 bias
Date June 10, 11, and 15, 2012
Temperature 56F on 6/10, 59F on 6/11, 60F on 6/15
SQM Reading 21.0 (Bortle 4.5) on 6/10 and 6/11, 20.8 (Bortle 4) on 6/15
Seeing 5/5 on 6/10, 4/5 on 6/11 and 6/15
Location Pine Mountain Club, California
Software Used Images Plus 4.5 for camera control, calibration, stacking, digital development, multiresolution sharpening, smoothing and noise reduction. Photoshop CS5 used for levels and curves, color correction, selective color, high pass filter, star shrinking, lab color, saturation adjustments, lens correction, and smart sharpen. Gradient Xterminator for gradient removal. Carboni Tools for additional saturation adjustments, noise reduction, and smoothing. HLVG for additional color correction.
Notes I was fortunate to have some very good seeing conditions on each of the nights that I photographed this object. As a result, this image ended up being quite sharp, and I'm quite happy with the detail I captured.

This image won 1st place in Astrophotogallery.org's June 2012 Cluster category.

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