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M20 and M21 in Sagittarius



Scope: Mak-Newt 152 mm  f/4.8, Location: Laguna Mountains, CA,   10 July 2010  Camera: ST8300M

Exposure:  10 x 7 min H-Alpha Exposure (1x1), 15 x 3 min UV/IR Block Luminance,  8 x 2 min RGB exposures (2x2).

Processing: Images were captured with CCDSoft. Aligned/stacked and dark subtracted in Astroart ; Sigma Combine method was used for stacking subs.  All channels were scaled and equalized in Astroart.  Channels were co-registered in Astroart. G2V  factors  were applied to color channels in Astroart.  The 7 minute H-Alpha block exposures were combined with the 3 minute luminance exposures  for the main luminance construction with level adjustments and curves to bring out object features. Some Levels and Curves were selectively applied excluding the core area.  LRGB combine was done in Photoshop. Saturation adjustments were selectively applied excluding the core area. Core area exclusion on some portions of Levels, Curves, and Saturation was to avoid core over brightening and out of Gamut.   Sharpening was done on the luminance channel. Final touches and color balance in Photoshop. Final Image size is approximately 3352x2532 (resized to 2800x2115).

North is up in this image. This image contains two well known objects - the emission/reflection nebula M20 (also known as the Trifid) and the open cluster M21. M20 is in the lower right and M21 is the cluster that somewhat resembles a diamond ring in the upper left. M20 lies about 5,200 light years distant from Earth; M21 lies a bit closer at about 4,250 light years distant from Earth. M20 can be seen separately here in an earlier image. M21 can be seen separately here in an earlier image.    Horizontal FOV is 88 arc minutes.

Image center is approximately - Equatorial 2000: RA: 18h 03m 18s Dec: -2253'03" 


All images and content remain the property of Jim Thommes - copyright 2003 - 2012

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