Trifid Nebula: The Trifid Nebula (cataloged as Messier 20) is so called because it appears to have three lobes in the reddish part. This is a star-forming region, which includes an emission nebula (the reddish part), reflection nebula (blue part) and dark nebulae (the dark parts that appear to divide the emission nebula). The Trifid Nebula is approximately 5,200 light years from us, about 40 light years across, and glows brightly at an apparent magnitude of 6.3 (meaning possibly visible to the naked eye in the very darkest skies).

I previously photographed this with my small scope, as part of a much larger field, in Trifid Nebula and Lagoon Nebula photo.

I have presented the image here in two forms: A color version, and a gray-scale version showing only the Ha emisssions (click on the image to toggle between the two versions). I think it's interesting how graphically this comparision shows that the Ha emissions are only a part of the red spectrum; the blue parts of the color image surrounding the red nebula largely disappear in the Ha version.

Technical Information:

(LHaOIIIBR)(RHa)(GOIII)(BOIII): L-380; R-340; G-200; B-300; Ha-330; OIII-270. Luminance layer consists of a blending of data taken through an Astrodon Ha filter, OIII filter, luminance filter, red-pass filter and blue-pass filter; red channel consists of a blending of the Ha and red-filtered data; green channel consists of a blending of the green-filtered and OIII-filtered data; blue channel consists of a blending of the blue-filtered data and the OIII-filtered data. All Ha-filtered images and OIII-filtered images were 30-minute exposures; individual color images were 20-minute exposures. All images unbinned.

Equipment: RC Optical Systems 14.5 inch Ritchey–Chrétien carbon fiber truss telescope, with ion-milled optics, SBIG STL11000M with internal color filter wheel (Astrodon Type II filter set), on a Bisque Paramount ME German Equatorial Mount.

Image Acquisition/Camera Control: Maxim DL, controlled with ACP, working in concert with TheSky v6, guided by an SBIG AO-L attached to a MOAG.

Processing: All images calibrated (darks and dawn flats), aligned and combined in Pixinsight. Color combine in Pixinsight. Finish work (curves and levels, adjustment of contrast, and some sharpening of the luminance layer) was done in Photoshop CS5.

Location: Data acquired remotely from Fair Dinkum Skies, Moorook, South Australia.

Date: Images taken on many, many nights from April 2015 through July 2015; conditions were uniformly atrocious, with rain, clouds and fog the norm during that time. Image posted on July 28, 2015.

CCD Chip temperature: -15C

Copyright 2015 Mark de Regt

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