IC  2631

IC 2631

Reflection Nebula in Chamaeleon

Constellation: Chamaeleon
Ra: 11h 09m 51s
Dec: -76d 36m 41s
Distance: 500 light years
Image Size: 34' x 34'
North: Up; East left



IC 2631 (Ced 112) is a brilliant blue reflection nebula surrounding the young star, HD973000, about 500 light years distant in the southern constellation of Chamaeleon. As can be seen in the image above, the Chamaeleon cloud complex is a large region of gas and dust where new stars are forming.  The dust partially or nearly totally obscures the stars within and behind it.  HD973000 is a T Tauri star, the youngest visible stage for relatively small stars.  Eventually they will lose mass and shrink but for now they will spend billions of years as a main sequence star.  The image shows the complexity of the dust cloud surrounding the bright reflection nebula.  

Published in Astronomy, July 2016, p. 72

Exposure: 7.5 hours RGB + synthetic luminance
Telescope: PlaneWave CDK20 0.5m f/6.8 reflector
Mount: PlaneWave Ascension A200h
Oag: Astrodon MonsterMOAG
Acquisition: ACP8-Expert
Calibration: CCDStack2
Observatory Site: iTelescope.net, Siding Spring, NSW, Australia
Camera: SBIG STX16803
Filters: Astrodon Gen 2 E-Series RGB
Guider: SBIG ST-i
Camera Operation: MaximDL4.24
Processing: Photoshop cc 2015
Image Date: 03/01/2016 - 03/03/2016


  1. Sakib

    Absolutely stunning! It looks like a tranquil watercolour painting on a cosmic scale! You can even see some Herbig Haro objects and the background galaxies hiding in the dust are a nice bonus. I have a question, what is synthetic luminance and why didn’t you take regular luminance?

  2. Josep

    Impressive! especially the fine detail in the reflection nebula. I understand that your synthetic Lum is a mix of RGB, but I am also curious about the reason not to take directly Lum, that might have shown more info.

    • astrodon

      It is my understanding that the LRGB method involved unbinned, high-resolution luminance, which is then colored by shorter, lower-res, binned RGB color data. I’ve primarily used short, unbinned RGB color data to provide realistic color in my narrowband images. Stars produced solely from narrowband filters can look terrible. I take the color data unbinned so the stars are a better match in size and the exposures, typically 5 min., are short enough not to get much of the nebula. The RGB data for this image is deeper, 10 min exposures and several hours of them. So, the resulting color data is much deeper. So, combining the master RGB data into a synthetic luminance makes good use of the time already invested without having to take hours of luminance data separately. You can deconvolute the synthetic luminance and use other techniques, like high pass filtering, luminance masking, etc as you would with a real luminance. Then you colorize it with the unbinned color. In short, it seems to save time. I may be wrong from a purely mathematical perspective, but it seems to work.

      • Sakib

        Thanks for the explanation, I’m trying to understand the technical aspects of astrophotography better but however remembering them is a different matter. Couldn’t unbinned luminance be combined with unbinned RGB? Also what is the difference between binned and unbinned? I wonder if Ha exposures for this region might show additional detail?

  3. Josep

    Thanks! Well, it really works! Again, a nice nebula and a pretty artwork.


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