CITSO Blog: Floating on a silted stream

CITSO Blog: Floating on a silted stream

Cocoon Nebula (IC5146) in Cygnus

Sky & Telescope on-line Editor's Choice!
Published in Journal of the RASC October 2014

Imaged Summer 2013, Processing completed August 2014

Click the image for the high resolution version!

Cocoon Nebula (IC5146) in Cygnus

Imaged Summer 2013, 12+ hours collected, 10+ hours processed.

L=300 minutes (1X1); R=130m, G=110m, B=110m (all 2x2), Subs=10m.
Final image binned 2x2 owing to relatively poor seeing conditions.
Final image scale: 1.26"/pixel. Field of view: approximately 3/4 degree.

Telescope=PlaneWave CDK17, Camera=Apogee U16M, Mount=Paramount ME.
Astrodon filters and MOAG, Starlight Xpress Lodestar guide camera.

Frames acquired TheSky X, MaxIm DL, and Focusmax.
Processed with PixInsight and CCDInspector.

This is the frst of three imaging projects from the summer of 2013, and it's taken me a whole year to finally complete processing it (egads!). The other two projects are still to come ;).

This lovely object lies in a star-jeweled region of the Milky Way in Cygnus. I hope that this framing of the image may fancifully suggest a fall-coloured leaf floating along a silted stream, with the stars crowding the corners giving the impression of multicoloured gems deposited there by the current ;).

The dark dust lane extends for several degrees, and in binoculars under dark skies it shows up as an inky-black hole in a stunningly rich star field (the emission nebula cannot be seen with binoculars, and is very faint even in large telescopes). This dust lane is one of Gary Seronik's 99 Binocular Highlights; Seronik calls it "The Road to the Cocoon". BTW, I highly recommend Seronik's book, which opened my eyes to the many beautiful and compelling celestial treasures within easy reach of binoculars under dark skies. Checkout this amazing wide-field image of the Cocoon and its surroundings by Fabian Neyer, and this superb closeup by Neil Fleming and David Plesko.

This is the 2nd time that I've imaged the Cocoon: my first effort was a much shorter exposure in June 2010, my very first year of operation of the Cabin in the Sky observatory. I think a comparison between the two renditions shows some progress in my image capture and processing techniques ;)- checkout my first attempt here!

I found it very challenging to stretch this image in such a way as to reveal the faint, dark nebulosity that "cocoons" the central emission nebula, without blowing out the rest of the image, and without generating too much noise in the low signal regions. The subtle blue reflection nebula to the right of the image centre was also a challenge to bring out.

I also struggled with the crowded star field, using PixInsight's MorphologicalTransformation tool to shrink the small stars (a standard image processing trick), which would otherwise detract much too strongly from the nebulae; however, despite my best efforts, I think the star field is still too busy :(. This is also the first time that I downsampled an image for its final presentation, since the seeing conditions in summer 2013 were relatively poor: the final image here is binned 2x2, with an image scale of 1.26"/pixel.

DownX2 for Asterik