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Astrophotography by Bob Franke

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NGC 6888 The Crescent Nebula

           Click the full screen zoom button       ^
Click the image to Zoom and Pan    

Click here to view the image without Zoomify (1950 x 1300)




12.5" RCOS @  ~f/9 (2880 mm fl) 1.28 arcsec / pixel.  Zoomify image scale is 1.28 to 3.33 arcsec / pixel.


Paramount ME


SBIG STL-11000 w/ internal filter wheel, AstroDon Gen I Filters

Acquisition Data

6/19/2010 to 8/5/2010 Chino Valley, AZ... with CCDAutoPilot3 & CCDSoft, AOL guided


Hα    600 min. (20 x 30 min. bin 2x2)
OIII  660 min. (22 x 30 min. bin 2x2)

RGB  225 min. (  5 x 15 min each, bin 2x2)

Hα [OIII + 20%Hα] [OIII + 20% Hα] and an overlay of RGB stars colors.

Click here for an Ha filtered b/w version.


  • CCDSoft, CCDStack, Photoshop CS w/ the Fits Liberator plugin. Noel Carboni's actions.

  • eXcalibrator for (b-v), (v-r) star color calibration, using 26 stars from the NOMAD1 database.

  • PixFix32 (pre-beta) to repair hot/cold pixels and column defects.

  • CCDStack to calibrate, register, normalize, data reject, combine the sub exposures.

  • PhotoShop for color combine &  on-linear stretching.


North is to top.

NGC 6888, the Crescent Nebula, is located the constellation Cygnus at a distance of about 5,000 light-years. The nebula is created by the bright central star, HD 192163. About 400,000 years ago, the star ejected material, when it became a red giant. Then, about 150,000 years later, HD 192163 shed its outer envelope into a strong stellar wind, and became a Wolf-Rayet star (WR 136). The second explosion eventually over took the previous ejected gas. This collision formed and lit up the nebula we see today. Wr 136 is expected to end its life with a supernova explosion, sometime in the next million years.


This synthetic color image was created by mapping Ha data to red and OIII filtered data to green and blue. This creates an image with hydrogen gas shown as red and doubly ionized oxygen is teal.