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NGC 6888,  the  Crescent  Nebula

in Cygnus

      The Crescent Nebula is one of many emission nebulas in the constellation Cygnus. It was formed from the explosion of a dying star and producing reddish light as a result of fluorescence of hydrogen gas at a wavelength of 653.6 nM. North is to the lower right in this image. The rich star field in and around it shows that it lies in the visible Milky Way in the summer sky.

       The name Crescent is the result of its visual appearance in the telescope, which shows only the bright rim around the right and lower edge. However, as shown by the image, the nebula is shaped like a potato (or football). Long exposures are needed to bring up the fainter portions of the structure. For this image the total exposure time was 255 minutes, over 4 hours. For a better view of the fine structure in the nebula, see the H-alpha image here.

 Date

 2003 August 9 and 24

 Scope

 RCOS Ritchey-Chretien 12.5 inch at f4.5 on AP 1200GTO mount, guided with ST-4 on

 guidescope.  Camera: SBIG ST-10XME at -15 C and CFW-8a color wheel, controlled with 

 MaxIm DL/CCD.

 Exposure

 R, G, and B exposures 9 x 5 min. Luminance = H-alpha 3 x 20 min + 6 x 10 min, 3 nM filter.

 Processing  

 Frames calibrated and RGB combined in MaxIm and debloomed with the CCD-NewAstro

 Debloomer. The luminance layer was subjected to  DDP processing in MaxIm. Luminance

 registered with RegiStar. Final processing with Levels and Curves in Photoshop.

 

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