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The Details
NGC 6888 Crescent Nebula in Cygnus
Astro-Physics 160 EDF Refractor at f/7.7
Astro-Physics 1200 GTO
Tru-Balance 5nm H-alpha and 3nm OIII filters
29 June 2011, 01 & 02 July 2011
Mount Wilson Observatory - Mount Wilson, CA
Ha 8 x 1800 sec 1x1 bin; OIII 14 x 1800 sec 1 x 1 bin - Total exposure time 11 hours

Maxim DL/CCD, CCDStack 2, Photoshop CS5
Field of View: 40’24" x 27’12" centered on RA 20h12m14s
DEC +38°18’47” (2000.0). North angle 337.7°; east 90° CCW from north

This is an extremely interesting object formed by a super hot, short lived, massive Wolf-Rayet star. At a point in the past this rare type star swelled to a red giant stage and ejected it outer layers into space. As the star then contracted because of the crushing force of gravity, intense radiation from the exposed, hot inner layers began stripping gas away from the star at speeds in excess of 3.5 million miles per hour. When these high speed stellar winds caught up to and collided with the red giant ejecta, the shell of the Crescent Nebula was born in the resulting shock wave. The Wolf-Rayet star responsible for this creating this beautiful object is the bright star near the center of the nebula and is designated as HD 192163. It is theorized that HD 192163 will likely explode as a supernova sometime in the future. Lying approximately 4700 light years from earth, the Crescent Nebula is about 16 light years wide and 25 light years long.

This "false color" image was created using a bicolor technique for combining Ha and OIII images developed by amateur astronomer Steve Cannistra ( Using data from these two filters, a synthetic green channel (Sg) was created in Photoshop. The color assignments used were Ha (red), Sg (green), OIII (blue). The finished image is a composite Ha:OIII(Ha:Sg:OIII), using a blend of the Ha and OIII channels as a luminance layer to enhance detail in the final representation.

This image was published in the Gallery section of the January 2012 Sky & Telescope magazine.





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