This is my image of the Crescent Nebula (NGC 6888) that I captured in October 2016.  NGC 6888 is an emission nebula having a Wolf Rayet star (WR136) near its center. WR 136 is 250,000 times brighter than the Sun with a mass 15 times greater. The star ejected a shell of material when it became a supergiant about 180,000 years ago; that shell continues to expand at 80 km/sec. An even faster stellar wind travels outward from WR 136 at 1,700 km/sec and shapes the shell into the form we presently see. UV radiation emitted from WR 136 ionizes hydrogen atoms surrounding the star; the separated hydrogen electrons subsequently recombine with hydrogen protons thereby emitting photons at a wavelength of 6563 Angstroms having a reddish color which is why the nebula is primarily red.

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I captured this image using a C11 SCT, a monochrome ATIK 460EX main imaging camera, a Lodestar X2 guide camera, an On Axis Guider, an F/6.3 Reducer,a 3nm H-alpha filter, a 3 nm O-III filter and a Starlight Instruments motorized programmable focuser control system. I recorded fifteen 15 minute and one 30 minute camera exposures in the H-alpha channel and eight 15 minute camera exposures in the O-III channel to form this image over a total integration time of 6.25 hours.