NGC 6888 - The Crescent Nebula in Hydrogen-Alpha light


Copyright 2008 Hap Griffin

Powerful radiation winds blowing from the massive star, HD 192163 in the center of this photograph, created this nebula. About 400,000 years ago, HD 192163 expanded enormously to become a red giant and ejected its outer layers. 200,000 years later, the intense radiation from the exposed hot, inner layer of the star began pushing gas away at speeds in excess of 3 million miles per hour.  Information gathered by the Chandra X-Ray satellite leads researchers to predict that HD 192163 will explode as a supernova in approximately 100,000 years.

This image was taken through a narrowband Baader hydrogen-alpha filter.  Hydrogen gas, when excited by radiation to the point where it emits its own glow emits a deep red light at a wavelength of 656.3 nano-meters.  The filter used here passes only that wavelength and a very narrow window of wavelengths on either side...thus it is essentially a single color image and reproduced here as shades of gray.  One advantage to shooting these emission nebulae through such a filter is that increased detail can be seen that is sometimes lost in the maze of colors in a full color image.  Another advantage is that such photographs can be taken in full moonlight that would spoil a full-color image.  This was captured with the moon only about 40 degrees away in the sky..  

NGC 6888 lies at a distance of 5000 light-years.


Date/Location:    April 26, 2008   Griffin-Hunter Observatory near Bethune, SC
Instrument:    Canon 40D Digital SLR (modified)  through Orion 10" Newtonian w/ Baader MPCC
Focal Ratio:   F/4.7
Guiding:    Auto via SBIG ST-402 through Orion ED80 refractor
Conditions:    Clear and cool 
Weather:    50 F
Exposure: 190 minutes total (38 x 5 minutes @ ISO 800)
Filters:    Baader 7 nm HA filter, Baader UV/IR block filter internal to camera
Processing:    De-bayering, calibration, selection of red channel data, alignment, stacking, Digital Development, Richarson-Lucy Deconvolution in ImagesPlus 3.0 .  Finished in Photoshop CS3.