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the crescent nebula

 

Often called the Crescent Nebula, NGC 6888 is a rather peculiar object found within the extremely rich and colorful starfields of southern Cygnus. The nebula, itself, is actually a wind-blown bubble of rapidly moving material shed by the massive 7.5 magnitude star located nearest the Crescent's center. This star is known as HD 192163 and is classified as Wolf-Rayet type star. Wolf-Rayet stars are thought to represent an evolutionary phase in the lives of extremely massive stars. Such stars burn through their initial hydrogen envlopes at violent rates, therefore exhibiting strong stellar winds and rather odd spectra. Often approaching 3000 km/sec, the star's fierce winds induce vigorous and sometimes episodic mass-loss in the form of shells of gas being expelled from the stellar atmosphere. Since W-R stars commonly exceed a temperature of 30,000 Kelvin, these gaseous ejections are sometimes ionized and form visually observable nebulae, such as NGC 6888 above. The visible part of the Crescent alone contains more than twice the amount of material currently present in our very own Sun. Otehr objects of interest include the sparse open star cluster Dolidze 39 located in the far lower lefthand corner of the image, as well as filamentary structure from the Simeis 53 nebula at the far upper right. My favorite part of the entire image is the rather bizarre anonymous dark nebula associated with the ruddy nebula DWB 25 found near the very top just left of center. Image taken with homemade 8-inch f/5.4 astrograph and SBIG STL-11000M. LRGB image composed of 60 minutes each R,G,B and synthetic L channel. Click on the above image for the high resolution version.