Telescope: Celestron C-14 - Camera: ST-10XME - Mount: MI-250
Exposure: L(Schuler Ha 10nm) = 120 min. (15 min. sub-exposures)
NGC 6888 is located approximately 4,700 light years from earth and is known as the Crescent Nebula because of its distinctive shape. Technically it is classified as a Wolf-Rayet nebula. Such a nebula is formed when a very hot, massive star ejects its outer layers in a strong stellar wind. In the case of the Crescent Nebula the star responsible (WR 136) is the bright star in the center of the image above. As the star ages it begins to shrink and grow much hotter. Its stellar wind becomes more rarefied but much faster. This fast stellar wind then collides with the older ejected gas and pushes it into a relative dense bubble. The radiation from the hot central star excites the gas, principally hydrogen, causing it to shine in the red spectrum typical of an emission nebula. The image above was captured using a hydrogen alpha filter
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