Crescent Nebula & Sharpless 2-108
5 x 1200 seconds + 8 x 600 seconds with 5nm Ha filter.
Top right of the image is the Crescent Nebula & the large area of nebulosity is Sharpless 2-108.
About 4,700 light years away the Crescent Nebula, NGC 6888, was formed by a fast stellar wind from the Wolf-Rayet star HD 192163, also known as WR 136. The star is shedding its outer envelope, ejecting the equivalent of the Sun's mass every 10,000 years. This stellar wind is colliding with, and energizing, a slower-moving wind ejected by the star when it became a red giant around 400,000 years ago. The result of the collision is a shell about 25 light-years across. Two shock waves, one moving outward and one moving inward, heats the stellar wind to X-ray-emitting temperatures. The central star WR 136 will probably undergo a supernova explosion sometime in the next million years.