NGC6888 – The Crescent Nebula

The Crescent Nebula, in the constellation Cygnus, is the result of the bright central star entering the second phase of burning out. The hypothesis is that in its first phase, the red giant star used up all its hydrogen fuel and expelled its outer shell of gas. About 250,000 years ago, the star evolved into a Wolf-Rayet type and began ejecting its outer shell in a strong stellar wind. The wind collided with the hydrogen cloud from the first phase, compacting it into complex shells. Strong ultraviolet radiation ionizes the hydrogen gas, causing it to glow red. The star, WR136, will likely explode as a supernova within the next million years.