Multiple exposures are made to collect enough light for an image that would otherwise not be evident to the eye.
Credit: Ian Sharp
The cloud of dust glimmering in this image represents the Crescent Nebula in the constellation Cygnus.
The nebula, also known as NGC 6888, lies about 5,000 light-years away in Cygnus, the swan. (A light-year is the distance light travels in one year — about 6 trillion miles or 10 trillion kilometers). The image was taken by astrophotographer Ian Sharp in September 2008.
NGC 6888 is an emission nebula formed by stellar winds colliding with the Wolf-Rayet star WR 136. Wolf-Rayet stars are very hot, massive stars that are blowing off their outer layers.
The collision between wind and star, which occurred when WR 136 entered its red giant phase, caused the shell-like structure with waves within. The star is expected to explode and become a supernova in the next million years.
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