NGC 6888: Crescent Nebula

The Crescent Nebula (also known as NGC 6888, Caldwell 27 or Sharpless 105) is an emission nebula in the constellation Swan, about 5000 l.y. away from Earth.
It was formed by the fast stellar wind from the "Wolf-Rayet star" WR 136 (HD 192163) colliding with and energizing the slower moving wind ejected by the star itsself when it became a red giant around 250000-400000 years ago.