This is a faint and hard to photograph nebula. It's located high overhead, about 4700 light years away in the mid summer Milky Way in the constellation of Cygnus the Swan. The Crescent Nebula, also known as Caldwell 27 (C27) and NGC 6888, is being created by the bright star just to the upper right of center here.  That star began its life just 4.5 million years ago (our sun is 4.5 billion years old) as a blue giant type O star, the most luminous classification of stars. It has already gone through its red giant phase where it sloughed off and blew away huge quantities of it's outer layers. Now it is in what is called its Wolf-Rayet stage, a brief stage of maybe 250,000 years where its intensely hot but still massive deeper layers are exposed. The intense nuclear fires still burning produce strong ultraviolet radiation and a fierce solar wind of ionized particles, together which are ionizing,  lighting up, and running into the previously ejected material, - creating among other things its namesake crescent shaped wave front..

10" Schmidt Cassegrain Telescope at f7.6, with Canon 5D Mark II, IDAS LP-2 filter.
12 photos of 600 seconds each at ISO 1600.
All 12 photos were aligned and averaged together into one, and then brightness and contrast enhanced. The above is a cropped version of the original.