Crescent Nebula (NGC 6888) is the result of rapidly expanding shell of gas, surrounding a dying star at its center. The nebula appears as a crescent in many telescopes because most of the object is barely visible, just the bright outer “crescent” portion. It is approximately 18 trillion miles across and is formed by strong stellar winds given off by its central star. The star is going through the latter stage of star evolution with a burst of faster moving stellar winds, ejected approximately 250,000 years ago, running into much slower moving stellar winds, ejected by the star approximately 400,000 as it became a red giant.  The result is two shock waves coinciding, heating up and, in addition, being illuminated by ultraviolet radiation from the central star.

In 1867, the French team Wolf-Rayet identified a class of stars, such as this central star, as massive stars (large stars  over 20 times the mass of our sun) which are at a stage of their life where they are losing their mass rapidly by means of very strong stellar winds (speeds up to 4 ½ million miles per hour). The star at the center of the Crescent Nebula will eventually, in the next million years, go supernova with a final bright burst of gamma rays and, then, collapse in a final death throe -  when the core of the star collapses to form a black hole- pulling in the surrounding material. (combination of Ha:L:R:G:B filters at 90:120:50:50:50 minutes each)