Crescent nebula (NGC 6888). The nebula is a glowing shell of gas cast off by the central star WR 136. WR 136 is a Wolf-Rayet star, a rare type of hot, massive star that loses mass rapidly through a strong and dusty stellar wind. This nebula lies around 4700 light years from Earth in the constellation Cygnus. Different colours represent different ionised gases; sulphur is red, hydrogen is green and oxygen is blue.