Trifid nebula. infrared space telescope image of the Trifid nebula, an emission nebula that lies around 5400 light years from Earth in the constellation Sagittarius. Colours represent different wavelengths of infrared light. The main green cloud consists of hydrogen gas. Within this is the Trifid nebula, where radiation and winds from massive stars have blown a cavity into the surrounding dust and gas. The blue stars scattered around the picture are older, and lie between Earth and the Trifid nebula. The baby stars in the Trifid will eventually look similar to those foreground stars. The red cloud at upper right is gas heated by a group of very young stars. Imaged by NASA's WISE (Wide-field Infrared Survey Explorer) spacecraft.