Figure 3-54 Emission Spectra from Interstellar Gas Clouds (a) Stars in this interstellar gas cloud (NGC 2363) in the constellation Camelopardus (the Giraffe) emit blackbody spectra. Electrons in the cloud’s hydrogen gas absorb and reemit the red light from these stars. NGC 2363 is located some 10 million ly away. (b) The nebula NGC 604, located 2.7 million ly away in the constellation Triangulum, is also an interstellar gas cloud. The green glow is generated by doubly ionized oxygen atoms (O III; oxygen atoms missing two electrons) in the cloud that emit 501-nm photons. The Rosette Nebula is 3000 ly away.