Swan and Eagle nebulae, optical image. These are both emisison nebulae, clouds of gas and dust glowing red as the hydrogen gas is ionised by radiation from hot young stars within them. The Swan Nebula (M17, upper left) is located in the constellation of Sagittarius and is around 6000 light years from Earth. The Eagle Nebula (M16, lower right) lies around 7000 light years from Earth in the constellation Serpens. This image includes a filter for the light from hydrogen (H-alpha) ions.