Galaxies, Stars and Nebulae series Like the fury of a raging sea, this bubbly ocean of glowing hydrogen, oxygen, and sulphur gas lies in the extremely massive and luminous molecular nebula Messier 17. This Hubble photograph captures a small region within Messier 17 (M17), a hotbed of star formation. M17, also known as the Omega or Swan Nebula, is located about 5500 light-years away in the Sagittarius constellation. Ultraviolet radiation is carving and heating the surfaces of cold hydrogen gas clouds and the warmed surfaces glow orange and red. The intense heat and pressure causes some material to stream away from the surface, creating the glowing veil of even hotter green-coloured gas that masks background structures. The colours in the image represent various gases. Red represents sulphur; green, hydrogen; and blue, oxygen. Image code: eroton Image credit: NASA, the ACS Science Team