Omega Nebula. Optical image of the Omega Nebula (M17 or NGC 6618). This is an emission nebula, where hot, young stars in the centre of the nebula ionise surrounding clouds of hydrogen gas and make them glow. Such nebulae, known as HII regions, are known to be associated with star formation. Part of the nebula is obscured by a dark dust lane (top left to lower left). The Omega Nebula lies in the constellation Sagittarius, about 6000 light years from Earth. This image was produced using the Canada-France-Hawaii Telescope, Mauna Kea, Hawaii, USA.