Trifid Nebula (M20, NGC 6514), artwork. Part of this nebula (cloud of gas and dust) glows red due to the ionisation of the hydrogen gas by the hot and bright stars born at its centre (bright area, upper centre). This is called an emission nebula. The M20 emission nebula is partially obscured by a dark nebula (B85) in front of it, giving rise to a three-lobed appearance. The M20 nebula is not all ionised, with parts of it reflecting starlight as a blue colour (lower centre). This is a reflection nebula. The Trifid Nebula lies around 9000 light years from Earth in the constellation Sagittarius.