Trifid nebula. True-colour optical image of the Trifid nebula (M20, NGC 6514) in the constellation Sagittarius. The pink part of the nebula is a glowing cloud of hydrogen gas ionised by the radiation from powerful central stars. It is crossed by dark lanes of dust which obscure the emitted light. Areas such as this are thought to be regions where star birth occurs. The blue area is a reflection nebula, a cloud of cool dust and gas which reflects the light of bright stars in it. The nebula lies around 6500 light years from Earth. This image was produced by digitally combining photographs taken by the UK Schmidt Telescope in blue and red light.