Nebulae in Orion. True-colour optical image of nebulae in the constellation Orion. At lower centre is the famous Orion nebula (M42 & M43), a starbirth region 1500 light years from Earth. It glows due to ionisation of its hydrogen gas by hot young stars embedded in it. At upper left is the Horsehead nebula, formed from the intrusion of the dark cloud B33 into the emission nebula IC 434. Just above the Horsehead is the star Alnitak, or Zeta Orionis. Above the Orion nebula is a smaller nebula made up of NGC 1973-1977. The bright star at top centre is Epsilon Orionis. This image was produced by digitally combining photographs taken by the UK Schmidt Telescope in blue and red light.