Orion nebula. True-colour optical image of the great Orion nebula (M42 & M43, lower centre) and the associated reflection nebula NGC 1977 (top). These nebulae lie around 1500 light years away in the constellation Orion. M42 and M43 are HII regions, areas of gas (mainly hydrogen) and dust where newly born stars excite the gas, causing it to glow. NGC 1977 is a reflection nebula, lit only by reflecting light from nearby stars. M42 and M43 are excited by a group of stars (the Trapezium) embedded in them. The stars are here obscured by the bright central region. This image was produced by digitally combining photographs taken by the UK Schmidt Telescope in blue and red light.