The Horse Head and Flame Nebulae in Orion, optical image. The Horsehead Nebula's distinctive shape (centre right) is caused by dark nebula Barnard 33 (B 33). This cloud of dust and gas obscures the light from the emission nebula IC 434 that lies behind. The gas of this nebula glows as it is ionised by the radiation from hot stars. The Flame Nebula (NGC 2024, lower left) is also an emission nebula bisected by a dark dust cloud. The bright star above NGC 2024 is Alnitak (Zeta Orionis), one of the three stars in Orion's belt. The nebulae lie around 1500 light-years away in the constellation of Orion. Photographed in 2019 from the Cumeada Observatory in the Dark Sky Alqueva Reserve, Portugal.