Orion Nebula (Messier 42, M42, or NGC 1976) in LPR filter Green; Ektar 1000 film 16' scope. The Orion nebula is a huge cloud of gas which glows due to the ionization of the hydrogen it contains by ultraviolet radiation from hot young stars within it. It is the nearest large emission nebula (or HII region) to Earth, lying 1500 light years away in the constellation Orion.