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Orion nebula, optical image. The Orion nebula can be seen with the naked eye as a fuzzy patch in the constellation Orion. This part of it comprises two nebulae: M42 (pink, upper centre) and M43, the small round nebula immediately above M42. These nebulae glow pink as the hydrogen they contain is ionised by radiation from hot young stars that recently formed inside them. In the case of M42, the stars that light it up are a group of four known as the Trapezium, in the brightest part of the nebula. The nebulae lie around 1500 light years from Earth. (KEYSTONE/SCIENCE PHOTO LIBRARY/ROBERT GENDLER)