Between and around the famous Orion and Horsehead nebulae lies a cold cloud of gas, mostly hydrogen, mixed with traces of dust. Invisible to the eye, the molecules of gas are seen at radio wavelengths and are known as molecular clouds. When the dark surface of such a cloud is lilluminated by the light from very hot stars, as here, the energetic radiation makes the gas glow as it evaporates from the tenuous dust then ionises. The starlight gradually eats into the dust cloud, leaving the luminous, lumpy surface and sweeping wisps of dusty gas emerging from it, like a cosmic waterfall.

Image was derived from a red-light plate taken on the AAT.