Orion constellation over the La Silla Observatory, Chile. Close to the horizon is the Pleiades open star cluster. Directly above Pleiades is Orion, which includes giant clouds and arcs of ionised gas (emission nebulae) seen here as red patches. The Milky Way is also visible, carving its way across the night sky. Airglow, produced by light in Earth's upper atmosphere, is green. The La Silla Observatory is located in the Atacama Desert at an altitude of 2400 metres, where there are some of the darkest night skies on Earth. It has been in operation since the 1960s.