Astronomy Picture of the Day

Explanation: This forest of snow and ice penitentes reflects moonlight shining across the Chajnantor plateau. The region lies in the Chilean Andes at an altitude of 5,000 metres, not far from one of planet Earth's major astronomical observatories, the Atacama Large Millimetre/submillimetre Array. Up to several metres high, the flattened, sharp-edged shapes, and orientation of the penitentes tend to minimize their shadows at local noon. In the dry, cold, thin atmosphere, sublimation driven by sunlight is important for their formation. A direct transition from a solid to a gaseous state, sublimation shapes other solar system terrains too, like icy surfaces of comets and the polar caps of Mars. Above the dreamlike landscape stretches the southern night sky. Their own forms rooted in myth, look for the constellations Pegasus, Andromeda, and Perseus near the panorama's left edge. Bright and colourful stars of Orion the Hunter are near centre, with the Large Magellanic Cloud and the South Celestial Pole on the far right.