Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

Explanation: This forest of snow and ice penitentes reflects moonlight shinning across the Chajnantor plateau. The region lies in the Chilean Andes at an altitude of 5,000 meters, not far from one of planet Earth's major astronomical observatories, the Atacama Large Millimeter/submillimeter Array. Up to several meters 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 constellationsPegasus, Andromeda, and Perseus near the panorama's left edge. Bright and colorful stars of Orion the Hunter are near center, with the Large Magellanic Cloud and the South Celestial Pole on the far right.