Astronomy Picture of the Day

Explanation: The largest radio telescopes in the world are working together to create a new map of the surface of Venus. The surface of Venus is unusually hidden by a thick atmosphere of mostly carbon dioxide gas. These thick clouds are transparent, however, to radar signals sent and received from Earth. The two radio telescopes generating the most powerful radar ever are the Arecibo Telescope in Puerto Rico and the new Robert C. Byrd Green Bank Telescope in West Virginia. The new survey will resolve details as fine a one-kilometre across, and will be inspected for changes since the last major radar map was made by NASA's Magellan spacecraft that orbited Venus from 1990 to 1994. Pictured above is part of a preliminary image showing details as small as five-kilometres across.