The Arecibo Observatory is a radio telescope just over 1,000 feet (305 m) across, the largest single radio telescope. The main metal collecting dish sits fixed a hemispherical karst sinkhole. In addtion to being a radio telescope, the dish is also a powerful radar transmitter, and has been very useful in radar astronomy in our solar system. This transmitter is on a 900 ton platform known as 'the feed' hanging 500 feet (150 m) over the dish. The observatory is the primary location of the National