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Astronomers have their radio telescopes tuned to receive signals from alien worlds. But is anybody out there?
(This program is no longer available for online streaming.) In 1960 an inquisitive astronomer named Frank Drake aimed a radio telescope at a couple of nearby stars and started listening. Nearly 50 years later we're still listening, and SETI—the Search for Extraterrestrial Intelligence—has just expanded to begin the systematic survey of millions of star systems for signs of advanced civilizations. The Allen Telescope will eventually comprise 350 dish antennas, all working in unison to answer the question: Are we alone?