For more than 40 years, astronomers have used microwave radio telescopes to try to detect signals from extraterrestrial aliens. Both Guglielmo Marconi and Nikola Tesla at one time claimed they had detected radio signals from aliens, but it was not until 1959 that a thorough search began. In that year, Cornell University astronomers Phillip Morrison and Giuseppi Cocconi proposed using large radio telescopes to try to receive these messages, if they in fact exist. They claimed that any intelligent civilization would probably broadcast at a frequency of 21 centimeters, because this is the emission frequency of hydrogen, the most common atom in the universe.
The search continues today as a smaller, privately funded project, and over the years public awareness of SETI has grown. Its profile was raised considerably following the release of Carl Sagan's book Contact and its subsequent film adaptation, which featured fictionalized SETI scientists at work at the Arecibo, Puerto Rico radio telescope facility and the Very Large Array radio telescope complex in New Mexico, both of which have actually been used for SETI research in the past.