Early SETI: Project Ozma, Arecibo Message
In 1960, radioastronomer Frank D. Drake, then at the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia, carried out humanity's first attempt to detect interstellar radio transmissions. Project Ozma was named after the queen of L. Frank Baum's imaginary land of Oz -- a place "very far away, difficult to reach, and populated by strange and exotic beings." The stars chosen by Drake for the first SETI search were Tau Ceti in the Constellation Cetus (the Whale) and Epsilon Eridani in the Constellation Eridanus (the River), some eleven light years (66 trillion miles) away. Both stars are about the same age as our sun.
From April to July 1960, for six hours a day, Project Ozma's 85-foot NRAO radio telescope was tuned to the 21-centimeter emission (1420 MHz) coming from cold hydrogen gas in interstellar space. A single 100 Hz channel receiver scanned 400 kHz of bandwidth. The astronomers scanned the tapes for a repeated series of uniformly patterned pulses that would indicate an intelligent message or a series of prime numbers such as 1, 2, 3, 5 or 7. With the exception of an early false alarm caused by a secret military experiment, the only sound that came from the loudspeaker was static and no meaningful bumps superimposed themselves on the formless wiggles on the recording paper. After Project Ozma's pioneering steps, systematic searches for the technological manifestations of civilizations on the planets of other stars became a feasible scientific objective.