In 1960, radio astronomer Frank D. Drake, then at the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia, carried out humanity's first modern 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), each being approximately eleven light-years (64 trillion miles) away. Both stars are about the same brightness as the Sun, and were assumed (but not known at the time) to have planets. While Tau Ceti is a bit older than the Sun, Epsilon Eridani is substantially younger.
From April to July 1960, for six hours a day, the receiver on the 85-foot antenna was tuned to the frequency of the 21-centimeter emission line of interstellar hydrogen. The assumption was that this frequency, 1420 MHz, would be known by any technologically sophisticated society, and would constitute a universal “hailing frequency.” A single 100 Hz channel receiver was slowly tuned up and down the dial to cover 400 kHz.
Drake deliberately used existing receivers and other technology for Ozma, not wishing to invite criticism by spending a great deal of money on an experiment that some might consider frivolous. The total cost of the project was about two thousand dollars.
The small Ozma team used a chart recorder and a loudspeaker to monitor any signal coming into the antenna. With the exception of an early false alarm probably caused by aircraft radar, the only sound that came from the loudspeaker was static, and no meaningful bumps superimposed themselves on the wiggles traced out on the chart recorder.
After this pioneering experiment, other searches for signals from the directions of other stars were conducted. Within a year, the first scientific meeting to discuss the prospects of a search was held in Green Bank, during which the Drake Equation was introduced.
The era of SETI had dawned.
-Seth Shostak, updated: July 2021.