SETI is a scientific project using large telescopes in the search for extra-terrestrial intelligence. On August 15, 1977 the Ohio State Radio Observatory detected the most promising extraterrestrial candidate signal to date. The so-called "Wow!" signal received its name from the note written in the margin of the computer printout by Dr. Jerry Ehman. The signal rises about 15 dB above the mean background noise, in a single channel.

An analysis of the Wow! signal indicates that its source was moving with the background stars. From its Doppler shift signature, terrestrial interference, aircraft, and spacecraft can be ruled out as possible origins of the signal. The antenna coordinates indicated that the signal was coming from no known nearby solar-type stars. The only condition required for a SETI signal not met was that of repeatability. However, since the Ohio State Big Ear radiotelescope has an extremely narror beamwidth, viewing just one part in a million of the sky at any given time, one would not expect the signal to repeat. Assuming the Wow! signal is a typical SETI-like transmission, then we can expect valid SETI hits to be very strong, high intermittent signals which appear once (as the transit beam sweeps past Earth), and never repeat again. Unless the signal is detected again, we may never know for sure.