The Wow! Signal: A Strong Narrowband Radio Detection from 1977 Remains Unexplained

Detection of the Wow! Signal

On August 15, 1977, the Big Ear radio telescope at Ohio State University, which was engaged in the search for extraterrestrial intelligence (SETI), detected a powerful narrowband radio signal. The signal originated from the direction of the constellation Sagittarius and exhibited characteristics consistent with an extraterrestrial source.

Discovery and Naming

Volunteer astronomer Jerry R. Ehman identified the signal days later while reviewing computer printouts of recorded data. He circled the intensity reading "6EQUJ5" and wrote "Wow!" next to it, giving the event its widely recognized name. The signal sequence was observed for the full 72-second duration that Big Ear could monitor it.

Lack of Recurrence and Explanation

Despite numerous subsequent searches and various hypotheses, including reflections from space debris or comet hydrogen clouds, the Wow! signal has never been detected again. No terrestrial or extraterrestrial explanation for its origin has been confirmed. The single occurrence and inability to replicate the signal limit the strength of any interpretation, including the possibility of an extraterrestrial transmission.

Background of SETI and Signal Expectations

The Big Ear radio telescope was dedicated to SETI in 1973, following an extensive survey of extragalactic radio sources. This program became the longest-running of its kind. The search was partly inspired by a 1959 paper by Cornell University physicists Philip Morrison and Giuseppe Cocconi, who theorized that extraterrestrial civilizations might communicate using the 21-centimeter spectral line frequency of hydrogen, a common element in the universe.