The Wow! Signal: The Most Compelling Evidence for Extraterrestrial Intelligence Ever Recorded — and It Lasted 72 Seconds
On 15 August 1977, a radio telescope in Ohio detected a signal so anomalous that the astronomer monitoring the data wrote 'Wow!' in the margin. It has never been detected again.
On the night of 15 August 1977, the Big Ear radio telescope at Ohio State University was conducting a routine sky survey as part of the SETI programme — the Search for Extraterrestrial Intelligence. The telescope was unmanned; it recorded data on computer printouts that were reviewed by researchers the following day. When astronomer Jerry Ehman reviewed the printout from that night, he circled a sequence of characters and wrote a single word in the margin: 'Wow!'
The signal lasted 72 seconds — the full duration of Big Ear's observation window as the Earth rotated. It appeared at 1420 MHz, the frequency of hydrogen, which SETI researchers had long identified as the most likely frequency for an intentional interstellar transmission: hydrogen is the most abundant element in the universe, and any technologically advanced civilisation would know that any other civilisation would be monitoring it.
The signal's characteristics were extraordinary. Its intensity rose and fell in exactly the pattern expected from a point source in deep space passing through the telescope's beam as the Earth rotated. It showed no signs of Doppler drift from a moving source within the solar system. It was narrowband — confined to a very tight frequency range — which is inconsistent with natural astrophysical sources, which tend to emit across broad frequency ranges.
In the forty-nine years since the Wow! signal was detected, it has never been observed again. Big Ear monitored the same region of sky for years afterwards. Other radio telescopes have searched the same coordinates. Nothing has been found. The signal appeared once, for 72 seconds, and then was gone.
Several natural explanations have been proposed over the years. In 2017, a team of researchers suggested the signal could have been caused by a comet passing through the field of view, with hydrogen gas from the comet's coma producing the observed frequency. The hypothesis was contested by other researchers, who pointed out that the signal's characteristics were inconsistent with a cometary source.
The Wow! signal remains officially unexplained. It is not proof of extraterrestrial intelligence. It is not proof of anything. It is a single data point — 72 seconds of anomalous radio emission from an unidentified source — that has resisted every explanation offered for it over nearly five decades. That is either very interesting or very frustrating, depending on your disposition. Possibly both.