On the night of 15 August 1977, Ohio State University’s “Big Ear” radio telescope was doing what it did every night: sweeping the sky for narrowband radio signals as part of a long-running SETI search. A few days later, volunteer astronomer Jerry Ehman sat down with the computer printout, ran his eye down columns of low numbers — and stopped.
One vertical string read 6EQUJ5: the telescope’s shorthand for a signal that rose to roughly thirty times the background noise and fell away again, tracing the exact shape you’d expect if a fixed point in the sky drifted through the telescope’s beam. It lasted 72 seconds — precisely as long as Big Ear’s field of view took to pass over any one spot. Ehman circled the sequence in red pen and wrote a single word in the margin: Wow!
Why it was such a good candidate
The signal arrived at almost exactly 1420 MHz — the emission frequency of neutral hydrogen, the most common element in the universe. SETI researchers had long argued that any civilisation trying to be noticed would broadcast near this “hydrogen line”, a frequency every radio astronomer in the galaxy would be watching. It was narrowband, unlike natural sources. And it came from the direction of the constellation Sagittarius, with no satellite, aircraft or ground transmitter ever convincingly matched to it.
The problem: it never came back
Big Ear pointed at the same patch of sky more than fifty times afterwards. Nothing. Later searches with more sensitive instruments, including the Very Large Array, also found nothing. Science has a hard rule about one-off events: a signal that can’t be re-observed can’t be confirmed, no matter how tantalising the printout.
Explanations have been proposed and mostly dismantled. A 2017 claim that a passing comet’s hydrogen cloud produced the signal was widely rejected by radio astronomers — comets don’t emit narrowband bursts like this. In 2022, amateur astronomer Alberto Caballero identified a Sun-like star in Sagittarius, catalogued as 2MASS 19281982-2640123, as a plausible origin worth targeting — a suggestion, not a solution.
The telescope is gone. The mystery isn’t.
Big Ear was demolished in 1998 to expand a golf course — an ending so bathetic it has become part of the legend. Ehman himself has remained carefully agnostic for nearly five decades, resisting both the alien conclusion and the debunkers’ shrugs.
Which leaves the Wow! signal exactly where it has always been: the single best unexplained candidate in the history of the search for extraterrestrial intelligence — 72 seconds long, heard once, by one telescope, on a summer night in Ohio.
