The Signal Nobody Can Explain
September 5, 2026 · by White Nights
On August 15, 1977, astronomer Jerry Ehman was reviewing data from the Big Ear radio telescope at Ohio State University when he noticed something. A signal had been detected six days earlier that matched, almost perfectly, what SETI researchers would expect from a transmission originating from an extraterrestrial intelligence. It was narrowband, coming from the direction of the constellation Sagittarius, at the precise frequency of 1420 megahertz — the emission frequency of neutral hydrogen, which scientists had theorised would be a universal calling card for any technologically sophisticated civilisation.
Ehman circled it in red pen on the printout and wrote "Wow!" in the margin. That's how it became known as the Wow! Signal.
It lasted 72 seconds — the full amount of time the telescope could track a fixed point in the sky as the Earth rotated. It has never been detected again, despite subsequent attempts using the same and more powerful equipment. What caused it is unknown. Natural astrophysical explanations have been proposed and largely ruled out. The hydrogen emission frequency is protected from human broadcasting by international agreement, so terrestrial interference is unlikely. In 2016, a team proposed it might have been caused by a hydrogen cloud surrounding a comet — but other researchers pushed back.
Forty-eight years later, the Wow! Signal remains unexplained and unrepeated. The data is still there, in a printout in a filing cabinet, with Jerry Ehman's handwriting in the margin.