In 1977, a powerful 72-second radio signal from deep space was detected in Ohio. A scientist scrawled 'Wow!' on the printout, but the signal was never detected again.
August 15, 1977. 10:16 PM. The Big Ear radio telescope at Ohio State University locked onto something from the void of space.
The signal lasted just 72 seconds. But those 72 seconds would forever alter humanity's relationship with the cosmos.
Three days later, astronomer Jerry Ehman was reviewing the computer printout when an anomalous data string stopped him cold. "6EQUJ5"—an alphanumeric sequence representing a signal thirty times stronger than the background noise of deep space. Ehman circled the sequence in red ink and scrawled a single word in the margin.
"Wow!"
What made the Wow! Signal electrifying was not just its strength—it was its character.
The signal arrived at a frequency of 1420.4056 MHz, the precise emission line of neutral hydrogen—the most abundant element in the universe. In 1959, Cornell physicists Giuseppe Cocconi and Philip Morrison had predicted that any intelligent civilization attempting interstellar communication would likely broadcast at this exact frequency. It was, in effect, the universe's most logical "hailing channel."
The signal was narrowband, a characteristic virtually impossible to produce through known natural phenomena. It was as if someone had spoken in the universal language of physics.
But the deepest mystery is not the signal itself. It is that it never came again.
Ehman and astronomers around the world pointed the Big Ear and other telescopes at the same patch of sky. Hundreds of follow-up observations were conducted over the decades. The cosmos answered with nothing but silence.
The source of the signal has been estimated to lie in the direction of the constellation Sagittarius, roughly 220 light-years from Earth. Yet no known star system occupies that region of space.
In 2017, astronomer Antonio Paris of St. Petersburg College proposed an explanation. Two comets—266P/Christensen and 335P/Gibbs—were transiting the signal's region of sky in 1977. Paris suggested that the hydrogen cloud surrounding a comet could emit radiation at the 1420 MHz line.
The astronomy community was largely unconvinced. A comet generating a narrowband signal of such extraordinary intensity? The physics did not add up for most experts.
Nearly five decades later, the Wow! Signal remains the strongest candidate for an extraterrestrial radio transmission ever detected. It has never been explained, never been replicated, and never been heard again.
Somewhere in the direction of Sagittarius, in a region of sky where no known star shines, something produced a burst of energy on the one frequency that science predicted an alien civilization would choose. For 72 seconds, something—or someone—spoke.
We simply do not know what it said.
