72 Seconds from Sagittarius: The Signal That Made an Astronomer Write "Wow!"
In August 1977, the Big Ear radio telescope at Ohio State University was doing what it did every night: silently sweeping the sky in search of extraterrestrial intelligence. Nobody listened in real time; the data simply piled up as columns of numbers on computer printouts. A few days later, volunteer astronomer Jerry Ehman sat down to review the sheets — and froze. There, among the low routine values, stood a vertical burst of code: 6EQUJ5. He circled it in red ink and wrote a single word in the margin: "Wow!"
The strange sequence was not a message. It was Big Ear's way of recording intensity, and it described a signal roughly thirty times stronger than the background noise of space. Detected on August 15, 1977, it was narrowband — concentrated near 1420 megahertz, the emission frequency of neutral hydrogen, the very channel SETI pioneers had predicted an alien civilization would choose, because every radio astronomer in the galaxy would know it. And it came from the direction of the constellation Sagittarius, toward the heart of the Milky Way.
The most haunting detail was its duration: 72 seconds. Big Ear was a fixed telescope; Earth's rotation carried its beam across the sky, so any genuine celestial source would drift through it in exactly 72 seconds, growing louder and then fading in a smooth curve. The Wow! signal did precisely that. Local interference almost never behaves so perfectly.
Then it vanished. Ehman and his colleagues pointed Big Ear at the same patch of sky for weeks. Astronomer Robert Gray hunted the signal for decades, using the Very Large Array in New Mexico and a telescope in Tasmania. Dozens of follow-up observations found nothing. A true beacon, many argued, should repeat. This one never did.
Explanations have come and gone. Ehman himself wondered whether a stray earthly transmission had bounced off space debris. In 2017, one researcher blamed hydrogen clouds around a pair of passing comets — a claim most astronomers swiftly rejected, noting the comets were too faint and not in the right place. In 2024, a team led by astrobiologist Abel Méndez proposed something stranger: a rare flare from a magnetar may have lit up a cold interstellar hydrogen cloud, producing a natural maser-like burst. Intriguing — but none of these hypotheses has been confirmed.
Big Ear itself is gone, demolished in 1998 to make way for a golf course. What remains is a yellowed printout, six circled characters, and the questions that refuse to die: What sent the signal? Why exactly on the hydrogen line? And why, in nearly half a century of listening, has the sky never said it again?