Seventy-two seconds in 1977, and nothing since
2026-04-20 · EA5IYR
On the night of 15 August 1977, a printout came off the Big Ear radio telescope at Ohio State. Nobody looked at it for three days.
When Jerry Ehman did, he circled six characters and wrote one word beside them: Wow! What the characters mean
Big Ear did not point at things. It had no motors worth the name; it stared at a fixed elevation and let the Earth's rotation drag the sky through its beam. Intensity was printed once every ten seconds as a single character — digits for weak, then letters as it climbed. U is the strongest thing the scale can express.
So 6EQUJ5 is not a message. It is a shape: a signal rising out of the noise, peaking at roughly thirty times the background, and falling away again. The detail that has kept it alive for fifty years
That rise and fall took 72 seconds, and 72 seconds is exactly how long a fixed point in the sky takes to cross Big Ear's beam.
That is the whole thing. Interference from the ground does not do that. An aircraft, a satellite in the wrong orbit, a microwave oven in the next county — none of them politely fade in and out on the precise schedule of the Earth's rotation. Whatever produced those characters behaved like something at astronomical distance.
It was also narrowband, close to 1420 MHz — the hydrogen line, the frequency SETI had spent two decades arguing anyone trying to be heard would choose. And then nothing
Ehman went back. Others went back, for decades, with better instruments. The same patch of Sagittarius has been watched repeatedly and it has never done it again.
That is the awkward part. A one-off detection is not evidence of anything; it is a detection you cannot check. The 2024 answer
In August 2024 a team working through archival Arecibo data proposed a mechanism that needs no one to be transmitting.
Space is full of cold hydrogen clouds. Hit one with a sudden hard burst of radiation — a magnetar flare, say — and you can stimulate the gas into emitting a brief, intense, narrowband pulse right at the hydrogen line. A natural maser: a microwave laser made of interstellar gas.
It would be narrowband. It would sit at 1420 MHz. It would appear once and never repeat, because the alignment of flare, cloud and telescope that produces it is vanishingly rare. Is that the end of it?
It is a hypothesis with a real mechanism behind it, which is more than the alternative has ever had. It has not been confirmed, and the original signal cannot be re-examined because there is nothing left to examine.
What the Wow! signal actually demonstrates is less romantic and more useful: how hard it is to say anything at all about an event that happened once. Every discipline that listens to the sky has learned the same lesson — an observation you can repeat tomorrow is worth more than a spectacular one you cannot.
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Sources: Universe Today — the Wow! signal deciphered, Astrobiology — Arecibo Wow! I, arXiv — Arecibo Wow! II, revised properties, EarthSky — new analysis closes in on the source.