Wow Signal: The 72-Second Transmission From Deep Space That Scientists Still Can't Explain — 49 Years On

For exactly 72 seconds in August 1977, a radio telescope in rural Ohio picked up something it had never heard before. The signal was loud, narrow, and perfectly tuned to the one frequency astronomers had pre-selected as the most likely channel for alien communication. Then it stopped. Nobody has heard it since.

The astronomer who noticed it — a research associate named Jerry Ehman — looked at the printout weeks later and drew a circle around the data. Then he wrote one word in the margin.

Wow!

Forty-nine years later, that scrawled notation is still the most famous anomaly in the history of the search for extraterrestrial intelligence. And nobody has a fully satisfying explanation for what caused it.

What exactly was the Wow Signal?

The Wow Signal was a strong, narrowband radio transmission detected on August 15, 1977 by the Big Ear Radio Observatory at Ohio State University. Big Ear was part of a SETI project — systematically scanning the sky for unusual radio emissions. Most of what it found was unremarkable background noise. The Wow Signal was not that.

The signal arrived at 1420.356 MHz — almost exactly the emission frequency of neutral hydrogen, the most abundant element in the universe. SETI scientists had specifically flagged this as the likeliest frequency for any civilization trying to make contact. It's the cosmic equivalent of broadcasting on Channel 1. Any sufficiently advanced species would know that number.

Second: the signal was roughly 30 times stronger than background noise. Third, and most importantly — it behaved exactly as a signal from a fixed point in deep space should behave as Earth's rotation slowly swept the telescope's beam across it. It rose, peaked, and fell in a perfect bell curve across the full 72-second window.

Why do scientists think it could be alien?

The hydrogen line isn't just a frequency. It's a statement. Any civilisation advanced enough to build a transmitter probably understands that hydrogen is the most common atom in the cosmos. Broadcasting at 1420 MHz is like leaving a message that says: whoever finds this, you know this number. It's a shared reference point written into the fabric of physics itself.

That string is what Big Ear's printout actually showed. The telescope didn't record audio — it printed intensity values as numbers and letters, with higher letters indicating stronger signals. The 'U' at the peak was extraordinary. Ehman circled the whole sequence in red on September 18, 1977, a month after the signal arrived. That original printout still exists, in an Ohio State University archive. The ink is still legible.

The signal also came from the direction of the constellation Sagittarius — roughly toward the galactic centre, a region packed with hundreds of billions of stars. It showed none of the telltale signatures of known human-made radio frequency interference. It was detected on a single receiver, which is actually consistent with a signal sweeping across a narrow beam from a fixed point in deep space.

Has the Wow Signal been explained?

Not definitively. No. That is the honest answer, and scientists deserve credit for saying so.

In 2017, astronomer Antonio Paris proposed that the signal came from a hydrogen cloud surrounding a passing comet — specifically 266P/Christensen or P/2008 Y2 Gibbs, which were crossing that area of sky in August 1977. The hypothesis received significant media attention. However, Ehman himself and multiple SETI researchers pushed back hard: Big Ear had observed that sky region dozens of times with comets present, and nothing remotely similar was ever detected. The comet hypothesis remains deeply contested within the field and is not considered settled.

Other proposed explanations — terrestrial interference, a satellite reflection, atmospheric distortion — have all been examined and largely set aside. The signal's properties simply do not match any known natural or human-made source convincingly enough to close the case.

Why haven't we found it again?

Big Ear itself was demolished in 1998. To make way for a golf course. Not a metaphor. An actual golf course sits where the most anomalous SETI detection in history was made — a signal recorded on a system that printed its findings on paper, at a telescope that no longer exists.

The search has continued with far more powerful instruments. The Allen Telescope Array in California. The Parkes Observatory in Australia. Breakthrough Listen — a $100 million privately-funded SETI program backed by Yuri Milner and publicly championed by Stephen Hawking before his death — has surveyed over a million stars and 100 galaxies. The relevant area of Sagittarius has been scanned repeatedly. Nothing matching the Wow Signal's profile has appeared.

Which means one of three things. It was a one-time natural event we haven't correctly identified. It was a deliberate, directed transmission that moved on. Or it was something else entirely — a category of phenomenon we don't have a name for yet. The SkyLens learn section walks through how radio astronomy and SETI searches actually work, if you want to understand the mechanics of what we're listening for.

What happens if we actually detect it again?

There's a formal protocol for exactly this scenario. The SETI Institute's Declaration of Principles Concerning Activities Following the Detection of Extraterrestrial Intelligence lays out the steps: verify independently with a second telescope, notify the scientific community — not a government — and do not respond without international consensus.

That last part is genuinely contested. Some researchers argue we should transmit back immediately. Hawking was in the opposite camp: he spent years warning that drawing attention to ourselves could be among the most dangerous decisions humanity ever makes. His reasoning — that any civilisation advanced enough to receive our signal is advanced enough to do us harm — remains a live debate in astrobiology and geopolitics alike.

The signal came from somewhere in the direction of the galactic centre, where star density is high enough that statistically, tens of millions of potentially habitable worlds may exist. If something there sent the Wow Signal, it did so when Jimmy Carter was US President, the first Star Wars film had just opened in cinemas, and the word 'internet' hadn't been coined yet. The signal has been travelling for at least as long as we've been looking for it. Possibly much longer.

Somewhere in an Ohio State University archive, a printout sits in a folder. There is a red circle around six characters. There is a word written in the margin in ballpoint pen. Scientists have spent nearly five decades trying to explain that word away. They haven't managed it yet.

The SkyLens live tracker shows you every object currently in Earth's orbit — 16,000 satellites, debris fields, everything humanity has put up there. The Wow Signal came from somewhere far beyond all of it. Wherever that is, we're still listening.