The Wow! Signal: The 72-Second Mystery That Still Haunts Astronomy

On August 15, 1977, at 11:16 PM Eastern time, the Big Ear radio telescope at Ohio State University was doing what it always did: scanning the sky for signs of extraterrestrial intelligence. Nothing unusual had happened in years. The project was famously underfunded — the telescope was built from spare car parts and cyclone fencing — and the data came out as green computer paper printouts, page after page of numbers and letters.

But that night, one page was different.

The Printout

A volunteer astronomer named Jerry Ehman was reviewing the data when his eye caught a sequence on one particular printout. The telescope scanned the sky by letting the Earth's rotation sweep it across fixed points, so signals appeared as a rising and falling intensity over about 72 seconds. The code used letters to represent signal strength: 1-9 for weak, A-Z for strong. What Ehman saw was a sequence reading:

6EQUJ5

Today, that string is one of the most famous artifacts in SETI history. The intensity rose rapidly to a peak of "U" (about 30 times the background noise), then fell away symmetrically — exactly what you'd expect from a signal of artificial origin coming from a point source.

Ehman circled the sequence and wrote a single word in the margin:

Wow!

Why It Still Matters

The signal checked every box for a potential alien transmission — and it still does. Here's what made it so compelling:

Narrowband frequency. The signal was at 1420 MHz, which is the radio emission frequency of neutral hydrogen — a frequency that any technologically advanced civilization would recognize as significant. SETI scientists have long considered this the "water hole" frequency, a natural meeting point for interstellar communication. It's protected by international treaty, in fact: no human transmitters are allowed to broadcast at 1420 MHz.

Point source. The signal came from a single, fixed point in the sky. It wasn't scattered ground interference or a passing satellite. The telescope's twin feed horns confirmed it — the signal appeared first in one horn, then 72 seconds later in the second, exactly as a celestial source would.

No human explanation fits. Every proposed explanation has been tested and failed. It wasn't a satellite — none existed in that orbit at that frequency. It wasn't a military aircraft or secret test — classified records have been checked. It wasn't an Earth-based reflection — the signal's pattern was too clean. It wasn't the radio source of a known star or planet — nothing nearby produces signals like that.

The most frustrating part? Big Ear had only one data channel, so it couldn't record phase or polarization information. And because the telescope's design swept fixed points in the sky, the signal was only visible for 72 seconds before the Earth rotated past the source. By the time Ehman saw the printout, it was too late.

The Many Attempts to Find It Again

Scientists have pointed radio telescopes at the signal's coordinates — in the constellation Sagittarius, near the star group Chi Sagittarii — dozens of times since 1977. The Very Large Array, the Arecibo Observatory (before its collapse), and the Allen Telescope Array have all searched. Nothing. Not a peep.

The silence is itself a clue. If the signal was a natural astrophysical phenomenon, we'd expect it to repeat. Natural sources like pulsars, quasars, and masers emit regularly. The Wow! Signal appeared exactly once and never returned. That makes it either:

• A one-time artificial transmission (a beacon that fired once)
• A natural event we've never seen before or since
• Scatter from an Earth-based source so weird that we can't identify it after 50 years of trying

None of these are satisfying — which is exactly why the mystery persists.

The Best Theories (and Their Problems)

1990s: The Hydrogen Cloud Hypothesis. In 1994, astronomer Antonio Paris proposed that the signal could have been caused by a hydrogen cloud excited by a passing star or comet. The idea gained traction but was largely disproven when the comet theory predicted specific characteristics that didn't match the signal's behavior.

2000s: The Galactic Maser Idea. Some suggested a natural maser (laser-like microwave emission) from excited gas clouds. But masers are broadband — the Wow! Signal was extremely narrowband. Masers also tend to drift in frequency due to Doppler effects. The Wow! Signal stayed locked at exactly 1420 MHz.

2010s: The Starlink Problem. The rise of satellite constellations has created new interference sources that sometimes mimic narrowband signals. But the Wow! Signal predates our satellite-choked skies by decades.

2020s: AI to the Rescue. In 2022, a group of researchers applied machine learning to archival Big Ear data, looking for weaker signals that might have been missed. They found eight new potential signals of interest — but none that matched the Wow! Signal's potency or profile.

The Man Who Found It

Jerry Ehman never became a household name, and he was fine with that. He continued working in radio astronomy and SETI for decades, always cautious not to overstate what the signal meant. "We should have re-observed it," he said in a 2007 interview. "But hindsight is always 20/20."

Before his death in 2024, Ehman reflected on the mystery: "I'd like to think it was something extraordinary. But I'd also like to know what it was. Not knowing is the hard part."

Where We Stand Today

The Wow! Signal's coordinates are known: RA 19h25m31s ± 10s, Dec -26°57' ± 20'. The region contains no stars within 1,000 light-years that resemble our Sun. But it does contain something interesting: a red dwarf star system called 2MASS 1925-2657, about 1,200 light-years away.

In 2024, the Green Bank Telescope spent 28 hours listening to the Wow! Signal's patch of sky at high resolution. The data is still being analyzed. New techniques in signal processing and machine learning are being applied to the original 1977 data for the umpteenth time.

So far, the universe is still keeping its secret.

What You Can Do

The Big Ear data is in the public domain. Citizen scientists and amateur astronomers regularly analyze the signal on platforms like SETI@home (though the project went into hibernation in 2020). The Allen Telescope Array occasionally targets the coordinates during its observation cycles.

Want to try your own analysis? The raw 1977 printout is available online. Some researchers believe there might be clues hidden in the data that 1970s computers simply didn't have the resolution to see.

Further Reading

• Robert H. Gray, The Elusive Wow: Searching for Extraterrestrial Intelligence (2012)
• SETI Institute's ongoing Wow! Signal research page
• The Big Ear Radio Observatory memorial site

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One signal, 72 seconds, fifty years of uncertainty. Whether it was a message from another civilization or a cosmic prank we'll never understand, the Wow! Signal is a reminder of how much we still don't know — and how thrilling that can be.