On the night of August 15, 1977, astronomers working with the Ohio State University’s famed Big Ear radio telescope recorded something extraordinary — a fleeting, narrow-band radio burst that bore all the hallmarks of a signal from deep space. The reading “6EQUJ5” leapt off a printout, inspiring volunteer astronomer Jerry R. Ehman to circle it in red and write beside it “Wow!” — and so a legend was born.
Here’s what we know — and what still puzzles us.
What happened
The Big Ear telescope was scanning the sky near the 21-centimetre hydrogen line at about 1420 MHz, a frequency long considered promising in the search for extraterrestrial intelligence (SETI). At around 23:16 EDT (03:16 UTC) that evening, the system registered a signal of unprecedented strength: a sequence of alphanumeric characters printed on paper, “6EQUJ5”.
The profile of the signal was compelling: it lasted the full 72 seconds that Big Ear could observe that patch of sky (because the telescope used the Earth’s rotation rather than tracking). The intensity rose, peaked, and fell in a way consistent with what one would expect from a fixed cosmic source drifting through the antenna beam.
Yet, despite many follow-up observations — by the Big Ear team and later by other instruments — the signal was never detected again.
Why it mattered
Because of how clean, strong and short-lived it was, the “Wow!” signal became perhaps the most intriguing candidate ever recorded in SETI research. A narrow-band burst at the hydrogen line is precisely what one might expect if an extraterrestrial civilisation deliberately chose that frequency. That alone stirred the imagination.
But of course, the excitement comes with caveats: one-off events are extremely hard to interpret. The lack of repeat detection means we have no way to confirm if it was artificial (i.e., deliberate) or natural (or even terrestrial interference).
Possible explanations
Over the decades, many hypotheses have been floated — here are some of the leading ideas:
Terrestrial interference or reflection: Some experts have suggested the signal might have been a human-made transmission reflected off space debris or other objects. Even the original discoverer, Jerry Ehman, later acknowledged this as a possibility.
Cometary hydrogen cloud: In 2016, researcher Antonio Paris proposed that two comets (266P/Christensen and P/2008 Y2 Gibbs) passing through the region might have carried large hydrogen clouds emitting at that frequency. But the idea has been disputed by others because the timing and beam direction don’t line up convincingly.
Natural astrophysical event (maser/flare): More recently, studies suggest the signal may have been caused by a natural outburst — for example, a flare from a magnetar or other compact object hitting a hydrogen cloud, creating a brief maser-like burst of radio waves. A paper published in 2024 and 2025 refines this hypothesis.
Why it’s still unresolved
Despite the intriguing clues, none of the proposed explanations fully satisfies all the observations.
If it were a terrestrial reflection, the beam pattern and narrow-band nature still seem odd.
If it were a cometary hydrogen cloud, the geometry and intensity remain hard to reconcile.
If it were a natural maser or astrophysical flare, the rarity and lack of repetition keep it in the “possible but unproven” category.
Recent work has narrowed down its possible location in the sky and adjusted the measured frequency slightly, raising the probability of an astrophysical rather than human origin — yet still no definitive proof.
Why it matters for SETI and science
The “Wow!” signal remains a powerful reminder of both the promise and the challenge of SETI. On one hand, it shows that our instruments can pick up signals that look very much like what we’d expect from an alien source (if such existed). On the other hand, it highlights the crucial issue: repeatability. Without repeated detection or independent confirmation, interpretation remains speculative.
It also underscores the need for better instrumentation, broad-sky coverage, and continuous monitoring — because cosmic phenomena don’t always repeat neatly. Moreover, the signal has prompted scientists to widen the kinds of phenomena they consider “technosignatures” (i.e., not only deliberate alien beacons but also unusual natural astrophysical events).
The 72-second “Wow!” signal picked up by the Big Ear telescope on August 15, 1977 remains one of astronomy’s most alluring mysteries. Whether it was a message from beyond, a quirk of our own hardware, or a once-in-a-cosmic-lifetime natural flare, we don’t yet know. What we do know is that it happened, it was unexpected, and nearly half a century later, scientists are still talking about it.
And perhaps that’s fitting: if we truly seek to answer the question “Are we alone?”, then the signal that made astronomer Jerry Ehman scrawl “Wow!” may be our most tantalising clue at least so far.