On August 15, 1977, a radio telescope at Ohio State University picked up a signal from deep space. It lasted 72 seconds. It was so striking that the astronomer who reviewed the data circled it on the printout and wrote a single word in the margin: "Wow!"
That word became the signal's name. And nearly five decades later, the Wow! Signal remains the strongest candidate for extraterrestrial contact ever detected — and the only one that has never been explained away.
It has never been heard again.
The Big Ear telescope and SETI
In 1977, Ohio State University operated a radio telescope nicknamed "Big Ear" — a fixed, ground-based antenna that scanned the sky as the Earth rotated. It was part of SETI: the Search for Extraterrestrial Intelligence, a scientific program dedicated to detecting radio signals of non-natural origin from space.
The logic behind SETI was straightforward: if an intelligent civilization wanted to make itself known across interstellar distances, radio waves would be an efficient way to do it. Radio travels at the speed of light, penetrates space easily, and requires relatively simple technology to both produce and detect. If anyone out there was trying to be heard, radio was a reasonable place to listen.
Big Ear had been scanning for years without finding anything significant. Then, on the night of August 15, 1977, something changed.
What the signal looked like
The signal was discovered not in real time, but two days later when astronomer Jerry Ehman was reviewing printed data from the telescope's computer system. The data was printed as a sequence of letters and numbers representing signal intensity — standard background noise registered as low numbers and letters near the start of the alphabet.
What Ehman found in the August 15 data was a sequence that read: 6EQUJ5.
This wasn't noise. This was a signal that rose sharply in intensity, peaked, and fell — exactly the pattern you would expect from a fixed source in space passing through the telescope's field of view as the Earth rotated. The peak intensity, represented by the letter "U," was off the standard scale. It was, by a significant margin, the strongest narrowband signal Big Ear had ever recorded.
| Characteristic | What was observed | Significance |
|---|---|---|
| Frequency | 1420.456 MHz — extremely close to the hydrogen line | The hydrogen line (1420 MHz) is considered the most likely frequency for interstellar communication; it is a universal constant |
| Duration | 72 seconds | Exactly consistent with a fixed point source passing through Big Ear's beam as Earth rotates |
| Signal shape | Rose and fell in a smooth bell curve | Consistent with a distant point source; inconsistent with terrestrial interference, which would be irregular |
| Bandwidth | Narrowband — less than 10 kHz wide | Known natural sources do not produce narrowband signals at this frequency; narrowband is a signature of artificial transmission |
| Origin | Direction of the constellation Sagittarius | No known star or object at that location has been identified as a plausible source |
Why it matters — and why it's so frustrating
The Wow! Signal ticks almost every box that SETI researchers had defined as indicators of a potentially artificial extraterrestrial signal. It came from the right direction. It was at the right frequency. It had the right shape. It was far stronger than anything else ever recorded.
And then it stopped. And it never came back.
Dozens of attempts have been made to redetect it — by Big Ear itself, before it was demolished in 1998, and by other telescopes since. None have succeeded. The sky at those coordinates has been searched repeatedly, at the right frequency, with increasingly sensitive equipment. Nothing.
This is the central frustration of the Wow! Signal: it is simultaneously the best evidence we have ever found for a non-natural extraterrestrial radio source, and completely useless as evidence because it cannot be confirmed.
The alternative explanations
| Explanation | Core argument | Why it's contested |
|---|---|---|
| Interstellar scintillation | A known but faint signal was temporarily amplified by interstellar gas clouds, making it appear stronger than it is | Would not produce the specific frequency, shape, and bandwidth characteristics observed |
| Cometary hydrogen cloud | A 2016 study proposed that two comets passing through the area at the time could have produced a hydrogen emission at 1420 MHz | The hypothesis was widely criticized; the comets' known positions don't precisely align, and the signal characteristics don't fully match cometary emission profiles |
| Classified satellite transmission | A military or classified satellite produced the signal | The signal came from a direction inconsistent with Earth orbit; satellites would also produce a different signal shape |
| Radio frequency interference | Terrestrial interference was mistakenly recorded as a space signal | The signal's shape is inconsistent with terrestrial sources, which don't produce the smooth rise-and-fall pattern of a fixed space source |
Jerry Ehman's own position
Jerry Ehman, the astronomer who first identified the signal and wrote "Wow!" in the margin, has been careful and precise in his public statements about it for decades. He has said repeatedly that he does not know what caused it. He has also said, with equal care, that he does not believe it has been adequately explained by any of the natural or terrestrial hypotheses proposed so far.
In a 1994 paper, he wrote: "We should not jump to conclusions… but we cannot exclude the possibility that this was a signal of extraterrestrial intelligent origin."
That remains, essentially, the scientific consensus: unknown, unexplained, and unresolved.
The curious connection
The Wow! Signal raises a question that goes beyond astronomy: what would it actually mean for humanity if we confirmed we were not alone?
Psychologists and sociologists who study this question — and it is a genuine field of research, sometimes called "astrosociology" — have found that the answer is more complicated than either the optimistic or catastrophic scenarios typically portrayed in science fiction.
Studies consistently show that most people, when asked directly, say they believe extraterrestrial life probably exists and that confirmation would not significantly disturb their worldview. But the same studies show that institutions — religious organizations, governments, financial markets — are far less prepared for such a confirmation than individuals.
The 72 seconds of the Wow! Signal were not enough to change anything. But they were enough to pose the question seriously, in a way that no amount of theoretical discussion had managed before. Something, somewhere, may have been transmitting. We heard it once. We have been listening for it ever since.
FAQ
What was the Wow! Signal?
The Wow! Signal was a strong narrowband radio signal detected on August 15, 1977, by the Big Ear telescope at Ohio State University. It lasted 72 seconds, originated from the direction of the constellation Sagittarius, and bore the characteristics expected of an artificial extraterrestrial transmission. It has never been detected again.
Why is it called the Wow! Signal?
Astronomer Jerry Ehman wrote the word "Wow!" next to the data printout when he reviewed it two days after the signal was recorded. The name stuck and has been used ever since.
Has the Wow! Signal ever been detected again?
No. Despite numerous attempts using increasingly sensitive equipment, the signal has never been redetected. This non-repeatability is the primary reason it remains unconfirmed as evidence of extraterrestrial intelligence.
What frequency was the Wow! Signal on?
The signal was detected at approximately 1420.456 MHz, very close to the hydrogen line at 1420.405 MHz. The hydrogen line is considered by SETI researchers to be the most likely frequency for intentional interstellar communication because hydrogen is the most common element in the universe.
Where did the Wow! Signal come from?
The signal appeared to originate from the direction of the constellation Sagittarius, approximately 2.5 degrees south of the fifth-magnitude star Chi Sagittarii. No known star or object at that precise location has been identified as a plausible natural source.