There was nothing unusual about the night of August 15, 1977. Somewhere in Delaware, Ohio, the enormous Big Ear radio telescope was quietly scanning the sky. Its job was to listen. The telescope wasn’t taking any photographs. It wasn’t looking for strange lights or distant planets. It was listening for radio waves coming from the universe. The signals that might reveal something about the cosmos. Most of what it detected was ordinary. Then, buried inside the data, something appeared that made one astronomer stop.
It was simply a powerful radio signal that had arrived from the sky, lasted for roughly 72 seconds, and then disappeared. When astronomer Jerry Ehman later examined the computer printout, he noticed a peculiar sequence of characters:
6EQUJ5
It represented the changing strength of the signal. Ehman circled the sequence in red and wrote a single word beside it:
“Wow!”
He had no idea that those few seconds would become one of the most enduring mysteries in the search for extraterrestrial intelligence.
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The Night the Big Ear Heard Something Different
The Big Ear telescope belonged to Ohio State University’s Radio Observatory and had been involved in SETI—the Search for Extraterrestrial Intelligence. The idea behind SETI was fascinating but straightforward. If intelligent civilizations existed elsewhere, perhaps some of them might produce detectable radio signals. The Big Ear continuously scanned the heavens, recording radio emissions and converting them into data that researchers could later examine.
On that August evening, the telescope was pointed toward a region of the sky near the constellation Sagittarius. As Earth rotated, the telescope’s field of view slowly moved across the sky. And then something unusual passed through it. The signal didn’t simply appear at full strength. Its intensity gradually increased, then gradually faded.
Source: Wow! Signal: Origin of possible alien signal narrowed down – study
The 72 Seconds
The entire event lasted approximately 72 seconds. A stationary radio source in space passing through the telescope’s beam as Earth rotated could produce a characteristic rise-and-fall pattern. And that’s roughly what happened. The signal grew stronger, then it reached its peak. And finally, it was gone. The telescope continued listening, but the signal wasn’t there.
What was The Wow! Signal?
To someone looking at the original printout, 6EQUJ5 might have looked like a strange code. The characters represented measurements of the signal’s intensity over successive time intervals. The sequence showed that the signal became dramatically stronger than the normal background noise before fading again. The letter U, for example, represented an especially high intensity level. This was one of the reasons Ehman immediately recognized that the event was extraordinary. The signal appeared to have characteristics that made ordinary local interference less obvious as an explanation. It seemed to be coming from the sky.
Where Did It Come From?
The signal appeared to originate from a region of the sky toward Sagittarius. Astronomers could determine the approximate region of the sky from which the signal arrived, but they could not identify a specific star, planet, spacecraft, or object as its source. The telescope’s design also meant that the exact position could not be pinpointed with modern precision. So scientists were left with a broad cosmic neighborhood but no obvious culprit. If the Wow! Signal had been detected repeatedly, astronomers could have studied it. They could have compared observations, searched for patterns, or attempted to determine its origin. Instead, the event became a one-time mystery.
Could It Have Been Aliens?
This is the theory that made the Wow! Signal famous. The possibility of an extraterrestrial origin was immediately intriguing. The signal was unusually strong. It was concentrated within a relatively narrow radio frequency range, and it occurred close to the hydrogen line, around 1420 MHz. Hydrogen is the most abundant element in the universe, making the hydrogen line particularly significant to radio astronomers. Some scientists have argued that this frequency would make a logical choice for an intentional interstellar communication.
However, there is no evidence proving that the Wow! Signal was an alien transmission since there was no repeating message. There was no independent observation confirming that an extraterrestrial civilization produced it. So while an extraterrestrial explanation remains fascinating, it remains speculation. Despite the excitement surrounding his discovery, Ehman himself was cautious. He understood that an extraordinary signal needed an extraordinary level of verification, and a single observation wasn’t enough. If the signal had been detected again under similar circumstances, the scientific case would have become much stronger. Instead, there was silence.
A Natural Phenomenon
Over the years, researchers have proposed various astronomical explanations. One possibility is that the signal came from an unusual natural astronomical event. More recently, researchers have explored the idea that a transient event involving hydrogen clouds and energetic radiation might have temporarily produced a powerful radio emission. Other possible astronomical sources have also been considered. But again, a good scientific explanation needs to account not only for what happened but also for why it happened only once.
The Comet Theory
One of the more controversial explanations involved comets. A 2017 study suggested that a hydrogen cloud surrounding a comet might have produced the signal. Two comets, 266P/Christensen and P/2008 Y2 (Gibbs), were proposed as possible candidates. The theory attracted attention because it offered a potential natural explanation for the mysterious radio burst. But it was also heavily debated. Critics questioned whether the proposed comets could realistically produce a signal with the observed characteristics. Later, observations did not provide a definitive resolution.
Could It Have Been Human Interference?
Another possibility is that the signal originated on Earth. Radio telescopes can detect human-made transmissions, satellites, spacecraft, and other forms of interference. However, researchers have found the Wow! Signal particularly difficult to explain as ordinary interference because of its characteristics and apparent direction. That doesn’t particularly mean terrestrial interference has been completely ruled out. It simply means that no confirmed human source has been identified.
The Signal That Never Came Back
Perhaps somewhere in the cosmos, a rare astronomical event briefly produced a burst of radio energy that happened to cross the Big Ear telescope’s path. Or perhaps, somewhere unimaginably far away, another civilization once transmitted a signal that happened to cross our corner of the universe for only 72 seconds. And after nearly five decades, the most famous signal in SETI history remains exactly what it was when Jerry Ehman first saw those six characters on the printout: A signal without an answer.
