On August 15, 1977, at 10:16 p.m., Jerry Ehman was reviewing computer printouts from the Big Ear Radio Observatory in Delaware, Ohio, performing volunteer work for a SETI project. He was looking at data from the previous night's observations—the usual scans of the sky, searching for narrowband radio signals that might indicate transmissions from elsewhere. What he found, printed across the paper in a sequence of numbers and letters, was the most anomalous signal in the history of SETI detection.
The signal appeared in the narrow band of 1420 megahertz—the hydrogen line, the frequency that most naturally carries astrophysical information and the frequency that scientists reasoned an extraterrestrial civilisation might choose for interstellar communication. Its strength was extraordinary: six times the background noise level. It lasted for 72 seconds—the exact duration it would take the Earth's rotation to sweep such a narrow-beam observatory across a point in the sky. And it appeared at only one location on the printout, confirming that it had come from a specific celestial position in the Chi Sagittarii star group. Everything about it was anomalous. Everything about it was, in a word, "Wow!"
That word—hand-written in red ink in the margin of the printout—became the signal's permanent name.
The Discovery and Its Aftermath
Ehman worked as a professor of electrical engineering while volunteering with the Ohio State University Radio Observatory SETI project. The Big Ear was not designed to detect extraterrestrial signals; it was designed to conduct a survey of the radio sky. But it was sensitive and careful in its methodology, making it an ideal platform for signal detection. The SETI volunteers, Ehman among them, understood their task: identify anomalies, report them, and avoid jumping to conclusions.
When Ehman circled the 6EQUJ5 data—where the "6" represented a signal strength six times background noise—he knew he was looking at something unusual. But he did not know what it was. He immediately contacted other team members, particularly Krzysztof Borkowski, a fellow volunteer. They discussed possibilities: instrumentation error? Interference from Earth? A natural astrophysical phenomenon? An artificial signal?
What followed, over the subsequent decades, was a case study in scientific restraint. Ehman became one of the most outspoken advocates for caution in interpreting the Wow! Signal. He published detailed analyses of the observation. He examined the evidence for natural explanations—radio emissions from known solar system objects, reflections from satellites, terrestrial interference. Over and over, in lectures and papers, he reiterated a crucial point: one detection is not enough. A genuine SETI signal would need to be confirmed independently, ideally by multiple observatories. The Wow! Signal, remarkable as it was, remained a single anomaly in the sky.
By the 1990s, as Ehman reflected on the signal with the benefit of time and additional data, his own assessment shifted toward natural or prosaic explanation—not because the signal had been fully explained, but because the absence of any follow-up detection, and the accumulation of alternative hypotheses (including the accidental transmission from a spacecraft, or background radio sources previously unknown to the catalogue), made intelligent origin seem increasingly unlikely. Yet he remained transparent: the Wow! Signal could not be conclusively explained. It was anomalous. But anomaly is not the same as signal.
Connection to the Signal
The Wow! Signal is the single most tantalising candidate for an extraterrestrial transmission ever recorded. It possessed every quality that SETI theory predicts a genuine signal should have: narrowband emission, no known source, anomalous strength, and appearance at a frequency associated with communication. In a parallel universe, it might have been the moment humanity recognised it was not alone. Instead, it became a permanent unanswered question—not because the observation was poor, but because the scientific method demands something more than a single remarkable event. It demands reproducibility.
Ehman's response to the Wow! Signal is nearly as important as the signal itself. He modeled how science should respond to an anomalous claim: with excitement tempered by scepticism, with publication and transparency, with calls for independent verification, and with honest acknowledgment of uncertainty. He resisted the pressure to become either a true believer or a dismisser. He remained, in the best tradition of science, uncertain—but confident in the method that would resolve the uncertainty if resolution were possible.
This approach has become the gold standard in SETI research. When Andrew Siemion's team at Berkeley investigated the BLC1 signal candidate from Proxima Centauri in 2020, they followed the Ehman template: rigorous analysis, open publication, and honest assessment of limitations. The Wow! Signal taught SETI researchers that the most important detection would be one that demanded explanation—and the most scientific response would be to explain it rigorously, even if the explanation undermined the exciting hypothesis.
Legacy
Jerry Ehman passed away in 2015, having never seen the Wow! Signal explained. Yet his legacy in SETI research endures as perhaps the most important: the insistence that credibility depends on method, not outcome. He showed that a scientist could spend decades engaged with a mystery—genuinely curious, genuinely open to the possibility of discovery—without abandoning the standards that separate science from speculation.
The Wow! Signal remains in the historical record as the most anomalous narrowband radio signal ever detected. But it is also, permanently, Jerry Ehman's signal—not because he invented it or explained it, but because his careful, honest, generous response to the mystery became the model for how SETI research should be conducted. In that sense, his greatest discovery was not the signal itself, but a method.
On This Site
Jerry Ehman's role in SETI history is central to our exploration of how science responds to cosmic mysteries. Read the full story of the Wow! Signal in The Wow! Signal, and explore why, nearly five decades later, it remains Still Unknown After 45 Years. His cautious, rigorous approach defines how modern SETI researchers investigate candidate signals.