The Wow! signal was a strong, narrowband radio transmission detected on August 15, 1977, by astronomer Jerry Ehman at Ohio State University's Big Ear radio telescope. Lasting 72 seconds, it matched the expected profile of an extraterrestrial signal so closely that Ehman circled it on the printout and wrote 'Wow!' in the margin — a name that stuck. Despite decades of follow-up observations, the signal has never been detected again and its origin remains unexplained.
What Was the Wow! Signal and How Was It Detected?
Big Ear was scanning the sky as part of SETI (Search for Extraterrestrial Intelligence) when it recorded an unusually powerful signal near the 1420 MHz hydrogen line — the frequency many scientists believe an advanced civilisation might use to broadcast, because hydrogen is the most abundant element in the universe. The signal, encoded in the telescope's alphanumeric intensity scale, read '6EQUJ5', with the letter 'U' representing a peak intensity roughly 30 times the background noise level. It appeared to originate from the direction of the constellation Sagittarius. The telescope's fixed-dish design meant it could only observe any given patch of sky for 72 seconds as the Earth rotated, which is exactly how long the signal lasted — consistent with a genuine point source in deep space.
Why Did the Wow! Signal Excite — and Frustrate — Scientists?
The signal was exciting because it ticked nearly every box on the SETI checklist: it was narrowband (artificial signals are narrow; natural ones are broad), it came from the right frequency, and its rise-and-fall intensity pattern perfectly matched a signal from a fixed point beyond our solar system. The frustration came immediately after. Ehman and colleagues pointed Big Ear back at the same coordinates dozens of times over the following weeks and years, and heard nothing. Other observatories worldwide also failed to detect a repeat. Without confirmation, the signal could not be formally classified as extraterrestrial. Some researchers noted the absence of detectable modulation — no encoded message — but others argued a carrier wave alone would be a profound discovery.
| Property | Detail |
|---|---|
| Date detected | August 15, 1977 |
| Telescope | Big Ear, Ohio State University |
| Duration | 72 seconds |
| Frequency | ~1420 MHz (hydrogen line) |
| Signal intensity | ~30× background noise |
| Origin direction | Constellation Sagittarius |
| Confirmed repeat | Never |
What Are the Leading Explanations for the Wow! Signal?
Several hypotheses compete to explain the signal. The extraterrestrial intelligence hypothesis remains on the table precisely because no natural explanation has been definitively proven. In 2017, astronomer Antonio Paris proposed the signal was caused by hydrogen clouds surrounding comets 266P/Christensen or 335P/Gibbs, which were near that region of sky at the time — but critics noted Big Ear should have seen similar signals from comets before, and the comet hypothesis has not gained consensus. Radio frequency interference from Earth was largely ruled out because the signal appeared in only one of the telescope's two feed horns, consistent with a deep-space source rather than local interference, which would have triggered both. As of 2025, no single explanation has achieved scientific consensus, leaving the Wow! signal as the most tantalising unresolved event in the history of SETI.
