The Claim
On August 15, 1977, astronomer Jerry Ehman, working with Ohio State University's Big Ear radio telescope on a search for extraterrestrial intelligence, detected an unusually strong, narrowband radio signal lasting 72 seconds, apparently coming from the direction of the constellation Sagittarius. Startled by its strength, he famously circled the data printout and wrote “Wow!” in the margin.
The Evidence
- The signal's genuine, unusually strong intensity, far exceeding typical background noise.
- Its narrow radio frequency, close to the theoretical “water hole” band some scientists proposed alien civilizations might use to communicate.
- The signal's total non-repetition despite extensive, repeated follow-up searches of the same location.
The Official Story
The Wow! Signal has never been detected again despite decades of dedicated follow-up observation, and no fully satisfying conventional explanation has been confirmed, though proposed candidates include a passing comet's hydrogen cloud (a 2017 study) or a rare terrestrial radio interference event. It remains officially, genuinely unexplained — not confirmed alien contact, but not conclusively dismissed either.
File Notes
In 2012, on the signal's 35th anniversary, Arecibo Observatory transmitted a reply of over 10,000 tweets toward the same patch of sky — which, given the roughly 1,800-light-year distance, we should not expect a response to for quite some time.