In 1977 a radio telescope caught 72 seconds that still have no explanation.
In August 1977 an Ohio radio telescope searching for alien signals recorded a strong, narrow burst near the frequency of hydrogen, exactly as a signal from space should look. The volunteer who spotted it on the printout circled it and wrote 'Wow!' It has never been heard again.
In 1959 the physicists Philip Morrison and Giuseppe Cocconi suggested that any civilisation trying to be heard across space might use 1,420 megahertz, the natural radio frequency of hydrogen, the most common element in the universe. From 1973 Ohio State University's 'Big Ear' radio telescope was devoted to the search for extraterrestrial intelligence, in what became the longest-running programme of its kind.
Jerry Ehman, working as a volunteer, analysed the data by hand from computer printouts. Reviewing observations from 15 August 1977, he found a run of characters, 6EQUJ5, circled it and wrote 'Wow!' in the margin. It is often mistaken for a coded message, but it simply records the signal's strength rising and falling. At its peak, 'U', it was about 30 times the standard deviation of the background noise. It came from the direction of the constellation Sagittarius and sat very close to the hydrogen frequency.
Its shape was striking. Big Ear used Earth's rotation to sweep across the sky, so it could watch any point for only 72 seconds, and a genuine signal from a fixed point in space should rise and fall smoothly over exactly that time. The Wow! signal did precisely that. The telescope had two receiving horns, and the signal appeared in only one, so its exact position is uncertain.
Every attempt to find it again, including by Ehman, has failed, and scientists stress that a signal seen once cannot be confirmed. Ehman at one point suspected an Earth signal reflected off space debris, though he later softened that view. A 2017 idea that two comets caused it was rejected. A 2024 preprint proposed a rare natural event: a cold hydrogen cloud suddenly brightening when energised by a star. The mystery remains open.
Source: Wikipedia — Wow! signal · Text summarised from Wikipedia (CC BY-SA 4.0)
