Strangest fact
In 1977 a radio telescope picked up a 72-second signal about 30 times stronger than the background. An astronomer circled it and wrote 'Wow!'. It never came back.
Why it is odd: It looked just like a signal from a fixed point in space, yet no telescope has ever caught it again.
In 1977 Ohio State University ran a radio telescope called Big Ear, which searched the sky for signals that might come from other civilizations. That search is called SETI, the Search for Extraterrestrial Intelligence. The telescope stayed still and let the Earth's turning sweep the sky past it, and a computer printed the results as columns of numbers and letters.
Astronomer Jerry Ehman wrote that the signal entered the receiver at about 11:16 p.m. Eastern Daylight Time on August 15, 1977. Days later, reading the printout, he saw the sequence 6EQUJ5 in one column, circled it in red and wrote "Wow!" beside it. Each character shows how strong the signal was in a 12-second window. Ordinary background noise showed as blanks and low numbers; the letter U meant the signal was about 30 times stronger than the noise.
Several things made it exciting. The signal was very narrow, sitting on a single channel close to 1420 megahertz, the natural radio frequency of hydrogen, which SETI researchers had long suggested other civilizations might use. And it rose and fell over 72 seconds (six readings, 12 seconds apart), which is the pattern a source fixed in the sky would make as Big Ear swept past it.
There was a puzzle too. Big Ear had two horns, two receivers that looked at the sky one after the other, so a fixed source should have shown up twice, a few minutes apart. It appeared only once. Ehman's team watched the same strip of sky for about 60 days afterward and saw nothing, and later searches by other telescopes also failed. Ehman wrote in 2007 that the origin of the signal was still an open question for him.
In 2024 a team led by astrobiologist Abel Mendez of the University of Puerto Rico at Arecibo proposed a natural cause. Searching old Arecibo Observatory data from 2020, they found fainter signals of the same kind coming from cold clouds of hydrogen gas. They suggested that a sudden burst of energy, perhaps from a magnetar, a kind of dead star with a huge magnetic field, made one such cloud briefly glow very brightly at the hydrogen frequency, like a natural laser. Other astronomers called the idea interesting but noted that such events would have to be rare.