In August 1977 Ohio State University’s Big Ear radio telescope was scanning the sky as part of a search for signals from other civilisations. Its computer printed the strength of radio noise in each channel as a column of numbers and letters. A few days later the volunteer astronomer Jerry Ehman was reading through the printouts from the night of 15 August when he saw a sequence that stood out: 6EQUJ5. He circled it and wrote “Wow!” in the margin. The name stuck.
What 6EQUJ5 means
It is not a message. Each character is the signal strength in one 12-second interval, with numbers for low values and letters for higher ones. The sequence rose and fell over 72 seconds, peaking at “U”, about 30 times stronger than the background noise. Big Ear was fixed in place and scanned the sky by letting the Earth turn, so any point in the sky stayed in its beam for exactly 72 seconds. The signal’s rise and fall matched that perfectly: it behaved just as a source fixed among the stars should.
It was also very narrow, less than 10 kHz wide, and close to 1420 MHz, the frequency at which hydrogen naturally emits. That frequency had been suggested as an obvious channel for anyone trying to be heard across interstellar space. Natural sources of radio waves usually spread across a much wider range of frequencies.
Never heard again
The signal came from the direction of Sagittarius. Astronomers have pointed telescopes there many times since, including the Very Large Array in the 1990s and Breakthrough Listen in 2022. Nothing like it has been found. A one-off signal cannot be confirmed, and without a repeat it cannot be studied.
Explanations
In 2017 Antonio Paris proposed that hydrogen around a passing comet caused it; other astronomers, including members of the original team, rejected the idea. In 2020 Alberto Caballero identified a Sun-like star in the area as a possible source, but no signal has been found from it. In 2024 Abel Méndez and colleagues suggested a natural explanation: a sudden flare from a magnetar briefly brightened a cold cloud of hydrogen, making it shine like a radio laser. That idea has not yet been confirmed.
Big Ear itself no longer exists. It was demolished in 1998 to make way for a housing development and golf course. The Wow! signal remains the most famous unexplained radio signal ever recorded.