The SETI “WOW” signal comes from a computer printout of radio signals detected at the Big Ear Radio Observatory at Ohio State University in 1977. The strength and pattern of the signal sequence impressed researcher Jerry Ehman so much that he circled the sequence and wrote “WOW” on the printout.
Radio telescopes probe space for signals from stars and measurement of background radiation from the Big Bang. Stellar radio signals have a distinct signature, so the Search for Extraterrestrial Intelligence (SETI) project looks for different patterns and signal sequences that would indicate transmission by some intelligent entity. The sequence Jerry Ehman found showed many characteristics suggesting it was not background noise. He searched for a repeat signal for several weeks but never found it again. Various explanations about its origin still don’t provide a solid answer, so the “WOW” signal remains a mystery.