Wow! Signal

Shortly after 11 p.m. local time on August 15, 1977, the Big Ear radio telescope of Ohio State University, near Delaware, Ohio, recorded a strong narrowband signal close to the 1,420-megahertz hydrogen line from the direction of the constellation Sagittarius. Big Ear had been converted in 1973 to a full-time survey for artificial narrowband signals, run by former observatory staff in their spare time, and printed its readings unattended. A few days later, probably on August 19, Jerry Ehman, a former Ohio State astronomer then volunteering on the project, found the characters "6EQUJ5" in one channel of the printout, circled them in red ink and wrote "Wow!" in the margin.

The six characters are not a message but a measure of intensity in successive samples, rising to roughly 30 times the background noise and falling again. Because the fixed telescope relied on Earth's rotation to sweep the sky, any point stayed in its beam for 72 seconds, and the signal's rise and fall matched that beam pattern closely, as a distant, steady source would. Big Ear had two feed horns that should have seen a fixed source about three minutes apart, but the signal appeared in only one, and the data cannot show which, leaving two possible positions. In a 30th-anniversary report Ehman put the frequency at 1420.4556 megahertz.

No one has heard it again. Ehman searched with Big Ear in the following months, Robert Gray tried in 1987 and 1989 at Oak Ridge Observatory and in 1995 and 1996 with the far more sensitive Very Large Array, Gray and Simon Ellingsen made six 14-hour observations in Tasmania in 1999, and Breakthrough Listen found no technosignature candidates in 2022. Ehman's own view shifted. In 1994 he said "we should have seen it again" and suggested an Earth signal reflected off space debris; in his later report he concluded that a terrestrial origin seemed improbable and that an extraterrestrial intelligence "might have sent the signal," while refusing to "draw vast conclusions from 'half-vast' data."

Natural explanations have come and gone. In 2016 and 2017 Antonio Paris of St. Petersburg College proposed hydrogen clouds around comets 266P/Christensen and P/2008 Y2 (Gibbs). Robert Dixon, director of the Ohio State SETI program, rejected the idea in June 2017, calculating that the comets were nearly an hour of right ascension away from the signal's position and noting that comets were not known to emit at that frequency. In 2024 Abel Méndez and colleagues at the University of Puerto Rico at Arecibo reported faint narrowband hydrogen-line signals from small cold interstellar clouds in 2020 Arecibo Observatory data and proposed that a transient such as a magnetar flare made one such cloud brighten suddenly. A 2025 reanalysis of archival Ohio data by the same group measured a higher peak flux density, above 250 janskys, revised the frequency to 1420.726 megahertz and narrowed the position, which they said supports an astrophysical origin. A June 2026 paper by Méndez, Dixon and Russell Childers noted that the Ohio archive holds more than 40,000 other transient narrowband events, most still unexamined.

The signal remains a fixture of SETI history and of UFO and disclosure media, where it is often discussed alongside reports of craft although it is a radio detection, not a sighting. Posts on X and Reddit in 2026 asked whether it was first contact or whether humanity should "reach back." Nearly five decades on, the Wow! signal remains a single 72-second detection whose source has never been confirmed.