Wow signal explained: was the 1977 radio signal from aliens?

What happened on 15 August 1977

Big Ear was a radio telescope run by Ohio State University, built in 1963, and by 1977 it was being used to search for signals from other civilisations. It did not steer. It pointed at a fixed strip of sky and let the Earth's rotation carry the stars through its beam. On the night of 15 August 1977, at about 11:16 p.m. Eastern Daylight Time, a strong signal passed through. Nobody was watching. The telescope's computer wrote it to a printout, and the astronomer Jerry Ehman, going through the sheets a few days later, circled the entry in red ink and wrote "Wow!" beside it.

The entry reads 6EQUJ5. Each character is a signal-to-noise reading taken about every 12 seconds, with digits standing for their own value and letters for 10 to 35. Read in order they give roughly 6, 14, 26, 30, 19 and 5: a signal that rose, peaked at about 30 times the background noise, and fell, which is the shape a fixed point in the sky makes as it drifts through the beam. It appeared in only one of the receiver's 50 channels, at 1420.4556 MHz, very close to the frequency at which neutral hydrogen radiates. That frequency had long been suggested as the one an alien transmitter might choose, because hydrogen is the commonest element.

Why it lasted 72 seconds and why there is no footage

The 72 seconds are a property of the telescope, not the source. Big Ear's beam took about that long to sweep across a single point, and the six readings cover six 12-second intervals. Ehman notes in his 20th-anniversary report that the signal could not have lasted much more than two and a half minutes, because Big Ear had two feed horns scanning side by side, and a source that stayed on would have appeared in the second horn's pass as well. It did not. Which of the two horns caught it was never recorded, so even the right ascension is ambiguous: about 19h25m or 19h28m (epoch 2000), at a declination of −26°57′, in Sagittarius.

People searching for Wow signal footage will not find any. There was no video, no audio and no live operator; the only record is the printout. Big Ear itself was dismantled in 1998.

The follow-ups that failed

The telescope stayed on the same strip of sky for at least a month after the detection and saw nothing; Ehman gives the period as about 30 days in his 20th-anniversary report and about 60 in his 30th. The same strip of sky was scanned many times in later years, again with nothing. Other observatories have looked since, and the signal has never repeated. Ehman worked through the ordinary explanations in his 1997 and 2010 reports: planets, asteroids, satellites, aircraft and spacecraft were ruled out or judged very unlikely, and a ground transmitter bouncing off a piece of space debris he gave a low probability. His own summary has not changed in decades: "the origin of the Wow! signal is still an open question for me."

The comet explanation and its rebuttal

In 2017 Antonio Paris, an astronomer at St. Petersburg College in Florida, proposed in the Journal of the Washington Academy of Sciences that the signal came from comet 266P/Christensen, which was not discovered until 2006 and so would have been unknown in 1977. He had earlier suggested a second comet, P/2008 Y2 (Gibbs).

The people who ran Big Ear rejected it. Ehman and Robert Dixon, director of the Ohio State radio observatory, pointed out that a comet moves slowly enough that both feed horns should have recorded it about three minutes apart, and only one did. Seth Shostak of the SETI Institute said he knew of no comet that emitted at that frequency in the way required. Paris conceded that the feed-horn problem was unexplained.

The 2024 hydrogen-cloud hypothesis

The most serious recent attempt is a preprint posted to arXiv on 16 August 2024 by Abel Méndez, Kevin Ortiz Ceballos and Jorge Zuluaga, titled Arecibo Wow! I. Going through drift-scan data taken at Arecibo between February and May 2020 at 1420 MHz, they found narrow signals, about 10 kHz wide, near the hydrogen line, at several places in the sky, that look like the Wow! signal but about a hundred times weaker. They attribute those to small clouds of cold interstellar hydrogen. Their hypothesis is that in 1977 one such cloud was briefly lit up by a powerful transient behind it, a magnetar flare or soft gamma repeater, producing a maser-like burst in the hydrogen line. If so, the Wow! signal would be the first recorded event of its kind, and a new source of false positives for technosignature searches.

That is where it stands: a hypothesis in a preprint that its arXiv listing describes as submitted to The Astrophysical Journal, with the mechanism argued to be consistent with the data rather than demonstrated. Méndez told National Geographic in 2026 that such events would be rare, which would explain why the signal has not recurred, and that the team had found similar signals with two independent telescopes, while acknowledging some doubt remains. Seth Shostak, quoted in the same article, said that when a result cannot be replicated it is impossible to say what caused it. Astronomy magazine's summary in August 2026 is that astronomers still do not know.

Verdict

The Wow signal of 1977 was real, strong and narrow, and the detection itself has never been seriously challenged. Everything after that is open. The signal was never confirmed by a second horn, a second telescope or a second night. No terrestrial source has been identified, and no alien one has been shown. The comet explanation failed its own test. The hydrogen-cloud idea is the best natural candidate so far, and it is still an idea. So is the Wow signal solved? No. Real or Legend files it as unsolved.