The Wow! signal: what 6EQUJ5 means, and is the mystery solved?

The Wow! signal was a strong burst of radio waves that the Big Ear radio telescope in Ohio recorded for about 72 seconds on 15 August 1977. The astronomer Jerry Ehman spotted it on a computer printout a few days later, circled the characters "6EQUJ5" and wrote "Wow!" next to them. It came from the direction of the constellation Sagittarius, at a frequency very close to the natural radio "note" of hydrogen. Nobody has detected it again, and its origin is still unknown. The quick facts:

What was the Wow! signal?

A radio telescope measures how much radio energy arrives from a patch of sky. For this observation, Big Ear recorded signal strengths rather than an image. In 1977 it was part of the Ohio State University's search for signals from other civilisations, a kind of search called SETI (the Search for Extra-Terrestrial Intelligence). The telescope did not move. As Earth turned, the sky slowly drifted past it, and a computer printed the signal strength in 50 narrow radio channels, row after row.

In his report, Ehman says the signal "entered the receiver of the Big Ear radio telescope at about 11:16 p.m. Eastern Daylight Savings Time on August 15, 1977." He found it "a few days after" (probably on 19 August) during a routine check of the printout. He marked the six characters in red pen and wrote "Wow!" in the margin, which gave the signal its name. You can see a scan of the original printout in Ehman's report.

Two things made it stand out. It was very strong, and it was narrowband: almost all of its energy fitted into a single 10 kHz channel. Ehman writes that narrowband sources "are almost always purposely generated by intelligent beings", such as radio and TV broadcasts, satellites and radar. That is why SETI researchers look for exactly this kind of signal. But "made by someone" is not the only possible answer, as you will see below.

Big Ear itself no longer exists. According to Ehman's report, it was "destroyed in 1998 by land developers" to enlarge a golf course.

What does 6EQUJ5 mean?

6EQUJ5 is not a decoded message. It is six measurements of the same radio channel, taken one after another. Each character is the signal strength during a 10-second sample, written as a multiple of the background noise. To fit big numbers into one character, the printout used the digits 1 to 9 and then letters: A = 10, B = 11, and so on up to Z = 35. Values below 1 were left blank. The values were rounded down, so "U" means at least 30 but less than 31.

Ehman's report gives the strongest reading, U, as "30.5 +/- 0.5 times stronger than the background noise". A new row was printed about every 12 seconds, so six readings cover about 72 seconds.

The numbers rise and fall in a smooth hump. That is the pattern you expect when a fixed point in the sky drifts through the telescope's beam (the patch of sky the telescope is sensitive to): weak at the edge, strongest in the middle, weak again. We fitted an approximate bell curve to the middle of each range (our calculation, not an exact reconstruction). It peaks at about 30 times the noise and is about 39 seconds wide at half its height.

If you searched for the "Wow! signal sound" or audio: the original data are numbers on a printout, not a sound recording. The only sound Ehman's report mentions is the printer's "ka-chunk". Audio online should not be mistaken for an original recording; it may be a reconstruction or an illustration.

Why was it recorded for 72 seconds, and only once?

Big Ear had two feed horns side by side at the focus of its reflector, so it had two beams that each looked at a slightly different spot in the sky. As the sky drifted past, a source in space should have passed through one beam and, a few minutes later, through the other. In Ehman's words: "we should have seen it twice within a period of about 5 minutes as our two beams sequentially scanned the position of the source, but we only saw one of the beam responses."

From the two sky positions in his report, the gap between the beams works out to about 2 minutes 51 seconds (our calculation). Nobody knows which beam caught the signal, so the missing crossing could have come about three minutes before or after it. That is why there are always two possible positions. The animation shows one of the two possible orders, with the sky moving 15 times faster than in reality.

The 72 seconds is how long a fixed spot in the sky took to drift through one beam. It is the length of the recording, not a measured start and stop: we do not know how long the source itself was sending. A steady source would have shown up in both beams, so the source probably changed in strength between the two crossings, getting brighter or fainter.

Was it seen again? Ehman recalled that Big Ear stayed on the same strip of sky "for the next 60 days or so and didn't see the Wow! signal again". The 2025 re-analysis of the archived Ohio data describes it differently: "Only three scans were performed at the declination of the Wow! Signal, but only the final scan, conducted 48 hours later, covered again its right ascension." In other words, the logs show only one later pass over the same spot. Either way, the signal was not seen again, and later searches with other telescopes found "no repeat detections" (Arecibo Wow! I).

Why 1420 MHz? The hydrogen line

Hydrogen is the most common element in the universe. Cold hydrogen gas in space gives off radio waves at one very precise frequency: 1420.4056 MHz (megahertz, millions of waves per second), which corresponds to a wavelength of about 21 centimetres. Astronomers call it the hydrogen line, and the radio band around it is protected so that telescopes can hear it.

That protection answers a common question: why is 1420 MHz "forbidden"? The international radio rules, reproduced in the US Code of Federal Regulations, say: "All emissions are prohibited in the bands 1400-1427 MHz". Ehman concluded that "no transmitter on earth or in space should have been transmitting in the protected band around 1420 MHz." A ban is not a guarantee, though: the 2025 study notes that it "does not completely rule out the possibility of illegal or unintentional interference".

SETI researchers listened near the hydrogen line on purpose. Ehman's reasoning was that a civilisation "desirous of attracting attention to itself might broadcast a strong narrowband beacon signal at or near the frequency of the neutral hydrogen line", because every radio astronomer knows that frequency.

The Wow! signal was not exactly on the line, and there are two estimates of its frequency from the same 1977 data. Ehman gave 1420.4556 ± 0.005 MHz, about 50 kHz above the line. In 2025, Abel Méndez and colleagues re-analysed the old Ohio data and found 1420.726 ± 0.005 MHz, about 320 kHz above it. Ehman's value already included a correction for one receiver setting. The 2025 team found that the receiver's channels ran in the opposite order to what had been assumed, and they used a corrected value for a second internal setting (the "2nd local oscillator"). If the signal came from hydrogen gas, a shift like this could mean the gas was moving toward us; the authors write that it implies "a galactic source with a substantially higher radial velocity than previously assumed" (radial velocity means speed toward or away from us). That does not identify the source.

Where in the sky did the Wow! signal come from?

Ehman's report puts the source "in the direction of the constellation Sagittarius", the Archer. Astronomers give sky positions as coordinates called right ascension and declination, sky addresses similar to longitude and latitude on Earth. The 2025 re-analysis narrowed the position to two neighbouring fields, centred on right ascension 19h25m02s or 19h27m55s (± 3 seconds) and declination −26°57′ (± 20′). These are J2000 coordinates, the standard grid of sky addresses referenced to the year 2000; when entering them, select J2000 if the app offers that setting. Each field is much longer from north to south than it is wide, because the beam was tall and narrow. We checked with the Astronomy Engine library that both fields lie in Sagittarius.

No particular star, planet or gas cloud has been identified as the source, and its distance is unknown. The fields lie about 4 degrees east of the handle of the "Teapot", the shape made by the brightest stars of Sagittarius (our calculation). From Big Ear in Ohio, this part of the sky never rises more than about 23 degrees above the southern horizon (our calculation).

You can find the spot yourself. From the northern United States, Sagittarius is low in the south on summer evenings: on 15 August 2026, the first field crossed due south from New York at about 10:45 p.m. EDT, about 22 degrees up (our calculation). Our Stellarium Web guide shows how to search for coordinates like these in a free planetarium app.

Has the Wow! signal been solved?

No. As of October 2026, nobody has proven where the Wow! signal came from. Ehman himself wrote that "the origin of the Wow! signal is still an open question for me. There is simply too little data to draw many conclusions." He chose, as he put it, not to "draw vast conclusions from 'half-vast' data".

Here is where the main explanations stand:

The newest idea comes from the Arecibo Wow! project led by Abel Méndez at the University of Puerto Rico at Arecibo. Using the Arecibo telescope in 2020, the team found weaker narrowband signals near the hydrogen line, which they say "are easily identifiable as small interstellar clouds of cold hydrogen (HI) in the galaxy." They suggest the Wow! signal was "a sudden brightening of the hydrogen line in these clouds triggered by a strong transient radiation source, such as a magnetar flare or a soft gamma repeater". A magnetar is a dead star with an extremely strong magnetic field that can flare violently. Their 2025 re-analysis adds "support for the hypothesis that the Wow! Signal most likely had an astrophysical origin rather than being attributed to radio interference."

So has it been debunked? No. Both studies are preprints, research papers shared before confirmed publication in a journal; when we checked their arXiv records on 20 October 2026, neither listed a journal reference. The authors themselves say that identifying the trigger "would prove challenging". The alien explanation has not been disproven either, but one short signal that never repeated is far from proof. For the bigger picture, see our article on whether there is life on other planets.

Wow! signal FAQ

Has the Wow! signal been solved? No. A 2024 study suggests a natural flare in a cold hydrogen cloud, but this has not been confirmed, and Ehman called the origin "still an open question".

What did the Wow! signal mean? No message was decoded. The six characters record signal strength, and these averaged measurements cannot show whether the radio signal carried information. Its importance lies in what it could be: an unusually strong, narrowband signal near the hydrogen line, the kind SETI searches were built to find.

What does 6EQUJ5 mean? Six readings of signal strength, as multiples of the background noise: 6, then E = 14, Q = 26, U = 30, J = 19 and 5. Each value was rounded down, so U means at least 30 but less than 31.

Why is 1420 MHz forbidden? Because the hydrogen line, at 1420.4056 MHz, is used by radio astronomers. International rules prohibit all emissions between 1400 and 1427 MHz to keep that band quiet.

Where was the Wow! signal picked up? By the Big Ear radio telescope of the Ohio State University Radio Observatory in Delaware, Ohio. The signal came from the direction of Sagittarius.

Did Earth receive a signal from space in 1977? Big Ear recorded an unexplained signal on 15 August 1977 whose rise and fall fitted a distant source drifting through the beam with the sky. Ehman found no Solar System planets or known satellites in the beam and argued against aircraft, but its origin remains unconfirmed.

Has the Wow! signal been debunked? No. A 2015 comet explanation was rejected by Ehman and by the Ohio State SETI program, and the newer hydrogen-cloud idea is still a hypothesis in preprints.

Is there a recording of the Wow! signal? Only as numbers on the original computer printout. Audio online is not an original recording; it may be a reconstruction or an illustration.

Can aliens detect our radio waves? Possibly. It depends on distance, on how sensitive their receivers are and on whether our signals point their way. A 2025 study led by Sofia Sheikh (SETI Institute) found that planetary radar, such as the radar of the former Arecibo Observatory, is Earth's most detectable sign of technology, "potentially visible from up to 12,000 light-years away" with equipment like ours. Preliminary work presented at a Royal Astronomical Society meeting in 2025 found that airport radar leaking into space could be picked up "as far as 200 light-years away" by a telescope like the Green Bank Telescope. These are distances at which detection would be possible, not distances our radio signals have already travelled.

How we checked

Our main source is Jerry Ehman's own report on the Wow! signal on the Big Ear website (original draft 2007, last revised 2010), plus the Arecibo Wow! I (2024) and II (2025) preprints, the US Code of Federal Regulations for the protected band, and the Planetary Habitability Laboratory page on the comet claim (Méndez's own lab). The full list is under Sources. We checked all sources on 20 October 2026.

The decoded values, the bell-curve fit, the time between the beams, the constellation check and the sky positions are our calculations from those numbers (Astronomy Engine; the sky view was simulated in Stellarium). The animation uses idealised beam shapes. None of the images or videos is AI-generated.