6EQUJ5: The WOW! Signal - Unraveling the Mystery Behind Space's Most Intriguing Message

Six characters on a computer printout — 6EQUJ5 — have kept astronomers arguing for nearly fifty years. On 15 August 1977 a radio telescope in Ohio recorded a 72-second burst at the one frequency the universe’s hydrogen sings on, strong enough that the astronomer who found it wrote “Wow!” in the margin. It has never repeated. In August 2025 a new analysis of the original tapes found it was four times stronger than anyone thought, and offered the most serious natural explanation yet. Here is the full story, updated.

The printout

6EQUJ5

Each character is one 12-second reading of signal strength: 0–9, then A–Z. “U” = 30 times the background noise — the highest value Big Ear ever recorded.

The five numbers that define the mystery

72 secondsExactly how long a fixed point in the sky stays in Big Ear’s beam as Earth rotates — the signal rose and fell precisely as a real cosmic source should.

1420 MHzThe hydrogen line — the frequency astronomers had predicted an alien civilisation would use, and one Earth transmitters are banned from.

0 repeatsIn over 100 follow-up searches with far bigger telescopes, including the Very Large Array, it has never been seen again.

>250 JyIts peak strength per the 2025 reanalysis — four times the figure quoted for 48 years.

3 daysBefore anyone saw it. Jerry Ehman found it on 18 August, reviewing the printout at his kitchen table.

12 facts about the Wow! signal

The night it arrived

1. Nobody was watching. Big Ear ran unattended, printing numbers; volunteer astronomer Jerry Ehman spotted the sequence three days later and circled it in red pen with the word “Wow!”.
2. Big Ear wasn’t a dish. Ohio State’s telescope was a flat reflector the size of three football fields that couldn’t steer; it waited for the sky to drift past. That is why every source gets a 72-second window.
3. The signal was heard by only one of two “ears”. Big Ear had two feed horns a few minutes apart; the signal appeared in one and not the other. Either it switched off in between — or it was only ever in one beam, which is one of the real puzzles.
4. It came from Sagittarius, near the star group Chi Sagittarii, toward the centre of the Milky Way — and because of the two-horn ambiguity there are two possible sky positions, not one.
5. It was narrowband. Natural radio sources usually spread across many frequencies; the Wow! signal was confined to a sliver under 10 kHz wide — exactly what an artificial transmitter would produce, and what makes it hard to dismiss.

The hunt for an explanation

6. Earth is ruled out, mostly. 1420 MHz is a protected band with no legal transmitters; no satellite or aircraft matched the time and position; and reflected signals don’t fit the clean 72-second shape.
7. The comet theory failed. In 2017 Antonio Paris proposed two comets passing through the region. Astronomers pointed out neither comet was in the beam that day and comets are far too faint at that frequency; the idea is not accepted.
8. A Sun-like star was proposed as a source. In 2022 amateur astronomer Alberto Caballero identified 2MASS 19281982-2640123, 1,800 light-years away, as the only Sun-like star in the candidate zone — a target, not an answer.
9. The 2025 reanalysis changed the numbers. 2025 Abel Méndez’s “Arecibo Wow!” team re-processed the original Ohio State data and found the peak was over 250 Jy, four times the textbook value, at 1420.726 MHz — implying a source moving faster than assumed.
10. The leading natural idea: a hydrogen cloud lit up by a magnetar. Méndez proposes a “superradiance” flash — a cold hydrogen cloud briefly amplified by a burst from a dying star’s flare. Rare, never observed before, and still a hypothesis: “This study doesn’t close the case,” he says.
11. Humanity replied anyway. On the 35th anniversary in 2012, Arecibo beamed 10,000 Twitter messages and videos toward the Wow! coordinates. If anyone is there, the reply would take at least 3,600 years.
12. The telescope is now a golf course. Big Ear was torn down in 1998 to expand a housing development and golf course. The printout survives in the Ohio History Connection archive.

Wow! signal audio

There is no recording of the signal itself — Big Ear only logged numbers. This is a reconstruction of what a 72-second narrowband tone rising and falling through the beam would sound like.

Explanations, ranked

Hypothesis	Status	Problem
Earth interference	Unlikely	Protected band; clean transit shape
Comets (2017)	Rejected	Wrong place, far too faint
Hydrogen cloud + magnetar flash (2025)	Leading natural candidate	Never seen before; unconfirmed
Extraterrestrial transmitter	Not ruled out	Never repeated; no second detection

Myth busters

Three Wow! signal “facts” the internet keeps getting wrong

✗“6EQUJ5” is a coded message from aliens.
It is the signal’s loudness over 72 seconds, one character per 12 seconds. The letters are a strength scale, not words.

✗The signal was recorded and you can listen to it.
Only intensity numbers were logged. Every “Wow! signal audio” online is a reconstruction.

✗Scientists have finally solved it.
The 2025 magnetar-hydrogen idea is the best natural explanation so far, but its own authors call it unproven. The case is open.

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Sources: EarthSky – the 2025 Wow! signal reanalysis · Centauri Dreams – Arecibo Wow! findings · Arecibo Wow! project – Planetary Habitability Laboratory · Big Ear Radio Observatory – Jerry Ehman’s own account · Wow! signal – overview and follow-up searches

Last fact-checked: October 2026.