April 24, 2024

The Wow Signal

In 1977 astronomers detected the Wow Signal, a short powerful burst of radio waves from deep space. Its origin is still unexplained.

Hubble Deep Field View
5 500 galaxies visible in Hubble’s ‘Deep Field’ view, covering a patch of sky about half the diameter of the moon.

Space, as Douglas Adams observed, is really big. In fact, its infinite: a boundary-less, still expanding, expanse.

Among the endless stretch of space, a finite, though still very large, number of stars. In 2021, NASA estimated there are about 200 billion galaxies, containing 10 to the power of 22 (1 followed by 23 zeros) worth of stars. And many of these, accompanied by orbiting planets.

The numbers are staggering.

Frank Drake
Frank Drake

With so many world’s available, many scientists think that life elsewhere is close to inevitable. Some effort has even been made to calculate the probability.

In 1961, American astronomer Frank Drake formulated the ‘Drake Equation’, an attempt to give a mathematical structure to this question.

To arrive at an estimate of the number of civilisations in our galaxy, Drake combined estimates of contributing factors; the number of stars, planets, habitable planets, habitable planets where life may arise, and so on. An escalating order of difficulty to provide an overall estimate of the occurrence of intelligent life.

The Drake equation
The Drake equation, where ‘N’ equals the number of other civilisations in our galaxy.

Drake’s original calculation arrived at an answer of 20 other galactic civilisations.

In the ensuing decades, other scientists have applied their own figures, and come up with a range of answers, everything from 1 (meaning we are alone in the universe), to many millions.

But if there is a chance that other intelligent life is out there, somewhere, another question arises. One that was most famously summarised by Italian physicist Enrico Fermi, when discussing the question with his colleagues:

‘Where is everybody?’

These conflicting ideas, the likelihood of other civilisations, and our lack of contact with them, is now known as the ‘Fermi Paradox’. To try and answer this question, scientists have attempted to detect possible communications from beyond the Earth.

Our primary method involves radio astronomy.

Karl Janskey and his radio receiver
Karl Janskey and his radio receiver

Radio astronomy was discovered by accident.

In 1932, Karl Guthe Jansky was an engineer working for Bell Telephone Laboratories, in New Jersey. Janskey was looking to reduce interference with radio and telephone communications, analysing short wave transmissions with a basic receiver.

Janksey’s antenna was 30 metres long and 6 metres high, and operated by hand. He would manually rotate the antenna, then sit in an adjacent shed, listening to the signals it picked up and and writing down his observations.

The main cause of radio interference he detected were thunderstorms, whose electric charge produced natural radio emissions.

But Janskey also detected something else: a faint, constant, static hiss. This interference seemed to come from everywhere, right across the sky, and he struggled to find an explanation.

Through careful observation, Janskey eventually determined that his hiss conformed to a pattern, that reset every 23 hours and 56 minutes. This perfectly matched the rotation of the earth, and suggested these radio signals were coming from deep space.

This accidental discovery caused a revolution in astronomy. World War II led to great advances in radio technology, and after the war this was deployed in the first, large scale, purpose-built radio telescopes.

The electromagnetic spectrum

Radio telescopes are slightly misnamed, in that radio waves are only one thing that they search for.

They are really electromagnetic radiation detectors, which span a spectrum of signals from intense gamma rays, through x-rays and visible light, through to low intensity radio waves.

Radio astronomy has vastly improved our understanding of the universe, being able to observe objects much further away, and fainter, than optical telescopes.

Cocconi and Morrison's famous paper in 'Nature'
Cocconi and Morrison’s famous paper in ‘Nature’

In 1959, Giuseppe Cocconi and Phillip Morrison, psychists at Cornell University, proposed a novel use for radio astronomy. They published a paper in the journal ‘Nature’, speculating on possible communications by an alien civilisation, and suggesting radio waves as the likeliest medium.

Radio waves do not require much power to generate, and can travel vast distances while retaining signal integrity. They are also relatively simple science, meaning an intelligent species should understand how to generate and detect them.

Hydrogen is the most common substance in the universe, and produces electromagnetic radiation at a frequency of 1420 Mhz. Cocconi and Morrison suggested aliens may use this frequency, as a kind of interplanetary calling card: the properties of hydrogen should also be understood by any advanced species.

Finally, they suggested the signal would likely be ‘narrow band’. This meant it would be concentrated at 1420 Mhz, rather than a range of frequencies, as this would conserve power. Narrow band transmissions have another advantage, as they rarely occur naturally.

Cocconi and Morrison’s ideas were hypothetical, but logical, and widely discussed.

The Big Ear telescope
The Big Ear telescope

In 1963, Ohio State University built its own radio telescope, dubbed the ‘Big Ear’.

The Big Ear had an unprepossessing design: it looked a bit like a half finished football stadium. Constructed in an open space, it featured two metal receivers, separated by a flat, 103 metre wide reflector.

The telescope could not move greatly, but would rather rely on the rotation of the earth, to allow it to examine different parts of the sky.

The speed of our planet’s rotation meant each receiver would view what it was observing for 72 seconds, before that spot rotated out of range. And the gap between the two receivers meant each one would look at the same spot, separated by a time lag of 3 minutes.

Big Ear was used by students and scientists, for a range of astronomical observations. Among these, in 1973 it began scanning the skies for signals of extra-terrestrial origin.

The suggested frequency of 1420 Mhz was included in the search parameters.

A receiver at the Big Ear observatory
A receiver at the Big Ear observatory

Big Ear surveyed the sky automatically, slowly accumulating data throughout the night.

The signals it detected were stored on a primitive hard drive, with a capacity of 1 megabyte. Every few days, a technician would print out the accumulated observations for analysis, wipe the hard drive, and reset the system.

The printouts showed a grid of letters and numbers, that reflected the intensity of any signals received. Each grid point represented an observation time of 12 seconds.

A blank space indicated nothing had been detected, a zero the lowest level of signal. The numbers would then climb, from 1 to 9, as the signal strength increased. If the signal grew even more powerful, the system would switch to letters, from A to Z.

Mostly, Big Ear detected nothing. Sometimes, the faint background noise of space, as originally observed by Karl Janskey.

Occasionally, it picked up a more powerful signal, but these had then been determined to be specific astronomical objects, or a terrestrial signal, of Earth origin.

The Wow Signal
The Wow Signal

On August 15, 1977, at 11.16pm, a powerful radio signal hit the first Big Ear receiver.

The system recorded its arrival, increasing strength, and then departure, as the rotation of the earth moved it out of range. When the second receiver scanned the same spot three minutes later, the signal was gone.

It would be several days before anyone knew what had happened. Jerry Ehman, a scientist attached to the project, was the first to see the signal’s detection:

‘Ehman was in his kitchen when he read the printout from Big Ear. He was sitting at the table, with three days data in front of him.


The signal came in as 6EQUJ5, the signature of a signal that steadily grows in intensity, reaches a peak, then falls away again. The U was the highest power signal the telescope had ever seen.


Ehman knew what Cocconi and Morrison had said about the likely shape of alien signals. This fit exactly. By anyone’s definition it was a narrowband signal at 1420 Mhz.’


– Michael Brooks, ’13 Things That Don’t Make Sense’

In his excitement at what he was looking at, Ehman circled the signal on the printout and wrote the note alongside it that would give it its name: Wow!

The Wow signal origin in the night sky
The Wow signal origin in the night sky

But as soon as the Wow signal had been detected, it revealed additional layers of mystery. For starters: Big Ear could not find it again.

Right from the first analysis, Ehman and his colleagues thought it strange that the second receiver had not also detected the signal. There had been a brief, intense radio signal from the sky, that the same equipment could not relocate, 3 minutes later.

Big Ear would return to examine the same location in the following days, and then hundreds more times over the following years. Other radio telescopes would try the same thing. The signal has never been detected again.

The Wow signal origin on a star map: empty space
The Wow signal origin on a star map

And so the scientists turned into detectives, trying to determine what the data they did have was telling them. It was a process of elimination, as they crossed off potential sources.

For starters, they looked to see if an existing astronomical object occupied that place in the sky.

The Wow signal originated in the constellation of Sagittarius, part of a formation also known as ‘The Teapot’. Astronomical charts and observations from other telescopes indicated this was empty space.

No known object was found in this location.

They then scrutinised records of satellites and objects in earth’s orbit, to see if one of these could provide an explanation. Terrestrial aircraft were examined as well.

There was also no record of any craft within range of the observatory, at the time the signal was received.

Jerry Ehman
Jerry Ehman

Ehman and his colleagues wondered if it could be an earth based signal, bouncing off the atmosphere, or even off debris, and so appearing to originate in space. They analysed satellite transmissions, radio transmissions, TV broadcasts, aircraft communications, and other defense signals; none of them matched the data.

This solution has an additional problem: the bandwidth of 1420 Mhz, where the Wow signal was received, is prohibited from use by global agreement. No official transmissions use this frequency.

Over the ensuing years, then decades, scientists continued to review the data. But for lack of new information, the case eventually went cold.

The university eventually sold the land Big Ear stood on. The telescope was demolished in 1998.

The Wow signal solved: 2017
The Wow signal solved: 2017

In 2017, news headlines dramatically announced that the mystery had been ‘solved’.

Professor Antonio Paris, of St Petersburg College, had detected a pair of previously unknown comets, that would have crossed Big Ear’s path in 1977. Professor Paris claimed these as the signal’s origin.

But despite the initial excitement, this explanation was quickly debunked. While the comets were real enough, they do not produce signals of the type detected by Big Ear. Once scientists examined the claim in detail, it was noted that no other comets had been observed to, either.

The Wow signal remains, officially, unsatisfyingly, unexplained. There is likely a non-alien explanation, many long-standing mysteries in science are eventually solved, but what this is remains elusive.

Jerry Ehman keeps an open mind. He has told journalists that he doesn’t believe the Wow signal is proof of extra terrestrial intelligence, but he is still waiting for that better explanation.

The globular star cluster M13
The globular star cluster M13

One unusual aspect of the Wow signal is its brevity, and non-repetitive nature.

If it was an alien civilisation signalling, why would they beam a transmission only once, for less than three minutes? This surely makes no sense.

Except: we have done this same thing ourselves.

In 1974, scientists at the Arecibo radio telescope in Puerto Rico broadcast a powerful radio message, directed at the globular star cluster M13. M13 is about 25 000 light years distant, and thought to be a good candidate location for extra-terrestrial life.

The message was the brainchild of Frank Drake, of Drake’s equation, and was worked on by famed astronomer Carl Sagan. In binary code, it delivered information outlining atomic numbers of common elements, basic chemistry formula, and graphics of our DNA, the Solar System, and the telescope that sent it.

It was a playful exercise, sending a message out into the universe, announcing our presence, without ever hoping for a response.

The duration of the signal? It was broadcast once, for less than 3 minutes.


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