How the 'Wow!' Signal Works

By: Dave Roos & Austin Henderson  | 
wow signal
Jerry Ehman's original writing next to the sequence that seemed to suggest an extraterrestrial communication. Today it's known as the Wow! signal. SETI

Thanks to NASA's Kepler mission, astronomers have identified more than 5,000 exoplanets in our tiny corner of the Milky Way galaxy alone [source: NASA]. Multiply those 5,000 potentially inhabitable planets by the vastness of space and time, and it seems inconceivable that we are the only intelligent life-forms in creation (and this former intel official agrees).

The wow signal, a mysterious radio signal detected in 1977, has been a topic of intrigue and speculation among astronomers and enthusiasts alike.


Are We Alone in the Universe?

This tantalizing question is what launched the first serious scientific search for extraterrestrial intelligence (SETI) in the 1970s. In 1973, the Ohio State University Radio Observatory — known as "Big Ear" — began scanning the skies for the slightest traces of extraterrestrial transmissions, blips in the deafening silence of space [source: Kawa]. And on an August night in 1977, the first astonishing signal they received wasn't a whimper, but a roar.

Jerry Ehman, an Ohio State professor volunteering with the Big Ear SETI experiment that summer in 1977 [source: Krulwich], was no stranger to the data the telescope produced. Every couple of days, a bike messenger would arrive at Ehman's office with a pile of computer printouts generated by the telescope's mainframe computer. Ehman's thankless job was to scan the mind-numbing numbers for anomalies, anything that stood out from the constant low hum of background noise.


On Aug. 18, 1977, Ehman was scanning readouts from three days earlier when he came across something radically different. Instead of the usual 1s and 2s and occasional 4s, there was a stream of both letters and numbers signaling a radio transmission 30 times louder than the background buzz of deep space [source: Krulwich]. Grabbing a red pen — he was a teacher, after all — Ehman circled the mysterious sequence "6EQUJ5" and excitedly scribbled next to it a single word: "Wow!"

More than 35 years later, the so-called "Wow!" signal remains the "closest encounter" mankind has ever had with what may or may not be an extraterrestrial intelligence. The powerful blast of radio waves lasted just 72 seconds, but many astronomers and amateur ufologists believe the unique characteristics of the signal point to a celestial origin. In the decades since that original Wow! moment, no one has been able to replicate the signal or identify its definitive source, cosmic or Earthly.


How SETI Works

This diagram compares the planets of our inner solar system to Kepler-186, a five-planet star system about 500 light-years from Earth in the constellation Cygnus. The five planets of Kepler-186 orbit an M dwarf, a star that is half the size and mass of the sun. NASA/JPL-Caltech/T. Pyle

The Basics of SETI's Search

The nearest planet that is similar in size to Earth and located within the narrow habitable zone of its star is unromantically named Kepler-186f. If there is alien life on this planet, none of us will ever know. That's because Kepler-186f is 493 light-years away [source: NASA]. The search for extraterrestrial intelligence began with a focus on our own solar system before expanding its scope.

When the SETI began in the 1960s, astronomers quickly dismissed the idea of physically visiting an alien planet. The technological advances necessary to shoot humans across the galaxy is, like the nearest habitable planet, still light-years away.


Listening to the Heavens

Instead, the SETI sciences decided to stay on Earth, but keep an ear on the heavens. If intelligent life is out there, SETI decided, then it must have an understanding of radio waves and the electromagnetic spectrum.

Like us, the alien species probably doesn't have unlimited energy resources to travel around the universe looking for friends. The most efficient way to say, "Hello, universe. We're here!" is to send a radio transmission.

Choosing the Right Frequency

The next decision for SETI scientists was where to listen. The best guess was promoted by two Cornell physicists in the early 1960s, Philip Morrison and Guiseppi Cocconi. The two men assumed that an extraterrestrial life-form intelligent enough to master the electromagnetic spectrum would try to craft its message in a "common language" that anyone could understand [source: Selle].

The most common electromagnetic frequency, Morrison and Cocconi reasoned, is emitted by the most common element in the universe: hydrogen. If an alien signal from an extraterrestrial intelligence were to choose a single frequency to broadcast a long-range message, SETI scientists concluded, that's the one.

The Process of Scanning the Skies

And so began the search for alien life. Using large radio telescopes, astronomers focus on one tiny patch of sky and listen for the faintest sign of an unusual transmission coming over the 1420 MHz frequency. After listening for a few minutes, the telescope moves on to the next tiny patch of sky, and so on and so on [source: Andersen].

And that's exactly what Jerry Ehman and other SETI volunteers were doing with the Big Ear telescope at Ohio State back in the summer of 1977. They were listening to a sliver of the sky near the constellation Sagittarius and measuring the strength of the signal detected on the 1420 MHz channel.

Ehman and others had been at it for years, always receiving the same 1s and 2s of normal background radiation, until Aug. 15, when the Big Ear picked up a startling signal that would echo through the decades.


The Case for the 'Wow!' Signal

The Significance of the Hydrogen Line

For 72 seconds on Aug. 15, 1977, the Big Ear radio telescope picked up a signal that was 30 times as loud as the normal background noise. But what makes this signal worthy of Jerry Ehman's famous "Wow!"? Why does it look to many astronomers like a message from an alien planet?

First, it has to do with the hydrogen line. The frequency of the "Wow!" signal was recorded as 1420.4556 MHz, almost exactly the electromagnetic wavelength of hydrogen [source: Krulwich]. If an alien signal from an extraterrestrial intelligence were to choose a single frequency to broadcast a long-range message, SETI scientists concluded, that's the one.


The Shape of the Signal

The second striking characteristic of the "Wow!" signal is its "shape." The shapes of radio signals describe how they would look if graphed over time.

When the "Wow!" signal was first detected by Big Ear, it registered as a 6 on the telescope's "loudness" scale. A few seconds later, it jumped to an "E" (the computer could only report single digits, so when a number exceeded 9, it switched to letters). The signal peaked at "U" (the equivalent of the No. 30), then it slowly decreased back to 5. Plotting the signal on a graph, you get a nearly symmetrical pyramid shape.

Why the Signal's Shape Matters

Why does the signal's shape matter? Because it matches the shape you would expect from a deep space source. Here's why [source: Andersen]:

  • A radio telescope is located on Earth's surface.
  • As Earth's rotation occurs, the telescope's focal range slowly drifts across the radio sky.
  • If the origin of a radio signal is a fixed point in deep space, the signal will appear weak as it first enters the telescope's range.
  • When the telescope points straight at the source, the signal will be the loudest.
  • As the telescope drifts out of range of the signal, it decreases again, hence the pyramid shape.

Another intriguing feature of the "Wow!" signal is its sharpness. Most natural sources of radio waves, like stars and galaxies, emit a broad range of frequencies. But the "Wow!" signal was extremely narrow, suggesting it was produced by a man-made (or alien-made) transmitter.

The Signal's Location

The last piece of the puzzle is the signal's location. The Big Ear telescope was listening to a patch of sky near the constellation Sagittarius, which is located in the direction of the center of our galaxy. If you were an alien civilization trying to send a message to another intelligent species, you might choose to broadcast it toward the densest cluster of stars in the galaxy.


The Case Against the 'Wow!' Signal

wow signal
This shows the location of the Wow! signal on a star map. There are two possible regions indicated here; the ambiguity is due to the way in which the original 1977 experiment was designed. Benjamin Crowell/Wikimedia Commons (CC BY-SA)

The biggest argument against the "Wow!" signal being a message from an alien civilization is that no one has been able to replicate it. Since 1977, both amateur and professional astronomers have pointed their telescopes at the same patch of sky near Sagittarius thousands of times and have never picked up a similar signal. The Big Ear even scanned the same patch of sky 100 more times but found nothing [source: Gray and Marvel].

Robert Gray, an amateur astronomer and data analyst with a passion for the "Wow!" signal, conducted the most serious attempt to replicate the signal using one of the biggest and baddest radio telescopes on Earth, the Very Large Array (VLA) in New Mexico.


In 1995 and 1996, Gray aimed the VLA at Sagittarius, the first time the telescope was used expressly to search for signs of extraterrestrial life. The VLA — which combines the power of 27 separate radio antennas — is 100 times more sensitive than the Big Ear, which was retired in 1997 [sources: NRAO, Gray and Marvel]. Sadly, Gray found no trace of the "Wow!" signal with the VLA.

Possible Earthly Origins

There are many possible earthly explanations for the "Wow!" signal. It could have been a reflection of a terrestrial radio signal bouncing off a piece of space debris. Or it could have been a transmission from a secret military satellite. Or maybe it was just a glitch in the Big Ear's computer system.

The Signal's Short Duration

Another argument against the "Wow!" signal's extraterrestrial origins is its short duration. If an alien civilization were trying to get our attention, why would they send a message that lasted only 72 seconds and was never repeated?

The Signal's Strength

The strength of the "Wow!" signal is also a point of contention. If it was a message from an alien civilization, it would have to be incredibly powerful to reach us from such a great distance. Some scientists argue that the necessary power would be beyond the capabilities of even a Type II civilization on the Kardashev scale, which measures a civilization's technological advancement by the amount of energy it can harness [source: Krulwich].


The 'Wow!' Signal: A Continuing Cosmic Conundrum

The "Wow!" signal remains one of the most tantalizing mysteries in the search for extraterrestrial intelligence. While many astronomers and enthusiasts believe it was a genuine message from an alien civilization, others remain skeptical. The truth may never be known, but the "Wow!" signal continues to inspire and intrigue those who look to the stars and wonder if we are truly alone in the universe.


Lots More Information

Related Articles

  • Andersen, Ross. "The '"Wow!"' Signal: One Man's Search for SETI's Most Tantalizing Trace of Alien Life." The Atlantic. Feb. 16, 2012 (Feb. 4, 2015)
  • Caballero, Alberto. "An approximation to determine the source of the WOW! Signal." International Journal of Astrobiology. May 6, 2022. (May 27, 2022)
  • Gray, Robert H. and Marvel, Kevin B. "A VLA Search for the Ohio State 'Wow.'" The Astrophysical Journal. Jan. 10, 2001 (Feb. 4, 2015)
  • Kawa, Barry. "'Big Ear' designer a pioneer in field." Sept. 18, 1994. (May 27, 2022)
  • Krulwich, Robert. "Aliens Found in Ohio? The "Wow!" Signal." NPR. May 28, 2010 (Feb. 4, 2015)
  • NASA. "Exoplanet Exploration Program." (May 27, 2022)
  • NASA. "NASA's Kepler Discovers First Earth-Size Planet In The 'Habitable Zone' of Another Star." April 17, 2014. (May 27, 2022)
  • NASA. "NASA's Kepler Marks 1,000th Exoplanet Discovery, Uncovers More Small Worlds in Habitable Zones." Jan. 6, 2015 (Feb. 5, 2015)
  • National Radio Astronomy Observatory. "Welcome to the Very Large Array!" (Feb. 4, 2015)
  • Selle, Don. "The Wow! Signal." August 2012. (May 27, 2022)
  • "Humanity Responds to 'Alien' Wow Signal, 35 Years Later." Aug. 17, 2012 (Feb. 4, 2015)
  • Vergano, Dan. "Kepler Telescope Discovers Most Earth-Like Planet Yet." National Geographic. April 17, 2014 (Feb. 4, 2015)