From The Editor | September 7, 2023

The Wow! Signal: 72 Seconds That Still Remain A Mystery

John Headshot cropped  500 px wide

By John Oncea, Editor


The "Wow! signal" is the name given to a strong and unusual radio signal detected by Dr. Jerry R. Ehman on August 15, 1977. This signal was detected at Ohio State University's Big Ear radio telescope, which was used for the SETI program. The Wow! signal is notable for being one of the most famous and intriguing potential instances of a signal from an extraterrestrial civilization.

Pick your favorite time travel machine and journey with me to 1977. I’m going with Mr. Peabody’s WABAC Machine. You can have a Doc Brown’s DeLorean, Doctor Who’s TARDIS, or Bill and Ted’s phone booth. Heck, jump into the Hot Tub Time Machine if you want, just set the date to August 15 and the location to Delaware, OH. Specifically Ohio State University’s Radio Observatory, better known as the Big Ear.

It was there, at 11:16 p.m., that the radio telescope “received a startling radio signal,” writes Explorersweb.


A seemingly random sequence of numbers and letters that, in reality, “was a powerful radio signal from deep space whose origin remains unknown to this day. The best-known theory: It comes from an intelligent extraterrestrial source.”

Astronomer and Ohio State University (OSU) professor Dr. Jerry R. Ehman only saw the data afterward. When he poured over the pages, he found an intense signal that the computer printed as “6EQUJ5.” It lasted for 72 seconds, its intensity increasing for 36 seconds, then decreasing for 36 more as the telescope moved toward and away from the signal’s point of origin as the Earth rotated.

Nearly 50 years later, nobody can say for sure what happened that night at the Big Ear.

John Kraus And The Big Ear

The Big Ear was a large radio telescope located at OSU’s Perkins Observatory about 30 miles north of Columbus, OH. About the size of three football fields, it is to this day considered one of the most famous and historically significant radio telescopes in the field of radio astronomy.

Primarily used for conducting radio astronomy observations, particularly in the search for extraterrestrial intelligence (SETI), the telescope was built by John D. Kraus and his students starting in 1956. Construction was completed in 1961 and the telescope was turned on for the first time in 1963.

“Kraus was a member of the National Academy of Engineering, and won numerous awards including the Sullivant Medal from Ohio State in 1970 and the IEEE Edison Medal in 1985 ‘for a sustained career as an innovator, discoverer, and educator in the fields of antennas and radio astronomy.’” He also invented the helical antenna, which became the workhorse of space communication, and the corner-reflector used by millions for television reception.

The Big Ear is a Kraus-type radio telescope* that “reflected rays from a tiltable flat reflector panel onto a fixed parabolic rectangle, measuring 110 meters by 21 meters, which in turn, focused the signal to a central point at ground level,” notes OSU. “With the Big Ear, Kraus and colleagues studied some of the most distant known objects at the edge of the universe, and produced extensive surveys of the radio sky.”

An explanation of Big Ear on the Big Ear Memorial Website, Advanced Explanation - Not for the Astronomically-Challenged, describes how it worked as follows:

“The telescope was a ‘drift field’ design: that is, the rotation of the Earth scanned it in ‘right ascension’ or RA across the sky from west to east (so the sky looked like it was moving east to west). The flat tiltable reflector was adjusted to point to a position in the south along the ‘meridian’ line from south to north: that position was the ‘declination’ of the telescope.

“The part of the sky at the declination where the flat was ‘pointed’ reflected that area into the paraboloid 500 feet away; it focused that image back across 420 feet to the horn cart, where the horns ‘saw’ two areas 8 arc minutes wide by forty arc minutes tall. Over ten seconds, small areas were scanned in frequency as they ‘drifted’ by. One area was subtracted from the other to get rid of background noise including terrestrial noise and the sky background. This subtraction occurred by switching between the two beams at 79 Hz.

“The horn images were separated by about 40 arc minutes (about 150 seconds for a source on the celestial equator), so a distant point source would only be in one main beam at a time. The LOBES (LO-Budget Extraterrestrial_intelligence Search) program looked for ‘strikes’ to appear first in the east, then the west horn. When a strike was found, the narrow 10 kHz channel receiver was tuned to it. For a ‘strong’ SETI candidate, the 100 kHz scan was stopped, a 10 kHz scan was performed while the source was in the beam, and the horn cart moved to follow the source across the sky. Also, an ICOM communications receiver was tuned to the frequency of interest, and audio recordings were made using AM, FM, and SSB detectors.

“The Big Ear radio telescope was extremely sensitive. LOBES could detect in the continuum channel sources down to about 200 milliJanskys. For reference, the strongest stellar sources are ~2000 Janskys. Pulsars are a few Janskys but pulse too quickly for Big Ear to ‘count’ the pulses. The Sun is about a million Janskys. A Jansky is 10 to the minus 26 watts per square meter per Hertz.”

“The observatory completed the Ohio Sky Survey in 1971, and from 1973–1995, Big Ear was used to search for extraterrestrial radio signals, making it the longest-running SETI project** in history,” writes the Delaware County Historical Society. “The observatory was disassembled in 1998 when developers purchased the site from the university and used the land to expand (Delaware Golf Club).”

Though it has been gone for a quarter of a century, the Big Ear’s design concepts remain in use today at the Nançay Radio Telescope (NRT) located in France. NRT is four times as large as the Big Ear and is also the second-largest telescope in Europe (as well as the fifth-largest in the world).

The Big Ear holds a special place in the history of radio astronomy and the search for extraterrestrial life, and its contributions to these fields have left a lasting impact on our understanding of the universe and our quest to explore the possibility of life beyond Earth.

* “Kraus-type telescopes are transit instruments, where the flat primary mirror reflects radio waves toward the spherical secondary mirror, which focuses it toward a mobile focal carriage,” according to Wikiwand. “The primary tilts north–south to select any object near the meridian, while the focal carriage moves east–west along railroad ties to track objects near transit.”

** The Guinness Book of Records listed Big Ear under the category of Longest Extraterrestrial Search.*** At the time of the announcement, Robert Dixon, the Director of the Ohio SETI Program at Ohio State University, said “Some people think the whole search is baloney. But once a signal is found, it means something is out there – and it becomes the plum of the century.”

*** The record has since been broken by the SETI Institute.

6EQUJ5 = Wow!

The most famous event associated with the Big Ear was the detection of the “Wow! signal” on August 15, 1977. The Wow! signal was a strong narrowband radio signal detected by the telescope and lasted for 72 seconds. It remains one of the most intriguing and unexplained signals in the history of SETI, as it appeared to be a potential candidate for an extraterrestrial signal and got its name because of Ehman’s handwritten note in the margins of the data printout. When he saw the signal's distinctive pattern on the printout, he circled it and wrote "Wow!" next to it, hence its name.

Ehman’s explanation of why he wrote “Wow!” and circled the code is … intense. The most simplified explanation I came across started two decades before Ehman saw the code.

“Two physicists from Cornell had theorized that if aliens wanted to contact us, they would use radio signals due to their ability to travel vast distances easily and cheaply,” writes Mental Floss. “Furthermore, they said, ETs would likely send their message at 1420 megahertz, because hydrogen atoms resonate at that particular rate, and hydrogen is the most common element in the universe.

Every day, he would examine the letters and numbers that represented the strength of the electromagnetic signals received. He came across a remarkable occurrence – the signal he predicted to receive at 1420.4556 MHz was thirty times louder than any other surrounding noise. The signal lasted for 72 seconds, which was in line with the Earth's rotation. Moreover, it was a narrowband signal, indicating it was emitted by an intelligent source.

“To create a narrowband signal, you have to have some electronics to handle that. It’s not a natural phenomenon,” Ehman said.

“SETI scientists were able to trace the signal back to the constellation Sagittarius, northwest of the globular cluster M55, which contains about 100,000 stars,” Mental Floss writes. “But there was nothing there that could have made the signal. Puzzled, the scientists investigated other possibilities, including that the signal was a satellite transmission, a military signal, an aircraft signal, a broadcast beam, or even a beam that accidentally bounced off of space debris. None of it checked out, leaving ‘6EQUJ5’ a complete mystery.”

Despite extensive efforts to detect it again, the Wow! signal was never observed again. This lack of repeatability has added to its mystery and makes it challenging to definitively identify its source.

Numerous hypotheses have been proposed to explain the origin of the Wow! signal. Some suggest it could have been a natural celestial phenomenon or interference from Earth-based sources. The possibility of it being an intentional or unintentional radio signal from an extraterrestrial civilization also has been widely discussed.

The Wow! signal has been the subject of debate within the scientific community. While it's an intriguing and unexplained event, it does not constitute definitive evidence of extraterrestrial intelligence. Some scientists argue that more data is needed to draw any conclusions.

Astronomer Robert Gray called it “a tug on the cosmic fishing line. It doesn’t prove that you have a fish on the line, but it does suggest that you keep your line in the water at that spot.”

Despite its tantalizing nature, the Wow! signal remains a mysterious and unexplained event in the search for extraterrestrial intelligence. To date, no other signals quite like it have been observed, and its true origin remains a subject of speculation and curiosity in the field of astrobiology and SETI.

We Don’t Know What We Don’t Know

Several hypotheses have been proposed regarding the origin and characteristics of the Wow! signal, but none have been widely accepted, according to Discovery. One possible explanation could be interstellar scintillation of a weaker, continuous signal, which is similar to atmospheric twinkling. However, this does not rule out the possibility that the signal may be of artificial origin.

The Very Large Array, which is much more sensitive, did not pick up the signal. It is unlikely that the Big Ear would have been able to pick up a signal that was below the detection threshold of the Very Large Array due to interstellar scintillation. There are other potential explanations for the signal, including a source similar to a rotating lighthouse, a signal that changes in frequency, or a one-time burst.

Ehman said, in 1994, “We should have seen it again when we looked for it 50 times. Something suggests it was an Earth-sourced signal that simply got reflected off a piece of space debris.” After further research, he somewhat recanted his skepticism as it showed the unrealistic requirements needed for a space-borne reflector to produce the observed signal.

As of this writing, the source of the “Wow!” signal Ehman detected has not been identified. Recent suggestions that it could have been due to two comets that were passing in the vicinity of the position where the Big Ear telescope was pointing have not been widely accepted. New radio observations of a Sun-like star, previously believed to be the source of the WOW! signal, show no evidence of any signal-sending entities.

Whatever the cause, the Wow! signal has intrigued scientists and researchers for more than 40 years since the signal was first picked up. “If it was extraterrestrial intelligence that wanted to communicate with us,” asks Explorwers, “why hasn’t it happened again? Are they so far away that we will have to wait decades for another transmission? Or did we simply miss a very powerful cosmic event?”


Some experts believe that the likelihood of intelligent life existing beyond our planet is quite high. However, as of now, we are limited to a single event that may hold the answer to one of the most significant questions of humanity. Unfortunately, this event remains a dead-end curiosity that hasn’t provided us with any concrete answers yet.