On August 15, 1977, a volunteer astronomer named Jerry Ehman was reviewing data from Ohio State University’s Big Ear radio telescope when he noticed something extraordinary. A narrow-band radio signal had arrived from the direction of the constellation Sagittarius — a signal so remarkable in its characteristics that Ehman circled it on the computer printout and wrote a single word in red pen: “Wow!” Nearly five decades later, that signal has never been explained, never been repeated, and remains the strongest candidate for extraterrestrial contact in the history of SETI research.
What Exactly Was the Wow! Signal?
The Big Ear telescope was operating as part of SETI — the Search for Extraterrestrial Intelligence — scanning the sky for unusual radio emissions. On that August evening, it detected a signal lasting 72 seconds that displayed exactly the characteristics scientists had predicted an extraterrestrial transmission might show. The signal appeared at 1420.4056 MHz, the emission frequency of neutral hydrogen — the most abundant element in the universe and the frequency SETI researchers had long theorized an intelligent civilization would use for interstellar communication precisely because any technologically advanced species would know about it.
The signal’s intensity pattern — rising and falling in a characteristic bell curve as the telescope’s fixed beam swept across it — matched precisely what a fixed point source in deep space would produce. It was 30 times stronger than the background noise of space. It had no detectable bandwidth. It came from a direction consistent with the globular cluster M55 in Sagittarius or, in some analyses, empty interstellar space in the same general direction. And then it was gone, never to return.
The Search for a Repeat Signal: Decades of Listening
In the 47 years since the Wow! signal was detected, astronomers have pointed every major radio telescope on Earth at the same region of sky during the same time windows in hopes of detecting a repeat. Big Ear itself made over 50 follow-up observations of the source region before the telescope was demolished in 1998. The Arecibo Observatory, the world’s largest single-dish radio telescope at the time, conducted extensive surveys of the same sky coordinates. The Very Large Array in New Mexico, the Parkes Observatory in Australia, and dozens of other facilities around the world have all attempted to capture the signal again. None has succeeded.
The failure to repeat the signal is both frustrating and scientifically significant. It rules out most conventional terrestrial or near-Earth sources — a satellite, an aircraft, or local interference would almost certainly reappear. It also complicates the extraterrestrial interpretation: if the signal was a deliberate transmission from another civilization, why send it only once? Some theorists propose it may have been a directional transmission that swept past Earth like a lighthouse beam, and that we simply haven’t been in its path again. Others suggest the transmitting civilization may have stopped broadcasting, or that the signal was a one-time event — a technological accident or a natural phenomenon we don’t yet understand.
Alternative Explanations: What Else Could It Have Been?
Over the decades, scientists have proposed several non-extraterrestrial explanations for the Wow! signal, none of which has gained universal acceptance. In 2017, astronomer Antonio Paris proposed that the signal may have been generated by a hydrogen cloud surrounding one or two comets — 266P/Christensen and P/2008 Y2 (Gibbs) — that were in the vicinity of the source coordinates at the time. This explanation attracted significant media coverage but was quickly criticized by other astronomers, who pointed out that comets do not emit radio waves at the 1420 MHz hydrogen line and that Paris’s orbital calculations were disputed.
Other proposed explanations include: a terrestrial signal reflected off space debris (ruled out due to the signal’s characteristics), a natural astrophysical phenomenon not yet catalogued (possible but unidentified), and even a classified military satellite (impossible to confirm or deny). The original interpreter, Jerry Ehman himself, maintained until his later years that the signal’s characteristics so perfectly matched theoretical predictions for an extraterrestrial transmission that no natural or man-made source had ever adequately explained it. “The most plausible explanation,” he wrote, “is that the signal was of extraterrestrial intelligent origin.”
The Response to Wow!: Humanity Sends a Message Back
In August 2012 — exactly 35 years after the original signal — a group of scientists transmitted a reply toward the source coordinates of the Wow! signal. Using the Arecibo Observatory, they beamed a digital message containing 10,000 Twitter responses, several scientific formulas, and greetings in multiple languages. The transmission was organized by the National Geographic Channel and was largely symbolic rather than scientifically rigorous, but it represented humanity’s first deliberate attempt to respond to the Wow! signal. Any reply from the source, traveling at the speed of light, would not arrive back on Earth for at minimum 48 years from the time of our transmission — and that assumes the original signal actually came from a civilization only 24 light-years away.
Why the Wow! Signal Still Matters Today
The Wow! signal occupies a unique position in the history of scientific inquiry. It is the only signal in 60+ years of SETI research that has ever been considered a serious candidate for non-human intelligent origin by mainstream astronomers. It meets every criterion that SETI researchers identified as signatures of an intentional interstellar transmission. And it has never been explained. In a field where the absence of confirmed contact tempts researchers and the public alike to either give up or resort to wishful thinking, the Wow! signal stands as a genuine, documented anomaly — a 72-second measurement from 1977 that science has not been able to explain away and has not been able to explain forward. It remains, in every meaningful sense, the best evidence we have that we may not be alone — and the most maddening evidence, because it arrived once, left no forwarding address, and has never come back.
Sources and Further Reading
- Ehman, J.R. (1997). “The Big Ear Wow! Signal: What We Know and Don’t Know About It After 20 Years.” The Big Ear Radio Observatory.
- Dixon, R.S. & Cole, D.M. (1977). “A Search for Extraterrestrial Radio Signals.” Ohio State University Radio Observatory.
- Paris, A.B. et al. (2017). “Hydrogen Line Observations of Cometary Spectra at 1420 MHz.” Journal of the Washington Academy of Sciences, 103(2).
- SETI Institute: seti.org
- Big Ear Radio Observatory archive: bigear.org
Discover more from Infinity Explorers
Subscribe to get the latest posts sent to your email.