The Wow! signal: 72 seconds of transmission from space that no one has repeated or explained
A strong, narrowband radio signal at the frequency of hydrogen. It lasted 72 seconds in 1977 and was never picked up again.
- When
- August 15, 1977
- Where
- Big Ear radio telescope, Ohio, United States
- Status
- Open no accepted explanation yet
By The Echoes of the Past team. Published November 2, 2026. 4 min read.
In August 1977, astronomer Jerry Ehman was going through printed data from the Big Ear radio telescope at Ohio State University. Big Ear was part of the SETI project (Search for Extraterrestrial Intelligence), which listened to space for transmissions that could not be explained by known natural phenomena.
Ehman came across a string of characters in one of the data columns, recorded on August 15. It was a high-intensity radio signal at a specific frequency, with features that matched exactly what SETI theorists described as the kind of transmission an extraterrestrial civilization might use to be detected.
In the margin of the paper, Ehman wrote: "Wow!"
The signal lasted 72 seconds, the maximum time Big Ear could observe any point in the sky in a single sweep. It was never detected again.
What made the signal exceptional
The Wow! signal was unusual in several ways at once:
Frequency: The signal was detected at 1,420 MHz, the emission frequency of neutral hydrogen, the most abundant element in the universe. Theoretical physicists had suggested decades earlier that this would be the obvious frequency for technological civilizations to use for interstellar transmissions, because it is universally recognizable to any civilization with radio telescopes. By that reasoning, it is exactly the kind of signal a technological civilization would use to announce itself, which is why the case matters to anyone discussing the Fermi paradox.
Intensity: The signal was 30 times stronger than the background noise of space. That is extraordinary: most known natural radio signals are much weaker.
Narrow bandwidth: The signal occupied an extremely narrow frequency band, narrower than that of any known natural source. Natural radio sources (stars, pulsars, gas clouds) produce emissions across wide bands. Deliberate transmissions of technological origin are typically narrowband.
Pattern: The signal showed the variation in intensity expected from a point source in the sky being swept by the telescope (rising, peaking, falling), consistent with a distant, fixed source.
The searches and the silence
Since 1977, the spot in the sky where the Wow! signal came from has been observed hundreds of times by several radio telescopes around the world. The signal has never repeated.
That is a problem for any hypothesis, the extraterrestrial one included. If a civilization was transmitting a signal, why did it transmit only once? Or why did it transmit only in the direction we could detect, in that 72-second window?
A hypothesis put forward in 2017 by astronomer Antonio Paris suggested that the signal might have been caused by comets passing through that region of the sky in 1977. The hypothesis was challenged by other researchers, including Jerry Ehman himself, who argued that the signal's features were not consistent with emission from a comet.
In 2020, using a far more powerful radio telescope, SETI researchers scanned the region the signal came from and found nothing.
What the Wow! signal represents
The Wow! signal remains the most serious candidate for a signal of non-natural origin in the history of SETI. It is not confirmed. It has not been replicated. But it has never been adequately explained by any known natural source either.
It is, essentially, a one-time event with features consistent with what we would expect from a technological transmission, but which, because it never repeated, cannot be confirmed as one.
Jerry Ehman, who lived to see decades of fruitless searching for the signal, was consistently cautious in his statements: "I am not claiming it is an extraterrestrial transmission. I am claiming it was the most interesting signal we have ever detected and that we have no satisfactory explanation for it."
That honesty about what we do not know is the only kind of responsible statement the Wow! signal allows. It is the opposite of what happened in Mexico's Zone of Silence, where real electromagnetic anomalies were quickly swallowed up by interpretations that went beyond the available data.
And it is still there in the record: 72 seconds of something we cannot explain, in 1977, coming from somewhere in the constellation Sagittarius.
For other events where the sky was the stage for the unexplained, read about the Tunguska event and the 1942 Battle of Los Angeles. For the broader context of why the silence of the universe is so unsettling, see the Fermi paradox. For a coded message no one can decipher here on Earth, see the Voynich manuscript.
