Beyond the Veil Magazine

The Wow! Signal

Issue #17: May 1980

On 15 August 1977, astronomer Jerry Ehman was reviewing data from the Big Ear radio telescope at Ohio State University when he encountered something that made him circle the readings on the printout and write a single word in the margin: “Wow!”

He had detected a signal from deep space that appeared to be of intelligent origin.

The Signal

The Big Ear telescope, part of the SETI (Search for Extraterrestrial Intelligence) programme, had been scanning the skies for radio signals that might indicate the presence of intelligent life. Most of what it detected was noise: natural radio emissions from stars, galaxies, and the cosmic background.

The Wow! signal was different.

It lasted precisely 72 seconds, the maximum duration the telescope’s beam could observe a fixed point in space as the Earth rotated. It was a narrowband signal at 1420.456 MHz, very close to the hydrogen line at 1420.405 MHz. This frequency had long been considered the most likely choice for interstellar communication, as hydrogen is the most abundant element in the universe.

The signal was approximately 30 times stronger than the background noise. It rose in intensity over the first 36 seconds as the telescope’s beam centred on its source, then fell as the source moved out of the beam. This is exactly the pattern expected from a point source in space.

The signal appeared to originate from the constellation Sagittarius, in the direction of the star group Chi Sagittarii, approximately 120 light-years from Earth.

The Search for Repetition

In the days, months, and years following the detection, astronomers repeatedly pointed telescopes at the same region of sky, hoping to detect the signal again. They have been unsuccessful.

The Big Ear telescope itself observed the area over 50 times without detecting a repeat. Other instruments, including the Very Large Array, have searched without success.

This absence of repetition is puzzling. If the signal were a deliberate beacon from an intelligent civilisation, one would expect it to repeat. If it were a natural phenomenon, one would expect to detect similar signals from other sources.

Natural Explanations

Several natural explanations have been proposed:

Interstellar Scintillation: Radio signals passing through the interstellar medium can be amplified by plasma lensing effects. Perhaps a weak natural signal was temporarily boosted to detectable levels.

Comet Outgassing: Comets release hydrogen gas when heated by the sun. Some researchers have suggested that a comet passing through the telescope’s beam could have produced the signal. However, no comet was in the relevant position at the time.

Terrestrial Interference: Despite protocols to exclude Earth-based signals, some researchers suggest the signal might have been a reflection of a terrestrial transmission. This theory has been largely discounted by the signal’s characteristics.

Equipment Malfunction: The telescope may have produced a spurious reading. However, the signal’s pattern is precisely what would be expected from a genuine celestial source.

Artificial Explanations

If the signal was artificial, what might it have been?

Deliberate Contact Attempt: An intelligent civilisation might have transmitted a signal intended to attract attention. The choice of the hydrogen frequency suggests deliberate selection of a channel that other civilisations would monitor.

Leakage: Just as Earth’s radio and television transmissions leak into space, an advanced civilisation might produce detectable radio emissions without intending to communicate. The Wow! signal might have been incidental rather than deliberate.

One-Time Event: Perhaps the signal represented a unique event: a civilisation making a single transmission for unknown reasons, or an accident that produced a brief radio burst.

The Mystery Endures

Three years later, the Wow! signal remains unexplained. It is the strongest candidate for an extraterrestrial transmission ever detected, yet it has never repeated.

Jerry Ehman has remained undecided about the signal’s origin, declining to draw firm conclusions while maintaining that it was an extraordinary signal not produced by any known natural phenomenon.

The debate continues. Sceptics point to the absence of repetition as evidence against an artificial origin. Believers note that we have no reason to assume extraterrestrial civilisations would transmit continuously.

What is certain is this: for 72 seconds on a summer evening in 1977, something sent a signal from the direction of Sagittarius that, to this day, we cannot explain.

Was someone calling? We may never know.

Readers with expertise in radio astronomy or SETI research who may have insights into the Wow! signal are invited to contact our research department.