The Wow! Signal

On August 15, 1977, a radio telescope at Ohio State University detected a signal from deep space that matched what scientists expected from an extraterrestrial transmission. Astronomer Jerry Ehman, reviewing the data printout three days later, circled the alphanumeric sequence and wrote “Wow!” in the margin. The signal has never been detected again, and despite decades of investigation, its source remains one of the great unsolved mysteries of the search for extraterrestrial intelligence.

The Big Ear

The Big Ear radio telescope was part of Ohio State University’s Search for Extra-Terrestrial Intelligence (SETI) project. It scanned the sky for narrow-band radio signals that might indicate intelligent origin—signals that would be distinct from the broad-band noise produced by natural astronomical sources.

On August 15, 1977, the telescope detected a signal in the 1420 MHz hydrogen line—a frequency considered promising for interstellar communication because hydrogen is the most common element in the universe and this frequency is relatively free of natural interference.

The Signal

The Wow! signal lasted 72 seconds, which matched the expected length for a signal from a fixed point in space as the Big Ear swept across the sky. The signal was 30 times stronger than background noise and showed the narrow-band characteristics expected of an artificial transmission.

The alphanumeric code “6EQUJ5” represented the signal’s intensity over time, with letters representing higher values than numbers. The “U” in the middle represented an intensity 30 times the normal background—an exceptionally strong signal.

The Search for an Explanation

Astronomers have proposed numerous explanations for the Wow! signal, none entirely satisfactory.

The signal did not come from Earth or known satellites. It appeared to originate from the direction of the constellation Sagittarius, near the globular cluster M55.

Despite numerous attempts, the signal has never been detected again from that location. The Big Ear and other radio telescopes have searched repeatedly, finding nothing.

Some astronomers have proposed that the signal could have been caused by a comet, whose hydrogen coma might produce a signal at 1420 MHz. However, this theory is controversial—a comet would need to be exactly positioned and of unusual composition to produce such a strong, brief signal.

Other proposed explanations include an interstellar hydrogen cloud, equipment malfunction, or terrestrial interference reflected from space debris. None fully explains all characteristics of the signal.

The Extraterrestrial Hypothesis

The possibility that the Wow! signal was genuinely extraterrestrial cannot be dismissed. It matched the profile expected of an artificial transmission. It came from deep space. It has never been explained by natural phenomena or human technology.

However, a single unrepeatable signal is poor evidence for alien intelligence. A genuine attempt at interstellar communication would likely be repeated and would likely include more information content than the Wow! signal displayed.

Legacy

The Wow! signal remains the strongest candidate for an extraterrestrial radio signal ever detected. It has become iconic in SETI history, inspiring continued searches and endless speculation.

The Big Ear telescope was demolished in 1998 to make way for a golf course. Its most famous discovery remains unexplained.

Assessment

The Wow! signal may have been:

• A transmission from an extraterrestrial intelligence
• An unknown natural phenomenon
• An equipment artifact or processing error
• An unusual terrestrial signal reflected from space

Without repetition or additional data, we cannot determine which explanation is correct. The signal endures as a tantalizing mystery—a 72-second transmission from the cosmos that may have been nothing at all, or may have been humanity’s closest brush with proof that we are not alone.