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The Wow! signal was a strong narrowband radio signal detected on August 15, 1977, by Ohio State University's Big Ear radio telescope in the United States, then used to support the search for extraterrestrial intelligence.

The signal appeared to come from the direction of the constellation Sagittarius and bore expected hallmarks of extraterrestrial origin. Ehman discovered the anomaly a few days later while reviewing the recorded data. On the computer printout, he circled the reading of the signal's intensity, "6EQUJ5", and wrote the comment "Wow!" beside it, leading to the event's widely used name. The entire signal sequence lasted for the full 72-second window during which Big Ear was able to observe it. Despite numerous follow-up searches and hypotheses (including brief consideration of reflections from space debris, interstellar scintillation, and comet hydrogen clouds), the signal has never recurred, and no explanation, terrestrial or otherwise, has been confirmed. The Wow! signal has inspired targeted searches, scientific discussion about rare astrophysical phenomena, and references in popular culture.

When Ehman computed the frequency of the Wow! signal, he took this error into account.

The Wow! signal had a bandwidth of less than 10 kHz. The Wow! signal is essentially confined to one column.

A continuous extraterrestrial signal, therefore, would be expected to register for exactly 72 seconds, and the recorded intensity of such a signal would display a gradual increase for the first 36 seconds—peaking at the center of the observation window—and then a gradual decrease as the telescope moved away from it. All these characteristics are present in the Wow! signal.

The Wow! signal was detected in one beam but not in the other, and the data was processed in such a way that it is impossible to determine which of the two horns received the signal.

Interstellar scintillation of a weaker continuous signal—similar in effect to atmospheric twinkling—could be an explanation, but that would not exclude the possibility of the signal being artificial in origin. The significantly more sensitive Very Large Array did not detect the signal, and the probability that a signal below the detection threshold of the Very Large Array could be detected by the Big Ear due to interstellar scintillation is low. In a 2019 interview with John Michael Godier, Ehman stated: "I'm convinced that the Wow! signal certainly has the potential of being the first signal from extraterrestrial intelligence." METI president Douglas Vakoch told Die Welt that any putative SETI signal detections must be replicated for confirmation, and the lack of such replication for the Wow! signal means it has little credibility. In August 2024, the Planetary Habitability Laboratory published a preprint reporting observations made in 2020 at the Arecibo Observatory in Puerto Rico, where they conclude that the Wow! signal was likely caused by a rare astrophysical event, in which stellar emissions energizing a cold hydrogen cloud caused it to suddenly surge in brightness.

Petersburg College, Florida, proposed that the hydrogen cloud surrounding two comets, 266P/Christensen and 335P/Gibbs, now known to have been in the same region of the sky, could have been the source of the Wow! signal.

Paul Shuch made several drift-scan observations of the Wow! signal's coordinates with a 12-meter radio telescope at the National Radio Astronomy Observatory in Green Bank, West Virginia, also achieving a null result. In 1995 and 1996, Gray again searched for the signal using the Very Large Array, which is significantly more sensitive than Big Ear.

In 2012, on the 35th anniversary of the Wow! signal, the Arecibo Observatory was said to have beamed a digital stream towards Hipparcos 34511, 33277, and 43587. None of the targeted stars is within the possible region from which the Wow! signal came.

The signal was featured in the 2024 television series 3 Body Problem, in which the signal is also detected in Inner Mongolia.

Quick Facts

• The Wow! signal has inspired targeted searches, scientific discussion about rare astrophysical phenomena, and references in popular culture.
• In a 2019 interview with John Michael Godier, Ehman stated: "I'm convinced that the Wow! signal certainly has the potential of being the first signal from extraterrestrial intelligence."
• The significantly more sensitive Very Large Array did not detect the signal, and the probability that a signal below the detection threshold of the Very Large Array could be detected by the Big Ear due to interstellar scintillation is low.
• The Wow! signal was detected in one beam but not in the other, and the data was processed in such a way that it is impossible to determine which of the two horns received the signal.
• The signal appeared to come from the direction of the constellation Sagittarius and bore expected hallmarks of extraterrestrial origin.

Source material: Wikipedia - "Wow! signal". Adapted and summarized for DiscoverScroll. Original contributors are credited through the linked Wikipedia article. Read original on Wikipedia. CC BY-SA 4.0. Changes were made from the original.