An Unexpected Spike in the Cosmos
On August 15, 1977, a routine scan by Ohio State University’s Big Ear radio telescope recorded something no one had seen before: a strong, narrowband radio signal coming from the direction of the constellation Sagittarius.
A few days later, astronomer Jerry R. Ehman circled the data—specifically the string “6EQUJ5”—and scribbled “Wow!” in the margin. The mysterious signal lasted exactly 72 seconds, the maximum duration the fixed-position Big Ear could observe a single point in the sky. It has never been detected again, despite numerous follow-up efforts.
What the Telescope Saw
The Big Ear telescope was tuned to monitor frequencies near 1420 megahertz—the natural emission line of hydrogen, chosen because it was considered a likely frequency for interstellar communication. The Wow! signal peaked at “U” on the observatory’s intensity scale, indicating a signal strength 30 times greater than background noise.
It was narrowband, consistent with artificial origins, and followed the expected time profile of a fixed-point source. The signal appeared in only one of Big Ear’s two feed horns, making it impossible to determine which of two sky coordinates it came from.
A Search Without an Echo
Following the initial detection, Ehman and others repeatedly searched the same area for a repeat of the signal. None came. Later searches in the 1980s and 1990s by astronomers like Robert Gray and Simon Ellingsen, using instruments including the Very Large Array and the Mount Pleasant Radio Observatory in Tasmania, failed to detect any similar emissions.
In 2022, the Breakthrough Listen project targeted the same coordinates using the Green Bank Telescope and the Allen Telescope Array. Again, no signal was found.
Theories, Debates, and Ongoing Interest
Over the decades, scientists have suggested explanations ranging from reflected Earth signals to astronomical phenomena. One 2017 hypothesis claimed the signal came from hydrogen clouds around comets, but this was refuted because the comets weren’t in the correct location at the time and don’t emit strongly at that frequency.
In 2024, researchers proposed the signal may have been caused by a rare event involving a cold hydrogen cloud energized by stellar emissions. Meanwhile, in 2012, a commemorative signal was beamed toward the stars from the Arecibo Observatory, made up of 10,000 Twitter messages. Although the Wow! signal has never repeated, it remains the strongest candidate for a detected extraterrestrial radio transmission.
Ehman himself later said that the signal still had “the potential of being the first signal from extraterrestrial intelligence.” However, due to the lack of replication, it remains an open and unsolved case in radio astronomy.
In 1977, a powerful narrowband radio signal was detected by Ohio State University’s Big Ear telescope, pointing toward the constellation Sagittarius.
The signal lasted 72 seconds, fit expected extraterrestrial characteristics, and has never been detected again…🧵👇 pic.twitter.com/gIPNxNrC92
— Detective Tiger’s Stories (@TigerDetective) July 7, 2025