The Wow! Signal

The Big Ear telescope at Ohio State University had been scanning the sky for signs of intelligent life for several years when its equipment recorded an unusual burst of radio energy. Astronomer Jerry Ehman found it a few days later while reviewing printouts of the night's data. The signal appeared as the sequence "6EQUJ5," representing the intensity rising and falling over the observation window. Ehman circled it in red ink and wrote "Wow!" in the margin. The name stuck.

What made the signal remarkable wasn't just its strength but its specificity. It arrived at 1,420 megahertz, also known as the "hydrogen line"—the frequency at which neutral hydrogen naturally emits radiation. Scientists had long theorized that any civilization wanting to announce itself would broadcast at this frequency because it's universally recognizable to anyone who understands basic chemistry. The signal was also narrowband, meaning it occupied a tight range of frequencies more consistent with an artificial transmission than natural phenomena.

The 72-second duration wasn't a property of the signal itself but a limitation of the telescope. Big Ear was fixed in place and relied on Earth's rotation to scan the sky. Any source would remain in its field of view for exactly 72 seconds. The signal's intensity rose for 36 seconds as the telescope approached it, then fell for 36 seconds as it moved away, exactly matching the pattern an extraterrestrial beacon would produce.

Researchers have pointed the telescope back at that patch of sky hundreds of times. Nothing similar has ever appeared. The SETI project at Big Ear continued for 24 years and never recorded anything else like it. In 2020, some researchers proposed the signal might have originated from a cold hydrogen cloud in space, but not everyone is convinced.

The signal came from the direction of the constellation Sagittarius, about 120 light-years from Earth. Whatever caused it remains unknown.