The SETI (Search for Extraterrestrial Intelligence) Institute is easily the most well-known observatory for alien life. Since being founded in 1984, they’ve grown from a two-person NASA offshoot project to a 100-employee, multidisciplinary education-and-research center overseen by trustees as such as astronomical titans Carl Sagan and Frank Drake, as the SETI website explains. Their search focuses on “narrow-band signals,” which use only “a small part of the radio spectrum” — a few hertz wide or less — produced by artificial transmitters, per the SETI FAQ. Natural celestial bodies such as large gaseous bodies, pulsars, quasars, and the like don’t generate these kinds of wavelengths.

Back in the summer of 1977, though, it wasn’t the SETI Institute prowling the skies in search of alien life. It was volunteers and nigh-broke university staff at the Big Ear Radio Observatory at Ohio State University. The observatory was a strange, unconventionally built, sky-mapping array constructed in the late 1960s on a “shoestring budget,” as former volunteer Jerry Ehman told Astronomy Magazine. Ehman was the one who sat down on August 17 to review data collected from the previous few days; just another volunteer session. What he discovered, though — a super strong signal from the constellation Sagittarius — stunned him so much that he circled his printout in red and wrote “Wow!” (above). Hence the moniker of the now-infamous, still-unexplained “Wow! Signal.” 

The 72-second long signal read “6EQUJ5,” indicating it started low, gained in strength, and then dropped off again. It was artificial, not from Earth, and has never been rediscovered.