On a muggy August night in 1977, a strip of computer printout rolled out of a machine at Ohio State University’s Big Ear radio telescope, and astronomer Jerry Ehman did something almost no scientist ever gets to do.

He grabbed a red pen, circled six characters on the page, and wrote a single word in the margin that would echo across decades: Wow!

“1 1 1 1 1 1 2 3 4 6 E Q U J 5 4 3 2 1 1 1 1 1 Wow!” — J. Ehman Aug 1977

Those six alphanumeric characters 6EQUJ5 represented a 72-second blast of radio energy arriving at exactly 1420.405 megahertz, the so-called hydrogen line. This is the frequency that scientists had long theorised an intelligent civilisation might use to broadcast across the cosmos, because hydrogen is the most abundant element in the universe and any space faring species would know it. The signal was precisely what the Search for Extraterrestrial Intelligence had dreamed of finding. It arrived. It dazzled. Then it was gone.

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