On August 15th 1977, a radio telescope located at Ohio State University detected something strange. The telescope was scanning the stars searching for possible signals from alien civilizations as part of the SETI project, and on that date it found something. The telescope recorded an incredibly strong signal appearing to come from somewhere in the direction of Sagittarius; the signal only lasted about a minute and was never detected again.

The signal was so strong that astronomer Jerry Ehman, who first spotted it, circled it in red pen and wrote "Wow!" in the margin. The "Wow! signal," as it would come to be known, became the best evidence ever obtained for extraterrestrial life.

At least, until now. One astronomer believes he's figured out what really caused the Wow! signal and—spoiler alert—it's not aliens.

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