In 1967, a graduate student named Jocelyn Bell discovered something strange emanating from a region of the sky known as the Summer Triangle: pulses of radio waves repeating every 1.3373 seconds over and over again like a clock ticking slightly-slowly. 

It’s not every day that you find a nearly perfect clock ticking at you from the sky, so Bell and her colleagues half-jokingly called the source of the signal “LGM1”—the “LGM” being short for “Little Green Men.” We now know that this signal wasn’t from little green anythings, but was instead from a previously undiscovered type of object known as a pulsar. This was exciting, although perhaps not quite as exciting as finding aliens.

A decade later, an even stranger signal fell upon a different radio telescope. This signal was unusual in many ways: it was very strong, it didn’t look like any known naturally occurring radio signal, and it seemed to be coming from “out there” (and not here on Earth). The signal was so striking that its discoverer famously wrote the word “Wow!” on the margin of a printout of the data. After ruling out obvious Earthly origins, most astronomers are convinced that the signal came from somewhere beyond Earth. The question—which still remains unanswered—is where? And from what or whom? Was the signal produced by a natural phenomena? Or might it have been broadcast by some alien intelligence?


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