Wow!: The Signal from Sagittarius

On the evening of Monday the 15th of August 1977, in a field outside the small town of Delaware, Ohio, a radio telescope the size of three football fields was listening to the sky. There were no astronomers present. The telescope could not be steered. It sat on the ground, pointed straight up, and let the rotation of the Earth do its work for it. As the planet turned, patches of the night sky drifted, slowly, across its stationary field of view. At approximately 22:16 that evening, the telescope was scanning a patch of sky in the constellation Sagittarius. At that moment, a signal reached it. It was narrow. It was strong. It was almost exactly at 1420 megahertz, which is the natural emission frequency of neutral hydrogen. The hydrogen line. The frequency that in 1959, two physicists at Cornell University had predicted, in the pages of the journal Nature, would be the exact frequency that any alien civilisation trying to contact humanity would logically choose. The signal rose in intensity over 36 seconds. It peaked at approximately 30 times the background noise of the surrounding cosmos. Then it fell in intensity over the following 36 seconds. And then, at 22:17, it was gone. Three days later, a former physics professor named Jerry Ehman, working at the observatory as an unpaid volunteer, sat down at his desk to review the printouts. He found a vertical column of numbers and letters that made him take his red ballpoint pen, circle the sequence, and write, in the margin, a single word. Wow! It is, as of 2026, the closest thing that any radio telescope on Earth has ever recorded to the exact kind of signal that scientists have, since 1959, expected an alien civilisation to send. It has never, in the 48 years since it was detected, been observed again.

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