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For just 72 seconds on the night of August 15, 1977, a radio telescope in rural Ohio picked up one of the most extraordinary signals ever recorded, and it wasn't an ordinary burst of radio noise or a familiar astronomical source. Instead, it was an unusually strong, narrowband signal arriving from the direction of the constellation Sagittarius, close to the 1,420 MHz hydrogen line, a frequency long considered one of the most likely channels an intelligent civilization might use to communicate across interstellar distances. |