On Aug. 15, 1977, Ohio State University's Big Ear radio telescope detected a 72-second radio burst in Sagittarius, known as the 'Wow!' signal. Its strength ruled out natural and earthly origins, but no similar signal has been found. The mystery endures as a landmark in the search for extraterrestrial life.
Mysterious 'Wow!' Signal Still Unexplained 49 Years On
Source: Space