The Wow Signal — 72-Second Transmission May Be Alien Contact

On August 15, 1977, astronomer Jerry Ehman was reviewing data from the Big Ear radio telescope at Ohio State University when he circled a sequence of numbers and wrote 'Wow!' in the margin. The signal lasted the full 72 seconds that the telescope was trained on that area of sky and displayed all the characteristics scientists had predicted an extraterrestrial signal would have. The signal came from the direction of the constellation Sagittarius and appeared to originate from outside the solar system. It was 30 times louder than the background noise of space, used a frequency very close to the hydrogen line at 1420 MHz—considered the most logical frequency for intelligent life to use for interstellar communication—and showed the natural rise and fall pattern expected from a signal coming from a fixed point in space. Despite repeated attempts to detect it again using the same and more powerful telescopes, the signal has never been heard again. In 2016 a team claimed the signal may have come from two comets near that position, but this explanation was disputed by astronomers who noted the comets' radio emissions were too weak. The Wow! signal remains the strongest candidate for extraterrestrial contact detected by SETI in its history. In 2012, a message was broadcast toward the signal's origin in response. It will take approximately 200 years to reach its destination.