The Wow! signal was a strong narrowband radio signal detected by Jerry R. Ehman on August 15, 1977, while he was working on a SETI project at the Big Earradio telescope of The Ohio State University, then located at Ohio Wesleyan University's Perkins Observatory in Delaware, Ohio. The signal bore the expected hallmarks of non-terrestrial and non-Solar System origin. The signal appears to have come from the northwest of the globular cluster of M55 in the constellationSagittarius, near the Chi Sagittarii star group.

The entire signal sequence lasted for the full 72-second window that Big Ear was able to observe it, but has not been detected again. The signal has been the subject of significant media attention, and astronomers have tried many times in vain to find the signal again. Impressed by the relative resemblance of the expected signature of an interstellar signal in the antenna used, Ehman circled the signal on the computer printout and wrote the comment "Wow!" on its side, which became the name of the signal itself