The Wow! signal

The Wow! signal was a strong, narrowband radio signal detected by Dr. Jerry R. Ehman on August 15, 1977 while working on a SETI project at the Big Ear radio telescope of Ohio State University. The signal bore expected hallmarks of potential non-terrestrial and non-solar system origin. It lasted for 72 seconds, the full duration Big Ear observed it, but has not been detected again. It has been the focus of attention in the mainstream media when talking about SETI results. Amazed at how closely the signal matched 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. This comment became the name of the signal.

It has been speculated that interstellar scintillation of a weaker continuous signal — similar, in effect, to atmospheric twinkling—could be a possible explanation, although this still would not exclude the possibility of the signal being artificial in its nature. However, even by using the significantly more sensitive Very Large Array, such a signal could not be detected, and the probability that a signal below the Very Large Array level could be detected by the Big Ear radio telescope due to interstellar scintillation is low.Other speculations include a rotating lighthouse-like source or a signal sweeping in frequency.
Ehman has stated his doubts that the signal is of intelligent extraterrestrial origin: "We should have seen it again when we looked for it 50 times. Something suggests it was an Earth-sourced signal that simply got reflected off a piece of space debris."
He later recanted his skepticism somewhat after further research scientifically relegated an Earth-bound signal to be astronomically unlikely, due to the requirements of a space-borne reflector being bound to certain unrealistic requirements to sufficiently explain the nature of the signal. Also, the 1420 MHz signal is problematic in itself in that it is "protected spectrum" or bandwidth in which terrestrial transmitters are forbidden to transmit. In his most recent writings, Ehman resists "drawing vast conclusions from half-vast data."

Wow! signal - Wikipedia:

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