Wow! signal
He was so impressed by the result that he circled on the computer printout the reading of the signal's intensity, "6EQUJ5", and wrote the comment "Wow!"
[2] The entire signal sequence lasted for the full 72-second window during which Big Ear was able to observe it, but has not been detected since, despite many subsequent attempts by Ehman and others.
In a 1959 paper, Cornell University physicists Philip Morrison and Giuseppe Cocconi had speculated that any extraterrestrial civilization attempting to communicate via radio signals might do so using a frequency of 1420 megahertz (21-centimeter spectral line), which is naturally emitted by hydrogen, the most common element in the universe and therefore likely familiar to all technologically advanced civilizations.
[3] In 1973, after completing an extensive survey of extragalactic radio sources, Ohio State University assigned the now-defunct Ohio State University Radio Observatory (nicknamed "Big Ear") to the scientific search for extraterrestrial intelligence (SETI), in the longest-running program of this kind in history.
[5] By 1977, Ehman was working at the SETI project as a volunteer; his job involved analyzing by hand large amounts of data processed by an IBM 1130 computer and recorded on line printer paper.
While perusing data collected on August 15 at 22:16 EDT (02:16 UTC), he spotted a series of values of signal intensity and frequency that left him and his colleagues astonished.
The result for each frequency channel was output on the printout as a single alphanumeric character, representing the 10-second average intensity, minus the baseline, expressed as a dimensionless multiple of the signal's standard deviation.
[2][9] John Kraus, the director of the observatory, gave a value of 1420.3556 MHz in a 1994 summary written for Carl Sagan.
[10] At the time of the observation, the Big Ear radio telescope was only adjustable for altitude (or height above the horizon), and relied on the rotation of the Earth to scan across the sky.
[13][14] The precise location in the sky where the signal apparently originated is uncertain due to the design of the Big Ear telescope, which featured two feed horns, each receiving a beam from slightly different directions, while following Earth's rotation.
[7] In 2022, a paper published in the International Journal of Astrobiology identified three likely Sun-like stars within the antenna-pointed coordinates.
[25] Interstellar scintillation of a weaker continuous signal—similar in effect to atmospheric twinkling—could be an explanation, but that would not exclude the possibility of the signal being artificial in origin.
[26][failed verification] Other hypotheses include a rotating lighthouse-like source, a signal sweeping in frequency, or a one-time burst.
"[27] He later somewhat recanted his skepticism, after further research showed the unrealistic requirements that a space-borne reflector would need to have to produce the observed signal.
[33] In August 2024, the Planetary Habitability Laboratory published a preprint reporting observations made in 2020 at the Arecibo Observatory in Puerto Rico—where they conclude that the Wow!
[34][35] In 2017, Antonio Paris, Assistant Professor of Astronomy and Astrophysics at St. Petersburg College, Florida,[36] proposed that the hydrogen cloud surrounding two comets, 266P/Christensen and 335P/Gibbs, now known to have been in the same region of the sky, could have been the source of the Wow!
[37][38][39] This hypothesis was dismissed by astronomers, including members of the original Big Ear research team, as the cited comets were not in the beam at the correct time.
[26][43][page needed] In a July 1995 test of signal detection software to be used in its upcoming Project Argus, SETI League executive director H. Paul Shuch made several drift-scan observations of the Wow!
[47] To increase the probability that any extraterrestrial recipients would recognize the signal as an intentional communication from another intelligent life form, Arecibo scientists attached a repeating-sequence header to each individual message, and beamed the transmission at roughly 20 times the power of the most powerful commercial radio transmitter.
