Astronomer Jerry R. Ehman found the signal a few days after it was received while reviewing the data printout. He was so impressed by it that he circled the text that represented the signal on the computer printout, "6EQUJ5", and wrote the comment "Wow!" on its side, leading to the event's widely used name.
The entire signal was detected for the full 72-second window during which Big Ear was able to observe it, but has not been detected since, even though many, such as Ehman, have tried to. Many explanations have been given on where the signal comes from, including natural and human-made sources, but none of them are good enough to explain the signal.
Although the Wow! signal had no detectable changes which would have allowed the signal send information, it remains the strongest candidate for an alien radio transmission ever detected.
In a 1959 paper, Cornell University physicists Philip Morrison and Giuseppe Cocconi made an educated guess that any extraterrestrial civilization trying to communicate with radio signals might do so using a frequency of megahertz ( centimeters), which is naturally emitted by hydrogen, which is the most common element in the universe, and is likely familiar to all technologically advanced civilizations.
In 1973, after completing a survey of radio sources coming from other galaxies, Ohio State University assigned the 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. The radio telescope was located near the Perkins Observatory on the campus of Ohio Wesleyan University in Delaware, Ohio.
By 1977, Ehman was working at the SETI project as a volunteer; his job involved going through (by hand) large amounts of data processed by a computer and recorded on paper. While looking at data collected on August 15 at 22:16 EDT (02:16 UTC), he noticed a series of values of showing signal strength and frequency that left him and people he was working with amazed.
The event was later documented in detail by the observatory's director.
The string 6EQUJ5 is commonly misunderstood as a message encoded in the radio signal. This string actually represents the signal's strength over time, expressed in the particular measuring system adopted for the experiment. The signal itself appeared not to have changes that would have allowed for a message to be encoded, although any change that would have happened in less than 10 seconds or longer than 72 seconds would not have been detectable. The signal did, however, have a continuous wave.
The signal strength was measured by how much more powerful it was than the average background noise over the previous few minutes. The signal was sampled for 10 seconds and then processed by the computer, which took 2 seconds. Meaning that every 12 seconds the strength for each different frequency channel was printed on the printout as a single number or letter, representing the 10-second average strength, minus the strength of the background noise.
In this scale, an empty space was left for strengths between 0 and 1 standard deviations higher than the background noise. The numbers 1 to 9 showed how many standard deviations above the background noise the signal strength was. If the strength of the signal was 10 or above it would be indicated by a letter: "A" corresponded to a strength of 10, "B" to 11, "C" to 12, and so on. The Wow! signal's highest measured value was "U" (a strength of 30), making it thirty standard deviations above background noise.John Kraus, the director of the observatory, gave a value of in a 1994 summary written for Carl Sagan. However, Ehman in 1998 gave a value of . This is () above the hydrogen line value (with no red- or blue-shift) of . If due to blue-shift, it would mean the source was moving about towards Earth. An explanation of the difference between Ehman's value and Kraus's can be found in Ehman's paper.
The Wow! signal was a narrowband emission: meaning its bandwidth was less than kHz. The Big Ear telescope was able to measure fifty kHz-wide channels. The output from each channel was represented in the computer printout as a a different column with the number or letters printed on it representing the strength of the signal at that range. The Wow! signal is only in one column.
At the time the signal was heard, the Big Ear radio telescope was only adjustable for altitude (or height above the horizon), and used the spinning of the Earth to listen across the sky. Given how fast the Earth spins, and how big the telescope's observation window is, the Big Ear could listen to any given point in the sky for just 72 seconds. This means that a continuous extraterrestrial signal would only be able to be heard for exactly 72 seconds, and the recorded strength of such signal would display an increase for the first 36 seconds—peaking at the center of the observation window—and then a decrease as the telescope moved away from it. All these characteristics are present in the Wow! signal.
The exact spot in the sky where the signal came from is unclear because of the design of the Big Ear telescope. The telescope had two different structures (called feed horns) that listened to the sky, and both listened to the sky in slightly different directions, and would be moved along the sky by the Earth's spin. The Wow! signal was heard in one of these feed horns, but not in the other, and the data was processed in a way that makes it is impossible to determine which of the two horns heard the signal. Making two different spots in the sky where the signal could have come from.
The galactic coordinates for the positive horn are =11.7°, =−18.9°, and for the negative horn =11.9°, =−19.5°, both being therefore about 19° toward the southeast of the galactic plane, and about 24° or 25° east of the galactic centre. The region of the sky in question lies northwest of the globular cluster M55, in the constellation Sagittarius, roughly 2.5 degrees south of the fifth-magnitude star group Chi Sagittarii, and about 3.5 degrees south of the plane of the ecliptic. The closest easily visible star is Tau Sagittarii.
No nearby sun-like stars were within the are that was being listened to, although in any direction the antenna pattern would encompass about six stars that are far away.
There are a number of hypotheses as to what the Wow! signal is, and where it came from. Scientists have not gotten behind any one of these ideas. Interstellar twinkling of a weaker signal—similar in effect to twinkling of stars in the sky—could be an explanation, but that would not exclude the possibility of the signal being from extraterrestrials. The significantly more sensitive Very Large Array did not detect the signal, and the probability that a signal not detected by the Very Large Array could be detected by the Big Ear due to interstellar twinkling is low. Other hypotheses include a rotating lighthouse-like source, a signal sweeping in frequency, or just a one-time event.
Ehman has said: "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 took back his some of his doubt, after further research showed a signal coming from Earth to be very unlikely, given that whatever in space the signal would have bounced off of would have had to meet some unrealistic requirements. Also, other problems arise because the 1420 MHz signal is within a a bandwidth reserved for astronomical purposes, in which radios on Earth are banned from using. In a 1997 paper, Ehman suggest that not draw "vast conclusions from half-vast data"— and acknowledged the possibility that the signal may have been military or from people on Earth.