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| The Wow! signal celestial location |
Today it's the 40th anniversary of the Wow! signal. Joseph de Ca'th Lon wants to talk us about it.
Astronomer Jerry R. Ehman discovered the anomaly a few days later while reviewing the recorded data. He was so impressed by the result that he circled the reading on the computer printout and wrote the comment Wow! on its side, leading to the event's widely used name.
More information: WOW Signal recieved at SETI on August, 15 1977
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 several subsequent attempts by Ehman and others. Many hypotheses have been advanced on the origin of the emission, including natural and man-made sources, but none of them adequately explains the result. The Wow! signal remains therefore the strongest candidate for an alien radio transmission ever detected.
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| Astronomer Jerry R. Ehman |
In 1973, after completing an extensive survey of extragalactic radio sources, Ohio State University assigned the now-defunct Big Ear telescope, then located near the Perkins Observatory in Delaware, Ohio, to the scientific Search for ExtraTerrestrial Intelligence (SETI), in the longest-running program of its kind in history.
Over a decade earlier, in a 1959 paper, Cornell 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, which is naturally emitted by hydrogen, the most common element in the universe and therefore likely familiar to all technologically advanced civilizations.
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 minicomputer and printed on perforated 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.
More information: Ohio History Central
The alphanumeric sequence circled by Ehman, 6EQUJ5, represents the intensity variation of the radio signal over time, measured as unitless signal-to-noise ratio and ranging from 0 to 36, with the noise averaged over the previous few minutes. Each individual character corresponds to a sample of the signal, taken every 12 seconds. A space character on the printout denotes an intensity between 0 and 1; the numbers 1 to 9 denote the correspondingly numbered intensities -from 1 to 9-; intensities of 10 and above are indicated by a letter: A corresponds to intensities between 10 and 11, B to 11 to 12, and so on. The highest measured value was U -an intensity between 30 and 31-, that is thirty times stronger than normal background noise.
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| Sky on August 15, 1977 |
A common misconception is that the Wow! signal constitutes some sort of message.
In fact, what was received appears to be an unmodulated, continuous wave signal with no encoded information; essentially a flash of radio energy.
The string 6EQUJ5 is merely the representation of the expected variation of signal intensity over time, expressed in the particular measuring system adopted for the experiment.
In fact, what was received appears to be an unmodulated, continuous wave signal with no encoded information; essentially a flash of radio energy.
The string 6EQUJ5 is merely the representation of the expected variation of signal intensity over time, expressed in the particular measuring system adopted for the experiment.
At the time of the observation, the Big Ear radio telescope was only adjustable for declination -or height above the horizon-, and relied instead on the rotation of the Earth to scan across the sky. Given the speed of Earth's rotation and the spatial width of the telescope's observation window, the Big Ear could observe any given point for just 72 seconds. A continuous extraterrestrial signal, therefore, would be expected to register for exactly 72 seconds, and the recorded intensity of such signal would display a gradual increase for the first 36 seconds -peaking at the center of the observation window- and then a gradual decrease. All these characteristics are present in the Wow! signal.
More information: Phys
The Wow! signal was a narrowband emission: its bandwidth was less than 10 kHz. The Big Ear telescope was equipped with a receiver capable of measuring fifty 10 kHz-wide channels. The output from each channel was represented in the computer printout as a column of alphanumeric intensity values. The Wow! signal is essentially confined to one column.
A person not familiar with all of the special knowledge about a particular instrument should not try to draw too many conclusions from printed data. Such data typically contains certain assumptions about the equipment not necessarily known to outsiders.
Jerry R. Ehman
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