Thirty years ago today, a volunteer at the Big Ear Radio
Observatory at Ohio State University (OSU) monitored a strong signal from outer
space. Was this Earth's first encounter with intelligent, extraterrestrial
life? Jerry Ehman, the OSU volunteer who scrawled "Wow!" on the original computer
printout, was ecstatic about that very possibility. "I mean, without thinking,
I wrote 'Wow!'", Ehman later recalled. "It was the most significant thing
we had seen."
The "Wow! Signal" that Ehman detected on August 15, 1977 captured
the imaginations of astronomers around the world. Students of the night skies
aimed their telescopes at the point where the signal seemed to originate, but were greeted with silence. Their failure to find anything made many people,
including Ehman, skeptical. "Even if it were intelligent beings sending a
signal, they'd do it far more than once," the astronomer later told the
Cleveland Plain Dealer. "We should have seen it again when we looked for it 50
times. Something suggests it was an Earth-bound signal that simply got reflected off a piece of space debris."
What About the Code on the Printout?
The photo at the top-left depicts the computer printout with Jerry Ehman's handwrittten comment ("Wow!") and six circled characters (6EQUJ5) that are aligned vertically. So what does this code mean?
Each of the first 50 columns indicates the
successive values of intensity (or power) received from the Big Ear
radio telescope in each channel (10 kHz wide) in successive 12-second
intervals. Ten seconds were used for sampling and another two seconds were used for computer processing.
To conserve space on the printout, Ehman used a
coding method of one alphanumeric character for each intensity. The
observatory's computer was programmed to
keep a continuously-updated account for each channel of a baseline
value and a root mean square (RMS) value.
After the baseline value was subtracted, the actual intensity was divided by the RMS value to obtain a scaled value. Because there was room for
only one character on the printout, Ehman used only the integer value of this scaled intensity for values ranging from 0 to 9.999.
The value of zero printed as a blank
(space). Value of 1, 2, 3, 4, 5, 6, 7, 8, and 9 were
printed directly. For scaled intensities from 10 to 35, capital letters were used. For example, a truncated value of
10 printed as an "A" while a truncated value of 11 printed as a "B". When the scaled intensity exceeded 36, the program would start over again
at zero. So, a truncated value of 38 printed as that of 38 - 35 = 3 (i.e., 3).
The 6EQUJ5 code in channel 2 indicates successive intensities as
follows:
6 = 6.0 - 6.999
E = 14.0 - 14.999
Q = 26.0 - 26.999
U = 30.0 - 30.999
J = 19.0 - 19.999
5 = 5.0 - 5.999
The value "U" (a range of 30.0 - 30.999) was the largest value that Ehman and another volunteer, Bob Dixon, had ever seen. Because the intensity never exceeded
31.0, there was no rollover. "It
would have been easy to spot in a sequence of 6 or 7 numbers," Ehman explained, "that
should follow the antenna pattern of the telescope."
Although the six successive values in channel 2 fit the antenna pattern of Big Ear, Jerry Ehman also completed a correlation analysis of the six data points with the mathematical functions: (1) gaussian = normal curve; and
(2)(sin(x)/x)^2. Again, the data fit each of those two functions,
with correlation coefficients of over 0.99.
In addition, Ehman fit the data to each of the two actual antenna patterns of the two horns, using the moderately strong radio source OY372.
Again, the correlation coefficients were over 0.99. Unfortunately, there was not
enough difference between the two correlation coefficients to
determine which horn the "Wow! signal" was received in.
Resources:
http://www.wired.com/science/discoveries/news/2007/08/dayintech_0815
http://www.bigear.org/wow.htm
http://www.bigear.org/6equj5.htm
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