Short take:
Famous signal received on 11:16 p.m.EDT August 15, 1977 by the Big Ear radio telescope as part of the SETI program, and considered the closest "near miss" in SETI history. After 20 years, no confirmation or explanation for this signal has been found, making it more or less completely inconclusive as evidence for an artificial signal.

Longer explanation:
Poring over computer printouts, Dr. Jerry R. Ehman noticed the string 6EQUJ5 in the second channel. He circled this pattern and wrote the word "Wow!" that has since been so ubiquitous in SETI literature. Each character represented the average strength of the radio signal over a 12-second period. Thus the entire Wow! signal is basically a single, low-resolution, 72-second narrow-band burst of radio waves emerging from somewhere in the Sagittarius region of the sky. (The actual time resolution of the telescope was ten times greater, but this was averaged to save printout space.) The whole of extant Wow!, by Dr. Ehman's admission, is six data points. While the signal's source has not been pinpointed, that area of the sky was subsequently searched in detail to no avail.

There are two possibilities--the null hypothesis is that it is a fluke of one kind or another, and the alternative being that it was an artificial, extraterrestial signal that for some reason abruptly stopped transmitting or changed direction. With only six questionable data points to work with, there is no choice but to tentatively accept the null hypothesis. Extraordinary claims demand extraordinary evidence.

August 15, 1977 - Ohio State University at the radio telescope the "Big Ear". This was one of the early observatories in the search for extra terrestrial intelligence - before SETI was founded (1984). The Big Ear scanned the heavens and clattered away on a printer printing out some text. The text printed out was for each channel that was being observed - 50 channels total. On channel 2 the string read "6EQUJ5" which astonished Jerry Ehman (who was working that night) and he grabbed a pen, and circled that string and wrote "Wow!". Looking back, Ehman says "I mean, without thinking, I wrote 'Wow!' It was the most significant thing we had seen."

The string "6EQUJ5" refers to the characteristics of the signal. Each character represents an intensity on a scale from 1 to 35 (it went higher, looping over again so that a 38 would be represented as a '3'). Each letter represents 10 seconds of observation (and another 2 seconds of computation) Over 37 seconds (an important number that shall be returned to) the signal went from 0 to 30 sigmas above the background nose up to a strength of 'U' and then faded again back to 0 (background noise) over another 37 seconds.

  • 6 ->  6.0 -  6.9 sigmas above background
  • E -> 14.0 - 14.9 sigmas above background
  • Q -> 26.0 - 26.9 sigmas above background
  • U -> 30.0 - 30.9 sigmas above background
  • J -> 19.0 - 19.9 sigmas above background
  • 5 ->  5.0 -  5.9 sigmas above background
The value 'U' was the strongest signal ever seen on the Big Ear.

The duration that was observed was the exact duration that the Big Ear watched a particular spot in the sky as the earth moved. Secondly, the bell shape of the intensity is what one would see watching a distant point (rather than in earth orbit - which would also have a different time) as it the antenna moved into the path of the signal and moved out. This rules out Earth and near Earth radio interference.

Another point to consider is that this signal was not always on. The Big Ear had two separate scans of the same spot in the sky separated 3 minutes. The 'Wow' signal only showed up on one of them and apparently was 'turned off' by the time the second scan looked at that part of the sky.

For some time after the Wow signal, attempts were made to find it again. No search has found that signal. In 1987 and 1989 an 84 foot radio telescope was used to look at possible spots in the sky but found nothing. Most recently, the VLA was used in 1995 and 1996 to investigate some possibilities including a weak signal that grew in strength due to various lensing http://www.bigear.org/Gray-Marvel.pdf . If this was the case, the VLA would have found it - but the VLA did not find any that sources resembling the Wow signal. A second possibility was that the Wow signal was a "look here!" followed by a lower power signal. The VLA is capable of detecting signals 1000x weaker than the Big Ear could, but found nothing. Another still possible situation is that the Wow signal isn't on all the time (the Arecibo transmission isn't on all the time either - it was sent just once on November 16, 1974 ). Time on the VLA and other large telescopes is often limited to just an hour or two and the locale for the signal is below the horizon in the northern hemisphere most of the day. A search that lasted fourteen hours and composed of several telescopes across the world also found no periodic signal during that period http://www.bigear.org/Gray-Ellingsen.pdf (though it is noted that the period of the signal may be/have been longer than 14 hours).

While this was a clearly artificial signal, the question remains what was it. No planets were in that part of the sky - this wasn't something from Jupiter. None of the known large asteroids were in that part of the sky to bounce a signal back. The frequency of 1420 MHz is off limits for commercial and military use being reserved for scientific observation. No known satellites were in the path of the radio telescope at that time. Aircraft move with respect to the celestial background and the duration wouldn't be what it was. While unlikely, it could have been a bit of earth originated RFI that just happened to look like something from space (this is one of the possibilities mentioned in the review) - though it is still the case that nothing should be transmitting at 1420 MHz. It is possible that this was a harmonic of a transmission at 710 MHz (for example), however there are filters in place and the signals at 710 MHz are typically much broader than the 10 KHz range that was used for each channel on the Big Ear and would have shown up in multiple channels.

Thus, since all of the possibilities of a terrestrial origin have been either ruled out or seem improbable, and since the possibility of an extraterrestrial origin has not been able to be ruled out, I must conclude that an ETI (ExtraTerrestrial Intelligence) might have sent the signal that we received as the Wow! source. Of course, being a scientist, I await the reception of additional signals like the Wow! source that are able to be received and analyzed by many observatories. Thus, I must state that the origin of the Wow! signal is still an open question for me. There is simply too little data to draw many conclusions. In other words, as I stated above, I choose not to "draw vast conclusions from 'half-vast' data".

Dr. Jerry R. Ehman - 20 years after - http://www.bigear.org/wow20th.htm
http://planetary.org/html/news/articlearchive/headlines/2001/Wow.htm
http://www.bigear.org/wowmenu.htm

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