Wow!-Signal

The Wow! Signal was a narrow- band radio signal on 15 August 1977 was scribbling astrophysicist Jerry R. Ehman as part of a SETI project at the "Big Ear" radio telescope at Ohio State University from the direction of the constellation Sagittarius. The cause of the signal is not clearly understood.

The signal

Frequency and strength

The signal was significantly greater than the background noise of 30 times the standard deviation. The bandwidth is less than 10 kHz. Two different values ​​of its frequency are specified, 1420.356 MHz ( JD Kraus, old value) and 1420.456 MHz ( JR Ehman, revised value ), but both very close to the frequency of 1420.405 MHz, generated by the hyperfine transition of neutral hydrogen in the universe. The difference between these two values ​​can be explained by an error in the system, which was discovered and corrected until after the signal. Also two possible equatorial coordinates were given: RA = 19h22m22s ± 5s or 19h25m12s ± 5s, as well as both Dec. = -27 ° 03 '± 20' ( in the epoch B1950.0 ). This region lies in the constellation Sagittarius, about 2.5 degrees south of the group Chi Sagittarii. Tau Sagittarii is the closest visible star. The signal was thus at least 122 years old when it hit the antenna.

Puzzled as narrow-band signal was and how much the intensity profile of the possible, which would produce a localized signal in the antenna used, Ehman R. J. bordered on the computer printout of the character code " 6EQUJ5 " ( the received intensities were ascending coded with the numbers 1 to 9, with 9 out with the letters A to Z, "Z " → highest intensity ) of the intensity variation with the pen and wrote the comment "Wow!" ( Donnerwetter! ) to the edge. This comment became the name of the signal.

Since the "Big Ear" radio telescope was fixed on the sky and therefore moved along with the Earth's rotation, it can be assumed that an interstellar signal as opposed to a terrestrial or solar system bound signal would be doing first increased in intensity after 36 seconds its would have reached climax and then slowed again. Since the signal corresponded exactly to this template, the probability that there is indeed an interstellar signal, extremely high. But then another reception window was exactly tracked three minutes after that first window and the signal would have a corresponding three minutes afterwards must also receive; However, this was not the case.

It has been speculated whether interstellar oscillation of a weaker continuous signal (an effect similar to the atmospheric twinkling of stars ), a possible explanation (although this would not refute an artificial origin of the signal ). However, the signal with the much more sensitive Very Large Array could also not be detected. The probability that a signal below the sensitivity of the Very Large Array of the " Big Ear " radio telescope due to interstellar scintillation is received, is extremely low, at less than 10-40.

It is unlikely, however, possible that the signal is of terrestrial origin or derived from an object within the solar system. The signal was measured 72 seconds long and apparently did not repeat itself; all subsequent investigations - by Ehman itself and others - could not locate it. Therefore, the nature of the signal remains unclear and so far some opportunities may only be excluded.

Interpretation of paper - expression

The coding is derived from the program used for evaluation, and provides the received signal strength as a sign dar. Ehman describes in detail:

The selected characters 6EQUJ5 in Figure 1 describe the course of the strength of the signal.

• Free space means strength between 0 and 1
• Numbers 1 to 9 mean signal strength levels, similar to how they are used in professional radio, amateur radio and CB radio. The (voltage) values ​​are between 1,000 and 10,000.
• Higher values ​​10 and higher get letters.
• "A" means strength 10 to 11
• "B" means strength 11-12 etc. up to Z

"U", thickness between 30 and 31 was the largest received. On a logarithmic scale it was about 30 times stronger than normal noise in space. The strength of the signal to noise ratio wherein the noise is measured as the average of the preceding minutes in this case.

Change with time

Figure 2 shows the character as a curve, so the course of the reception strength over time. The real strength of the signal could have been constant through the fixed mounting of the antenna and by the rotation of the earth the receiving lobe was rotated past the signal. So had a change of very weak over strong result to very weak, similar to a bell curve.

" Horizontal " Information

The above statement is concerned with the vertical columns in Figure 1, especially with the column with the code sequence of the signal strengths.

Horizontal from left to right, are next to each other 20 columns in Figure 1. These represent 20 channels in which the same received signals.

The bandwidth of each channel was 10 kHz. Figure 1 can be found in the rest of the channels no strong signals, only the general weak noise.

Modulation, content possible?

Jerry Ehman discussed in his essay The Big Ear Wow! Signal detail details. In a chapter of the document he discusses the question of whether it is possible that the signal modulation, ie content contained.

The answer of Dr. Ehman is: ' Yes, this is possible. ' But at the time the receiver was not powerful enough. The then computer was not. Thus at this stage of the art you would already be able to use a much more narrowband receiver, namely with a bandwidth of 0.5 kHz, and a second computer for analysis. If the signal contained a modulation about a similar as we used in our Arecibo message, we could not determine the content due to our simple, broad-band receiver.

Possible explanations

As part of the television documentary The Aliens - Myth and Truth ( ZDF, 2010) Harald Lesch explained that the Wow signal! All the hallmarks of an interstellar communication experiment showed it could be but also have been a gigantic eruption of the pulsar.

Big Ear radio telescope

The Ohio State University Radio Observatory, only short The Big Ear ( German: The big ear) called, was a radio telescope in the grounds of Ohio Wesleyan University and was until 1995 part of a SETI search program at Ohio State University. On the Big Ear longest SETI search program was conducted from 1973 to 1995. After nearly 40 years of operation, the telescope was dismantled in 1998, sold the site and then used as a golf course.