The Wow! signal was a strong narrowband radio signal detected by Jerry R. Ehman on August
15, 1977, while he was working on a SETI project at the Big Ear radio telescope of The Ohio
State University, then located at Ohio Wesleyan University's Perkins Observatory in Delaware,
Ohio. The signal bore the expected hallmarks of non-terrestrial and non-Solar System origin.
It lasted for the full 72-second window that Big Ear was able to observe it, but has not
been detected again. The signal has been the subject of significant media attention.
Amazed at how closely the signal matched the expected signature of an interstellar signal
in the antenna used, Ehman circled the signal on the computer printout and wrote the comment
"Wow!" on its side. This comment became the name of the signal.
Interpretation of the paper chart The circled alphanumeric code 6EQUJ5 describes
the intensity variation of the signal. A space denotes an intensity between 0 and 1, the
numbers 1 to 9 denote the correspondingly numbered intensities, and intensities of 10.0
and above are denoted by a letter. The value 'U' was the highest detected by the radio
telescope; on a linear scale it was over 30 times louder than normal deep space. The intensity
in this case is the unitless signal-to-noise ratio, where noise was averaged for that band
over the previous few minutes. Two different values for its frequency have
been given: 1420.356 MHz and 1420.4556 MHz. The frequency of the Wow! signal matches very
closely with the hydrogen line, which is at 1420.40575177 MHz. The hydrogen line frequency
is significant for SETI searchers because, it is reasoned, hydrogen is the most common
element in the universe, and hydrogen resonates at about 1420.40575177 MHz, so extraterrestrials
might use that frequency to transmit a strong signal. The two different values given for
the frequency of the Wow! signal are the same distance apart from the hydrogen line—the
first being about 0.0498 MHz less than the hydrogen line, and the second about 0.0498 MHz
more. The bandwidth of the signal is less than 10 kHz.
The original printout of the Wow! signal, complete with Jerry Ehman's famous exclamation,
is preserved by the Ohio Historical Society. Location of the signal
Determining a precise location in the sky was complicated by the Big Ear telescope's
use of two feed horns to search for signals, each pointing to a slightly different direction
in the sky following Earth's rotation; the Wow! signal was detected in one of the horns
but not in the other, and the data was processed in such a way that it is impossible to determine
which of the two horns the signal entered. There are, therefore, two possible right ascension
values: 19h22m24.64s ± 5s
19h25m17.01s ± 5s The declination was unambiguously determined
to be −27°03′ ± 20′. The preceding values are all expressed in terms of the B1950.0
equinox. Converted into the J2000.0 equinox, the coordinates
become RA= 19h25m31s ± 10s or 19h28m22s ± 10s and the declination becomes −26°57′ ± 20′.
This region of the sky lies 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. Tau Sagittarii is the closest easily visible star.
Time variation
The Big Ear telescope was fixed and used the rotation of the Earth to scan the sky. At
the speed of the Earth's rotation, and given the width of the Big Ear'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 that signal would show a gradual increase for the first 36 seconds—peaking when the
signal reached the center of Big Ear's observation "window"— and then a gradual decrease.
Therefore, both the length of the Wow! signal, 72 seconds, and the shape of the intensity
graph may correspond to an extraterrestrial origin.
Searches for recurrence of the signal The signal was expected to appear three minutes
apart in each of the horns, but that did not happen. Ehman unsuccessfully looked for recurrences
of the signal using Big Ear in the months after the detection.
In 1987 and 1989, Robert H. Gray searched for the event using the META array at Oak
Ridge Observatory, but did not detect it. In a July 1995 test of signal detection software
to be used in its upcoming Project Argus search, SETI League executive director H. Paul Shuch
made several drift-scan observations of the Wow! signal's coordinates with a 12-meter
radio telescope at the National Radio Astronomy Observatory in Green Bank, West Virginia,
also achieving a null result. In 1995 and 1996, Gray also searched for the
signal using the Very Large Array, which is significantly more sensitive than Big Ear.
Gray and Simon Ellingsen later searched for recurrences of the event in 1999 using the
26m radio telescope at the University of Tasmania's Mount Pleasant Radio Observatory. Six 14-hour
observations were made at positions in the vicinity, but nothing like the Wow! signal
was detected. Speculation on the signal's origin
Interstellar scintillation of a weaker continuous signal—similar in effect to atmospheric
twinkling—could be an explanation, but that would not exclude the possibility of the signal
being artificial in origin. But even the significantly more sensitive Very Large Array could not
detect the signal, and the probability that a signal below the Very Large Array level
could be detected by the Big Ear due to interstellar scintillation is low. Other speculations include
a rotating lighthouse-like source, a signal sweeping in frequency, or a one-time burst.
Ehman has voiced doubts that the signal was of intelligent extraterrestrial origin: "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 recanted
his skepticism somewhat, after further research showed an Earth-borne signal to be very unlikely,
given the requirements of a space-borne reflector being bound to certain unrealistic requirements
to sufficiently explain the signal. Also, the 1420 MHz signal is problematic in itself
in that it is "protected spectrum": bandwidth reserved for astronomical purposes in which
terrestrial transmitters are forbidden to transmit. In his most recent writings, Ehman
resists "drawing vast conclusions from half-vast data"—acknowledging the possibility that
the source may have been military or otherwise a product of Earth-bound humans.
Scientists say that if the signal came from extraterrestrials, they are likely to be an
extremely advanced civilization, as the signal would have required a 2.2-gigawatt transmitter,
vastly more powerful than any on Earth: the Earth transmitters with the highest power
are the Taldom transmitter at 2500 kW in long wave and the Bolshakovo transmitter at 2500 kW
in medium wave. Response
In 2012, on the 35th anniversary of the Wow! signal, Arecibo Observatory beamed a response
from humanity, containing 10,000 Twitter messages, in the direction from which the signal originated.
In the response, Arecibo scientists have attempted to increase the chances of intelligent life
receiving and decoding the celebrity videos and crowd-sourced tweets by attaching a repeating
sequence header to each message that will let the recipient know that the messages are
intentional and from another intelligent life form.
See also
Arecibo message Lone Signal
Pulsar PSR B1919+21(LGM-1), the first pulsar signal to be recognised.
Quasar CTA-102, which was believed by Dr. Nikolai S. Kardashev to have an extraterrestrial
signal encoded in it before further examination showed it to be a quasar, the first widely
reported work of SETI activity. Radio source SHGb02+14a
References
External links Location on Google Sky
Location on YourSky APOD NASA GOV NASA Signal 2011
Dunning, Brian. "Was the Wow! Signal Alien?". Skeptoid.com. Retrieved 2013-07-01.
Ehman, Jerry R.. "The Big Ear Wow! Signal". North American AstroPhysical Observatory.
Retrieved 2013-07-01.