Wow! signal

Wow! signal

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The Wow! signal was a strong narrowband
In radio, narrowband describes a channel in which the bandwidth of the message does not significantly exceed the channel's coherence bandwidth. It is a common misconception that narrowband refers to a channel which occupies only a "small" amount of space on the radio spectrum.The opposite of...

Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...

 signal detected by Dr. Jerry R. Ehman
Jerry R. Ehman
Jerry R. Ehman is an American astronomer. He detected the strong narrowband radio signal known as Wow! signal on August 15, 1977 while working on a SETI project at the Big Ear radio telescope of Ohio State University.-Biography:...

 on August 15, 1977, while working on a SETI
The search for extraterrestrial intelligence is the collective name for a number of activities people undertake to search for intelligent extraterrestrial life. Some of the most well known projects are run by the SETI Institute. SETI projects use scientific methods to search for intelligent life...

 project at the Big Ear
The Big Ear
The Ohio State University Radio Observatory was a Kraus-type radio telescope located on the grounds of the Perkins Observatory at Ohio Wesleyan University from 1963 to 1998. Known as "Big Ear", the observatory was part of The Ohio State University's Search for Extraterrestrial Intelligence project...

 radio telescope
Radio telescope
A radio telescope is a form of directional radio antenna used in radio astronomy. The same types of antennas are also used in tracking and collecting data from satellites and space probes...

 of The Ohio State University then located at Ohio Wesleyan University's Perkins Observatory
Perkins Observatory
Perkins Observatory is an astronomical observatory in Delaware, Ohio. It is owned and operated by Ohio Wesleyan University.-Early history:The observatory is named for Hiram Perkins, a professor of mathematics and astronomy at the Ohio Wesleyan University in Delaware, Ohio from 1857 to 1907...

, Delaware, Ohio. The signal bore expected hallmarks of potential non-terrestrial
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 and non-solar system
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...

 origin. It lasted for the full 72-second
The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....

 duration that Big Ear observed 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
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...

 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
Alphanumeric is a combination of alphabetic and numeric characters, and is used to describe the collection of Latin letters and Arabic digits or a text constructed from this collection. There are either 36 or 62 alphanumeric characters. The alphanumeric character set consists of the numbers 0 to...

 code 6EQUJ5 describes the intensity
Intensity (physics)
In physics, intensity is a measure of the energy flux, averaged over the period of the wave. The word "intensity" here is not synonymous with "strength", "amplitude", or "level", as it sometimes is in colloquial speech...

- Physics :* Magnetic variation, difference between magnetic north and true north, measured as an angle* Variation , any perturbation of the mean motion or orbit of a planet or satellite, particularly of the moon- Mathematics :* Bounded variation...

 of the signal. A space
Space (punctuation)
In writing, a space is a blank area devoid of content, serving to separate words, letters, numbers, and punctuation. Conventions for interword and intersentence spaces vary among languages, and in some cases the spacing rules are quite complex....

 denotes an intensity between 0 and 1, the numbers 1 to 9 denote the correspondingly numbered intensities (from 1.000 to 10.000), and intensities of 10.0 and above are denoted by a letter ('A' corresponds to intensities between 10.0 and 11.0, 'B' to 11.0 to 12.0, etc.). The value 'U' (an intensity between 30.0 and 31.0) was the highest detected by the telescope, on a linear scale it was over 30 times louder than normal deep space. The intensity in this case is the unitless
Dimensionless quantity
In dimensional analysis, a dimensionless quantity or quantity of dimension one is a quantity without an associated physical dimension. It is thus a "pure" number, and as such always has a dimension of 1. Dimensionless quantities are widely used in mathematics, physics, engineering, economics, and...

 signal-to-noise ratio
Signal-to-noise ratio
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...

, where noise was averaged for that band over the previous few minutes.

Two different values for its frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...

 have been given: 1420.356 MHz (J. D. Kraus) and 1420.4556 MHz (J. R. Ehman). The frequency 1420 is significant for SETI searchers because, it is reasoned, hydrogen is the most common element in the universe, and hydrogen resonates at about 1420 MHz, thus extraterrestrials might use that frequency on which to transmit a strong signal. The frequency of the Wow! signal matches very closely with the hydrogen line
Hydrogen line
The hydrogen line, 21 centimeter line or HI line refers to the electromagnetic radiation spectral line that is created by a change in the energy state of neutral hydrogen atoms. This electromagnetic radiation is at the precise frequency of 1420.40575177 MHz, which is equivalent to the vacuum...

, which is at 1420.40575177 MHz. It is worth noting that the two different values given for the frequency of the Wow! signal (1420.356 MHz and 1420.4556 MHz) are the same distance apart to the hydrogen line - the first being about 0.0498 MHz less than the hydrogen line, and the second being about 0.0498 MHz more than the hydrogen line. The bandwidth of the signal is less than 10 kHz (each column on the printout corresponds to a 10 kHz-wide channel; the signal is only present in one column).

The original print out of the Wow! signal, complete with Jerry Ehman's famous exclamation, is preserved by the Ohio Historical Society
Ohio Historical Society
The Ohio Historical Society is a non-profit organization incorporated in 1885 as The Ohio State Archaeological and Historical Society "to promote a knowledge of archaeology and history, especially in Ohio"...


Location of the signal

Determining a precise location in the sky was complicated by the fact that the Big Ear telescope used two feed horn
Feed horn
In satellite dish and antenna design, a feedhorn is a small horn antenna used to convey radio waves between the transmitter and/or receiver and the reflector, particularly in parabolic antennas...

s 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, although the data was processed in such a way that it is impossible to determine in which of the two horns the signal entered. There are, therefore, two possible right ascension
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...

  • 19h22m24.64s ± 5s (positive horn)
  • 19h25m17.01s ± 5s (negative horn)

The declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...

 was unambiguously determined to be −27°03′ ± 20′. The preceding values are all expressed in terms of the B1950.0 equinox
Equinox (celestial coordinates)
-Overview:In astronomy, equinox is a moment in time at which the vernal point, celestial equator, and other such elements are taken to be used in the definition of a celestial coordinate system. The position at other equinoxes can be computed by taking into account precession, nutation and...


Converted into the J2000.0 equinox
Equinox (celestial coordinates)
-Overview:In astronomy, equinox is a moment in time at which the vernal point, celestial equator, and other such elements are taken to be used in the definition of a celestial coordinate system. The position at other equinoxes can be computed by taking into account precession, nutation and...

, the coordinates become RA= 19h25m31s ± 10s or 19h28m22s ± 10s and declination= −26°57′ ± 20′

This region of the sky lies in the constellation Sagittarius
Sagittarius (constellation)
Sagittarius is a constellation of the zodiac, the one containing the galactic center. Its name is Latin for the archer, and its symbol is , a stylized arrow. Sagittarius is commonly represented as a centaur drawing a bow...

, roughly 2.5 degrees south of the fifth-magnitude star group Chi Sagittarii
Chi Sagittarii
The Bayer designation Chi Sagittarii is shared by three star systems in the constellation Sagittarius. The brightest of these, χ¹ Sagittarii and χ³ Sagittarii, are separated by 0.56° on the sky. The dimmer χ² Sagittarii is located between them, 0.10° from χ¹...

. Tau Sagittarii
Tau Sagittarii
Tau Sagittarii is a star in the constellation Sagittarius, 120 light years from Earth. In ancient Chinese astronomy, it is the 5th star of 6 stars in the Dipper or 'South Dipper' mansion of the Black Tortoise of the North...

 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 peaking for the first 36 seconds—until 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 a possible extraterrestrial origin.

Searches for recurrence of the signal

The signal was expected to appear three minutes apart in each of the horns, but this 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 Gray searched for the event using the META array at Oak Ridge Observatory
Oak Ridge Observatory
The Oak Ridge Observatory, also known as the George R. Agassiz Station, is located at 42 Pinnacle Road, Harvard, Massachusetts, and was formerly operated by the Harvard-Smithsonian Center for Astrophysics as a facility of the Smithsonian Astrophysical Observatory .The observatory was established in...

, but did not re-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
H. Paul Shuch
Dr. H. Paul Shuch is an American scientist and engineer who has coordinated radio amateurs to help in the search for extraterrestrial intelligence.-Overview:...

 made several drift-scan observations of the 'Wow' signal's coordinates with a 12 meter radio telescope at the National Radio Astronomy Observatory
National Radio Astronomy Observatory
The National Radio Astronomy Observatory is a Federally Funded Research and Development Center of the United States National Science Foundation operated under cooperative agreement by Associated Universities, Inc for the purpose of radio astronomy...

, Green Bank WV, also achieving a null result.

In 1995 and 1996, Gray also searched for the signal using the Very Large Array
Very Large Array
The Very Large Array is a radio astronomy observatory located on the Plains of San Agustin, between the towns of Magdalena and Datil, some fifty miles west of Socorro, New Mexico, USA...

, which is significantly more sensitive than Big Ear.

Gray and Dr. Simon Ellingsen later searched for recurrences of the event in 1999 using the 26m radio telescope at the University of Tasmania
University of Tasmania
The University of Tasmania is a medium-sized public Australian university based in Tasmania, Australia. Officially founded on 1 January 1890, it was the fourth university to be established in nineteenth-century Australia...

's Mount Pleasant Radio Observatory
Mount Pleasant Radio Observatory
The Mount Pleasant Radio Observatory is a radio astronomy based observatory owned and operated by University of Tasmania, located 20 km east of Hobart. It is home to three radio astronomy antennas and the Grote Reber Museum.- Equipment :...

. Six 14-hour observations were made at positions in the vicinity, but did not detect anything similar to the Wow! signal.

Speculations on the signal's origin

Interstellar scintillation
Scintillation (astronomy)
Scintillation or twinkling are generic terms for rapid variations in apparent brightness or color of a distant luminous object viewed through a medium, most commonly the atmosphere ....

 of a weaker continuous signal
Continuous signal
A continuous signal or a continuous-time signal is a varying quantity whose domain, which is often time, is a continuum . That is, the function's domain is an uncountable set. The function itself need not be continuous...

—similar, in effect, to atmospheric twinkling
Scintillation (astronomy)
Scintillation or twinkling are generic terms for rapid variations in apparent brightness or color of a distant luminous object viewed through a medium, most commonly the atmosphere ....

—could be a possible explanation, although this still would not exclude the possibility of the signal being artificial in its nature. However, even by using the significantly more sensitive Very Large Array
Very Large Array
The Very Large Array is a radio astronomy observatory located on the Plains of San Agustin, between the towns of Magdalena and Datil, some fifty miles west of Socorro, New Mexico, USA...

, such a signal could not be detected, and the probability
Probability is ordinarily used to describe an attitude of mind towards some proposition of whose truth we arenot certain. The proposition of interest is usually of the form "Will a specific event occur?" The attitude of mind is of the form "How certain are we that the event will occur?" The...

 that a signal below the Very Large Array level could be detected by the Big Ear radio telescope due to interstellar scintillation is low. Other speculations include a rotating lighthouse-like source, a signal sweeping in frequency, or a one-time burst. Some have also suggested it could have come from a moving space vehicle of extraterrestrial origin.

Ehman has stated his doubts that the signal is of intelligent extraterrestrial
Extraterrestrial life
Extraterrestrial life is defined as life that does not originate from Earth...

 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
Space debris
Space debris, also known as orbital debris, space junk, and space waste, is the collection of objects in orbit around Earth that were created by humans but no longer serve any useful purpose. These objects consist of everything from spent rocket stages and defunct satellites to erosion, explosion...


He later recanted his skepticism somewhat, after further research showed an Earth-borne signal to be very unlikely, due to the requirements of a space-borne reflector being bound to certain unrealistic requirements to sufficiently explain the nature of the signal. Also, the 1420 MHz signal is problematic in itself in that it is "protected spectrum": it is bandwidth 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 in nature or otherwise may have been a production of Earth-bound humans.

See also

  • Arecibo message
    Arecibo message
    The Arecibo message was broadcast into space a single time via frequency modulated radio waves at a ceremony to mark the remodeling of the Arecibo radio telescope on 16 November 1974. It was aimed at the globular star cluster M13 some 25,000 light years away because M13 was a large and close...

  • Quasar
    A quasi-stellar radio source is a very energetic and distant active galactic nucleus. Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than...

    In astronomy, CTA 102, also known by its B1950 coordinates as 2230+114 and its J2000 coordinates as J2232+1143 , is a quasar discovered in the early 1960s by a radio survey carried out by the California Institute of Technology...

    , which was believed by Dr. Nikolai S. Kardashev to have an extraterrestrial signal encoded in it before further examination proved it to be a quasar, the first widely reported work of SETI activity.
  • Pulsar
    A pulsar is a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the lighthouse effect and gives rise to the pulsed nature that gives pulsars their name...

    Little green men 1 was the explanation given to a certain astronomical observation. In 1967, a radio signal was detected in a UK observatory by Jocelyn Bell and Antony Hewish. The signal had a 1.3373 second period and 0.04 second pulsewidth. It originated at celestial coordinates 19:19 right...

     ("Little Green Men 1"), the first pulsar signal to be recognised.
  • Radio source SHGb02+14a
    Radio source SHGb02+14a
    Radio source SHGb02+14a is a source and a candidate in the Search for Extra-Terrestrial Intelligence , discovered in March 2003 by SETI@home and announced in New Scientist on September 1, 2004....

External links