Discovery
The Discovery
The Big Ear radio telescope was a dedicated SETI (Search for Extraterrestrial Intelligence) instrument operated by The Ohio State University from 1973 to 1995.
In 1977, observational data were printed on continuous computer paper by a typewriter-style printer. About three or four days after each observation, the printouts were delivered to the home of radio astronomer Dr. Jerry R. Ehman.
On August 15, 1977, Dr. Ehman spread the latest printout across his kitchen table and began examining the data. He was astonished to discover an unusually strong and highly anomalous radio signal. He circled the remarkable sequence with a red pen and wrote the word “Wow!” in the margin.
This moment marked the discovery of what is now known as the Wow! Signal, one of the greatest mysteries in the history of SETI.
Characteristics
Signal Characteristics
The signal had the following characteristics:
- Its source was located in one of two very closely spaced regions in the constellation Sagittarius. Because of the observing configuration of the Big Ear telescope, it has never been determined which of the two positions was the true source.
- The signal lasted somewhere between 72 seconds and approximately 2.5 minutes. Again, the exact duration cannot be determined because of the observing method used by Big Ear.
- Its intensity was about 30 times stronger than the background noise (corresponding to approximately 54 Jy or 212 Jy, depending on the assumed source position).
- Its frequency was 1420 MHz (the 21 cm hydrogen line).
- No known astronomical body—including the Moon, any planet, or the two interplanetary spacecraft then in operation (Pioneer 10 and Pioneer 11)—was located in the direction from which the signal appeared to originate.
Mystery
Why Is It Still a Mystery?
Several features make the Wow! Signal particularly intriguing:
- 1420 MHz has long been regarded as one of the most likely frequencies that an extraterrestrial civilization might choose for interstellar communication, as first proposed by Cocconi & Morrison (1959).
- Transmissions by humans at 1420 MHz are prohibited by the International Telecommunication Union (ITU) in order to protect radio astronomy observations.
- The signal’s bandwidth was less than 10 kHz, making it difficult to explain as a natural astrophysical radio source.
- The source exhibited the apparent sidereal motion expected of a celestial object, indicating that it was not transmitted from a terrestrial source, an aircraft, or an artificial satellite.
Aftermath
Follow-up Observations
Following the original detection, numerous follow-up observations were carried out, both with Big Ear and at other observatories around the world. However, no signal with similar characteristics has ever been detected again.
The origin of the Wow! Signal continues to be debated in leading astronomical journals, and despite decades of investigation, its true nature remains unknown. Because the signal was detected only once, the available observational evidence is extremely limited, making it extraordinarily difficult to identify its source.