On Aug. 15, 1977, a 72-second radio signal from space stirred up the Search for Extra-Terrestrial Intelligence (SETI). Astronomer Jerry Ehman viewed the signal on a computer printout and wrote the word “Wow!” on the sheet, giving the signal the moniker it has today. The signal came from the Sagittarius constellation near the center of the galaxy.
Ehman recalled in an interview with Cleveland’s The Plain Dealer: “It was the most significant thing we had seen.”
The signal, which appeared as the six characters 6EQUJ5, did not have any apparent meaning. It was received by Ohio State University’s Big Ear radio observatory. It caused much excitement, but a similar transmission has not been discovered since, leading many to lose hope that it was an attempt by extraterrestrials to make contact. But it remains a mystery 37 years later, leaving the tantalizing uncertainty—a thread to draw the imagination up into space and onto other worlds inhabited by intelligent life.
The Wow! signal showed a spike in the normal radio waves received from outer space and lasted 72 seconds, which was extremely unusual. (Wikimedia Commons)
The Big Ear was used, starting in 1965, to survey celestial radio sources. Objects in the cosmos, such as pulsars, quasars, and certain nebulas, emit large amounts of radio waves. In the 1970s, it’s focus shifted and it became the first device to constantly survey radio waves from space in search of extraterrestrial communication. Though radio waves are emitted by many objects in space, the Wow! signal was very unusual—in exactly the ways we’d expect a message from aliens to be unusual.
It was resonating at 1420 MHz, on the hydrogen line. “Hydrogen line” refers to a frequency that is said to be the most likely for communication from intelligent extraterrestrial life. In 1959 Philip Morrison at Cornell University and Frank Drake at the National Radio Astronomy Observatory independently recognized this likelihood, explains the SETI website.
“They reasoned that more advanced civilizations would reason that young civilizations (like ours) might already be listening there,” according to SETI.
The hydrogen line is named as such because it is the frequency of the waves emitted by neutral hydrogen atoms. The International Telecommunications Union protects this frequency to avoid “noise” on it from earthly sources. Astronomers have used it in their studies for such purposes as making maps based on emissions from hydrogen atoms in space.
The Wow! signal’s strength and shifts in intensity along the hydrogen line make it a likely candidate for extraterrestrial communication.
Brian Dunning said on Skeptoid: “If we ever do receive a deliberate alien transmission, Wow! was exactly what we’d hope and expect to find.”