What Happened on August 15, 1977?
Late one summer night, astronomer Jerry Ehman was doing what he always did: reviewing reams of computer printout data from the Big Ear radio telescope at Ohio State University. The telescope was part of the SETI (Search for Extraterrestrial Intelligence) project, scanning the skies for radio signals that couldn't be explained by natural phenomena. As he scanned the columns of numbers and letters, a sequence from a few days prior caught his eye. It was an anomaly—a massive spike in signal strength from the direction of the constellation Sagittarius. The signal was so strong and so unusual that Ehman circled it in red pen and wrote a single word in the margin: 'Wow!'
Why Was This Signal So Special?
Radio telescopes pick up background noise from space all the time. What made the 'Wow!' signal different was its specific characteristics. It was a powerful, narrow-band signal, meaning it was transmitted on a very specific frequency, much like a terrestrial radio station. Natural cosmic sources, like pulsars or quasars, typically emit radiation across a broad range of frequencies. Furthermore, the signal was detected at a frequency of 1420 megahertz. This frequency, known as the 'hydrogen line,' is naturally emitted by hydrogen, the most common element in the universe. Scientists have long theorized that an intelligent civilization wanting to be found might use this fundamental frequency as a universal 'calling card.' The 'Wow!' signal fit the profile of a deliberate, artificial transmission almost perfectly.
Decoding the Infamous Printout: '6EQUJ5'
The strange sequence of characters '6EQUJ5' wasn't the message itself, but a representation of the signal's intensity over its 72-second duration. The computer measured the signal's strength every 12 seconds. Numbers 1-9 represented low intensities, and letters A-Z represented increasingly higher ones. A 'U' was 30 times stronger than the background noise of deep space. The signal peaked at 'U' and lasted for the full 72 seconds that the telescope was aimed at that specific patch of sky before Earth's rotation moved the telescope's view away. The signal's rise and fall over that period perfectly matched what you would expect from a fixed source in deep space being scanned by the telescope.
The Leading Theories
For over 45 years, scientists have debated the source of the signal, with two main camps of thought.
The E.T. Hypothesis
This is the most exciting possibility. The signal's characteristics—its narrow bandwidth, its frequency at the hydrogen line, and its immense power—all point toward an artificial origin. It could have been a powerful beacon or broadcast from a technologically advanced civilization, a message we just happened to overhear for a fleeting moment.
The Natural Phenomenon Hypothesis
Skeptics have proposed various natural explanations, though none have been entirely convincing. One theory suggested the signal came from a hydrogen cloud surrounding two comets, but this was later largely debunked as the comets were not in the right position at the time. Other possibilities include a rare type of pulsar or some other, as-yet-unknown astronomical event. However, no known natural source fully explains all the features of the signal.
Why We've Never Heard It Again
This is the most frustrating part of the mystery. Despite hundreds of subsequent searches of the same region of the sky, the signal has never been detected again. If it was an alien beacon, why was it turned off? Was it a one-time message? Or was it a transmission from a moving source, like a spacecraft, that has since traveled out of range? The silence that followed the 'Wow!' signal is as puzzling as the signal itself, leaving it as a singular, tantalizing 'what if' in the history of science.
Frequently Asked Questions
Where did the Wow! signal come from?
The signal originated from the direction of the constellation Sagittarius, near a star cluster called M55. However, there are no obvious sun-like stars in the precise area the telescope was pointing.
Could it have been a signal from Earth?
This is highly unlikely. The 1420 MHz frequency is protected for astronomical use, meaning terrestrial transmissions are forbidden. Furthermore, the signal's profile perfectly matched a source moving with the rotation of the sky, not a fixed source on or near Earth.
Is it the only unexplained signal we've ever found?
Astronomers have detected other strange signals, like Fast Radio Bursts (FRBs), but most have different characteristics. The 'Wow!' signal remains unique in how closely it matched the profile of a potential E.T. broadcast.
Summary: Key Takeaways
- The 'Wow!' signal was a powerful, 72-second radio signal detected from deep space in 1977.
- Its characteristics closely matched what scientists would expect from an artificial, extraterrestrial source.
- It was nicknamed for the surprised note written by the astronomer who discovered it.
- Despite numerous attempts, the signal has never been detected again.
- Its origin remains one of the greatest unsolved mysteries in modern astronomy.