What Was The Wow! Signal And Why Is It So Famous? (2024)

When astronomer Jerry Ehman noticed something unusual in the printout from Ohio State University’s radio telescope, his response became the most famous moment in the search for extraterrestrial intelligence. In recent years several explanations for what became known as the "Wow! signal” have been published. However, since these contradict each other, it is fair to say the question is unsettled.

The Wow! Signal In Context

From the invention of the radio telescope in 1932 some people hoped we might capture alien signals, but almost all the telescopes’ times were devoted to exploring the most intriguing natural objects.

The Search for Extra Terrestrial Intelligence (SETI) started seeking radio signals from aliens in 1960, but initial efforts were brief and haphazard. The instruments at the time were not only limited to small areas of the sky, but narrow parts of the radio band. The frequency 1420 MHz was thought to be a likely one on which aliens might operate if they were trying to attract attention, as it is one of those naturally emitted by hydrogen. So when Ohio State University allocated its dish, nicknamed “Big Ear” to the hunt, bands around this frequency were chosen.

Compared to modern radio telescopes Big Ear could only collect tiny amounts of data, and prior to the Wow! signal nothing had picked up nothing remotely as interesting.

It’s also important to understand, before getting to the detection itself, that the word “signal” can create a lot of confusion in this context. To many non-scientists “signal” sounds deliberate, implying a message, whether alien or human. However, to a scientist, a signal is anything that is not random noise – radio emissions from a neutron star or even Jupiter represent definite signals, but are certainly natural.

Big Ear was not suited to moving around the sky to chase specific targets. Instead, it pointed at a particular spot relative to Earth and let the planet’s rotation adjust. Allowing for the width of the sky Big Ear could capture, each spot was recorded for 72 seconds. If there had been an alien civilization trying to attract our attention from a distant location, Big Ear would have detected an increasingly powerful signal for 36 seconds, followed by a gradual decline to silence.

Of course, there could be plenty of natural sources that would produce something similar.

What Was Special About the Wow! Signal?

When Big Ear was operating, anything the telescope detected was printed out on line paper. Volunteer Jerry Ehman noticed a signal lasting 72 seconds collected on August 15, 1977 and represented as 6EQUJ5. Ehman circled these characters and wrote “Wow!” next to them in red pen.

Some people have misunderstood the signal as Big Ear receiving those letters from space, which would warrant more than a “wow”, but this is not correct. Instead, the symbols referred to the ratio between the signal strength in a 10 second period and the baseline noise averaged over the previous few minutes. Anything equal or lower than the baseline was represented by a blank space. Intensity up to nine times the background was indicated with numbers, while higher intensities were represented in letters.

Consequently, the characters Ehman circled meant 10 seconds of 6-7 times background, followed by 10 seconds at 14-15 times background. The presence of the U indicates that at peak the telescope was picking up something at 30-31 times stronger than the background, but tells us nothing at all about what it is.

One of the expected features of alien signals is that they will be quite narrowband. Broadcasting over a lot of frequencies wastes energy, and if you want to communicate it makes sense to keep things tight and clear.

Big Ear only had a resolution of 10 kHz (modern SETI telescopes have resolution thousands of times tighter), so while we know the Wow! signal was not wider than that, we can’t tell how much narrower it was. Ten kHz is narrower than the bulk of astronomical signals, but it’s not unknown for natural sources to be this narrowband.

The frequency at which the signal was detected was slightly higher than the hydrogen line. This could indicate the source was something other than hydrogen, or that it was a hydrogen emission blue-shifted by travelling towards Earth at about 10 kilometers per second (22,000 mph) Although fast in earthy terms, this is slower than incoming meteors, for example.

What Explanations Have Been Proposed For The Wow! Signal?

By the time Ehman detected the signal and reported it, the Earth had rotated several times and Big Ear was not looking anywhere near the area of the sky. Indeed, owing to an oddity of Big Ear’s operation, there are two possible source locations, 3 degrees apart in Sagittarius. Attempts to scour the region, including one focusing on the most promising star in the area, have produced nothing. No signal like this has been detected since, despite the enormous increase in radio telescope operations.

The fact a comet was in the same region of the sky at the time has been offered as one possible explanation. However, the idea was quickly refuted, on the basis that it was not nearly close enough to the exact source of Wow!, and also covered far too much of the sky.

The most boring explanation is that the signal was terrestrial, perhaps reflected off space junk. After all, that is almost certainly the cause of the two subsequent signals that created some excitement, detected in 2015 and from Proxima Centauri in 2020.

There were far fewer satellites in 1977 than there are today, but the identification of what was known as the “Weird! Signal” in 2017 as coming from a geostationary satellite may also be relevant.

Atmospheric distortion of something more common has also been proposed, but no clear candidate has been identified.

All in all, the chances that we picked up signs of an extraterrestrial civilization so early in humanity’s search, and then found nothing since, are considered low. Yet the quest to find a natural explanation, or some form of human interference, has struck out so far.

Naturally, conspiracy theorists are convinced the Wow! signal was aliens, and that Big Telescope is hiding the truth. Yet the whole story counteracts their core perception of the world. The signal was revealed without any attempt at secrecy, and anyone is welcome to search the relevant part of the sky in whatever way they want, with no danger of men in black knocking at their door.