The WOW! Signal

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Podcast Transcript

On August 15, 1977, for a period of 72 seconds, the Search for Extraterrestrial Intelligence had its greatest moment. 

A signal was received like none other before or since. 

However, in the over 45 years since the signal was recorded, astronomers have been unable to relocate it or even figure out what it was. 

Learn more about the WOW! Signal, why it was important, and what it could have been, on this episode of Everything Everywhere Daily.

In a previous episode, I discussed the Search for Extraterrestrial Intelligence or SETI Project. 

To very quickly summarize, SETI was established to try to find signals from extraterrestrial civilizations using radio astronomy. 

Why try to detect civilizations using radio waves?

Different wavelengths of light travel through space differently, and if you remember back to my episode of the electromagnetic spectrum, radio is just a form of light.

While space is a vacuum, there are gas and dust molecules that can inhabit interstellar space, which can block or absorb certain frequencies. 

There are certain frequencies in the microwave range, from about 1 to 10 gigahertz, which can pass through relatively unimpeded.

Frequencies above this range tend to get absorbed in the atmosphere or in interstellar space.

Frequencies below this range tend to be drowned out by the enormous amount of radio waves created by the core of the galaxy. The noise in this region is so great that it would be difficult to filter out a real signal from the noise. 

This band where communication would be possible, not being drowned out and not being absorbed, is known as the Microwave Window.

So, if we were to communicate with some civilization far away, this is the most likely place to check for messages. 

Simply looking for radio waves really isn’t enough, however. 

Back in 1967, radio astronomers Jocelyn Bell and Antony Hewish discovered something unexpected. They found something at the same point in the sky that pulsed with a signal every 1.337 seconds. Its signal was so regular that it was actually more accurate than atomic clocks at the time.

At first, this was thought to be a signal from an extraterrestrial civilization. However, they soon found others like this, and they realized it was a natural phenomenon. 

What they found were dubbed pulsars, which stands for pulsating radio source. They result when an extremely rapidly spinning neutron star emits radio waves from its magnetic poles. It is basically like a rapidly spinning lighthouse, and we can only see the signal when the beam of light hits us. 

In addition to spinning rapidly, they also tend to emit radio waves over a rather large region. In fact, spewing radio waves over a large band of the radio spectrum is pretty much a hallmark of naturally occurring radio sources.

When humans broadcast radio waves, we tend to do so over a very narrow band of frequencies. That is why you can listen to different radio stations so close to each other on the dial. 

So, a good place to look would be in the Microwave Window, and a good thing to look for would be some sort of narrow-band communication. 

However, there is one other thing.

The microwave window is still pretty big. 1 to 10 gigahertz is still a lot of spectrum to search. 

Within that window is a smaller range of frequencies that hold special significance. 

Hydrogen is the most abundant element in the universe by a wide margin.  When excited, hydrogen can emit electromagnetic waves at 1.420 GHz at a wavelength of approximately 21 centimeters.

Another important molecule is the hydroxyl molecule which consists of one oxygen and one hydrogen. It has a wavelength of 1.612 GHz to 1.720 GHz

What do hydrogen and hydroxyl molecules make when you put them together? Water. 

This range from 1.42 GHz to 1.72 GHz is known as the watering hole. This is a relatively short range of frequencies in the microwave window that correspond to two very important and common substances: hydrogen and water. 

I mention all of this because there is a very specific place where astronomers are looking, and there is a very specific thing they are looking for. They aren’t just randomly listening to everything in the sky.

If there is some extraterrestrial civilization trying to send messages, a narrow band signal somewhere in the watering hole seems like a very good place to search. 

With that, the story now turns to Ohio State University. In the 1960s, they created one of the largest radio telescopes in the world, known as the Big Ear. 

If you’ve ever seen a radio telescope or a photo of one, the Big Ear looks nothing like it. 

The Big Ear was the size of a football field. On one end was a 33-meter-long flat structure that could tilt up and down, but not right to left. 

On the other end of the field was a parabolic structure that didn’t move. In between, the field was covered in tin foil, and in the middle, there were two radio receivers. 

The way it worked was that the flat end would bounce radio waves from space toward the parabolic structure. The parabolic structure would then focus the radio waves into the radio receiver. 

The difference between it and a parabolic antenna was that you couldn’t point it anywhere you wanted. You could only adjust it up and down. 

However, that was fine because you could use the rotation of the Earth to move it right and left, over time.

The Big Ear was designed to conduct a survey of radio signals over the entire sky. The reflecting section would be set at a particular angle, and the Earth would revolve about its axis, allowing an entire strip of sky to be analyzed.

They could adjust the angle and do it again. They could just keep doing it until the entire sky was covered. 

That is exactly what they did. From 1963 to 1971, the Big Ear conducted the Ohio Sky Survey. They discovered almost 20,000 radio sources during the survey.

Once the survey was completed, the Big Ear was no longer a state-of-the-art instrument. Rather than dismantle it, in 1973, it was repurposed for the search for extraterrestrial intelligence, or SETI.

The events which are the subject of this episode took place on August 15, 1977. 

The way the system worked was that the radio telescope would listen for about 10 seconds near the 1.4 GHz frequency. An IBM 1130 computer would then take 2 seconds to analyze the data. It would then output a single alphanumeric character to indicate the strength of the signal to the background noise. 

If the signal it heard was between zero and one standard deviation from the background noise, it would just print a space. If it was between 1 and 2 standard deviations, it would publish a 1. 

After 9, it used the letters of the alphabet. A was 10, B was 11, and so on. 

It would print out the results, which humans would then analyze to look for any patterns. Most of the printouts were nothing but spaces and ones, with an occasional two or maybe a three. 

Several days after the recording took place, a SETI volunteer physicist by the name of Jerry Ehman was reading the recordings taken on August 15 at 10:16 pm Eastern Daylight Time. 

On the printout, amongst the spaces, ones, and twos were six consecutive characters that had never been seen before, 6EQUJ5.

This was an enormous, narrow-band signal located right near the 1.4 GHz frequency. The exact thing that SETI researchers were looking for.

Jerry Ehman took a pen and circled the data on the printout and wrote next to it…..WOW!  

Hence the name, the WOW Signal.

I should note that 6EQUJ5 was not some code that was sent by aliens. 6EQUJ5 just how the system used recorded the strength of the signal. 

The six characters represented a full 72 seconds of the signal. The “U” part of the signal was the point where the signal was a full 30 standard deviations above the background noise. 

There was no known natural way for a narrow-band signal of that strength to be sent.

So, the first question was, where did that signal come from? 

At the time the signal was recorded, the telescope was pointed toward the constellation Sagittarius in a particular section near Messier object 55.  Messier objects are points in the sky that are not stars and are usually nebulae or other galaxies. They will be the subject of a future episode. 

The area the signal came from couldn’t be pinpointed exactly due to the dual receiver setup of the Big Ear. However, in the part of the sky, we can narrow the location down to contains over a million stars. 

While we know roughly where the signal came from, the big question is, what was it?

If there was any information contained in the signal, it couldn’t have been recorded because that wasn’t what the radio telescope was set up to do. Information in a radio signal would be sent through modulation, and as the system was set up to average everything out over 10 seconds, the modulation would have been lost.

No other radio telescope has ever detected anything like this in that area of the sky. There have been at least 50 different attempts to find the signal in the same patch of space. In May 2022, several radio telescopes were pointed at this patch of sky for an extended period of time, and they found nothing. 

One theory holds that this was, in fact, some sort of extraterrestrial signal, however, whoever sent it is sending the signal out like a lighthouse beam. They are covering the sky, and our observation sweeping the sky just crossed their beam at the right point for only those 72 seconds. 

If this is the case, then why haven’t we seen the signal since then? One problem could be that we are only looking very intermittently. One of the longest searches was conducted by the Very Large Array in New Mexico, which only looked for 14 hours. 

One proposed theory that made the news back in 2017 was that it could have been a comet that it saw. That theory has pretty much been discredited because it wasn’t actually in the part of the sky at the time of the recording, and comets don’t behave that way. 

The other theory, which seems most likely, is that it came from some human source. The 1.427 GHz frequency is supposed to be dedicated to radio astronomy. However, it is possible someone was broadcasting in that part of the spectrum, even accidentally. 

It could be that there was some piece of space junk that reflected a radio signal which was picked up by the ultra-sensitive instrument. 

The truth is…..we don’t know. 

All we do know is that for one brief moment in 1977, the exact sort of strong narrowband signal, at the exact frequency astronomers were searching, was recorded. 

…and since then, it has never been seen again. 


The Executive Producer of Everything Everywhere Daily is Charles Daniel.

The associate producers are Thor Thomsen and Peter Bennett.

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