Sciency Words A to Z: Wow! Signal

Welcome to a special A to Z Challenge edition of Sciency Words!  Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms.  In today’s post, W is for:


There’s a ton of radio noise in space, coming from stars and nebulae and black holes and so forth.  There’s so much radio noise that it can easily drown out the relatively weak radio and television broadcasts that might be coming from a planet like Earth.

So if aliens want to talk to us, they’re going to have to send a much stronger transmission, something that will come through loud and clear over all that other space noise.  And in 1977, astronomers at Ohio State University picked up exactly that kind of signal.

As the story goes, Ohio State was conducting a SETI search with their “Big Ear” radio telescope.  The telescope recorded electromagnetic emissions coming from space, reporting the strength of those emissions on a scale from 0 to 9. If Big Ear happened to pick up anything stronger than a 9, it represented that with a letter—A represented a 10, B represented 11, and so forth.

On the morning of August 18, 1977, astronomer Jerry Ehman was reviewing Big Ear’s latest data when he saw a bunch of large numbers, and even a few letters.  Famously, Ehman circled those letters and numbers and wrote one word next to them: Wow!

Image courtesy of Wikipedia

Appropriately, this is now known as “the Wow! Signal” (the exclamation point is usually included in the name).

In one sense, the Wow! Signal is exactly what SETI scientists were hoping to find.  Even the radio frequency—approximately 1420 megahertz—was consistent with expectations.  In this 1959 paper, physicists Giuseppi Cocconi and Philip Morrison singled out 1420 MHz as the frequency extraterrestrials were most likely to use.

But in another sense, the Wow! Signal was not what we wanted it to be, because it only happened one time, and it has never repeated since. Despite many follow-up searches of the constellation Sagittarius (like this one or this one), where the Wow! Signal originated from, we’ve never picked up a signal like it again.

As I’ve said several times this month, in our search for alien life, we have to hold ourselves to the same standards as a court of law: proof beyond a reasonable doubt.  The Wow! Signal very well might have been aliens… it might have been anything… and that’s the problem.  Unless and until we pick up the Wow! Signal again, we can’t prove one way of another what it was.

Next time on Sciency Words A to Z, you can’t have life without water.  Or can you?

10 thoughts on “Sciency Words A to Z: Wow! Signal

    1. Well, you may be right about the courts. But too often when people hear that something “could be aliens,” they think that means we’ve totally found aliens. So for my A to Z series, I really want to drive home the point that so long as we still have alternative hypotheses—reasonable doubts, in other words—we can’t say for certain that we’ve detected alien life.

      Liked by 1 person

  1. Ok, not to be troublesome, but… are we reaching to expect that another lifeform is going to try and contact us in a manner we will recognize? How could they know we expect them to repeat the signal over and over again?

    Liked by 1 person

    1. Fair point! I wanted to get into this, but it would have made this post too long. We’ve sent several transmissions into space ourselves, like the Arecibo message. But those were only one-time things. So how do we know someone in Sagittarius wasn’t doing exactly what we’ve been doing?


  2. I think SETI is a long shot, but I’ve always been impressed by their intellectual honesty. They’ve been compared to paranormalists, UFOologists, and other pseudoscientific activities, but as far as I can see, they’ve never claimed to have found anything they can’t back up with data. Their treatment of the WOW signal is a prime example.

    On radio noise, my understanding is that the 1420 to 1670 range is thought to be likely because it’s an unusually quiet range, referred to as the “water hole” by radio astronomers. The problem is that, for bandwidth reasons, the aliens may be using something like lasers (possibly in the visible, xray, or even gamma ray range) that we’d only detect if we happened to be in the line of sight. Still, if they’re trying for first contact, the 1420-1670 range makes more sense than it’s often given credit for.

    Liked by 2 people

    1. I agree with you: SETI scientists are doing really good science, and I think they’re good at not letting wishful thinking cloud their objectivity.

      I’ve read several articles and papers now about the hydrogen line at 1420 and the whole galactic watering hole idea. The logic of it does make sense to me. But some of those early papers on the topic seem so confident that aliens would absolutely, positively use those frequencies… in hindsight, that seems presumptuous to me.

      Liked by 1 person

    1. I don’t know if I’m qualified to answer that, but I think the problem is that the Wow! Signal only happened once. So from a statistics point of view, we only have a sample size of one.

      Something similar happened with LGM-1. When LGM-1 was first detected, it looked like it was probably an alien signal. That’s sort of where we are right now with the Wow! Signal. But as soon as we started finding other radio pulses like LGM-1, it became a lot easier to figure out what LGM-1 really was.

      In the case of LGM-1, it turned out to be a natural phenomenon (which we now call a pulsar). In the case of the Wow! Signal, we can’t say much for sure unless and until we hear it again.

      Liked by 1 person

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