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Ep. 294: The Arecibo Observatory

Ep. 294: The  Arecibo Observatory

The mighty Arecibo Radio Observatory is one of the most powerful radio telescopes ever built – it’s certainly the larger single aperture radio telescope on Earth, nestled into a natural sinkhole in Puerto Rico. We’re celebrating the 50th anniversary of the construction of the observatory with a special episode of Astronomy Cast.

Show Notes


Transcript: Arecibo Observatory


Astronomy Cast episode 294 for Monday, February 18, 2013 – Arecibo Observatory

Welcome to Astronomy Cast, our weekly facts based journey through the cosmos. Where we help you understand not only what we know, but how we know what we know.

My name is Fraser Cain, I’m the publisher of Universe Today. With me is Dr. Pamela Gay, a professor at Southern Illinois University Edwardsville.

Hi Pamela, how are you doing?

Pamela: I’m doing well how are you doing Fraser?

Fraser: Good. Back from an epic two week vacation down the west coast of the United States. We went to Oregon, and San Francisco and Los Angeles. I went to Griffith Observatory, I went to Nassau, I went to Pixar, and the Natural History Museum. It was Aaaaaaawesome! And now I’m back.

Pamela: And you did all of this with your kids; and you crammed in business and life and everything else along the way.

Fraser: Yeah. Yeah, exactly. It’s a, it’s a business – a tax write off. Yeah! Umm, so no, it was good. It was really fun. If you’ve never done that trip; if you’ve never gone down the west coast of the United States, I highly recommend it. It’s a beautiful, chunk of the world.

Pamela: It really is. So is western Canada and Alaska. So really just like start up at the Bering Strait and, and, and …..

Fraser: …. drive, yeah, you pretty much can’t drive north of Vancouver along the coast like that.

Pamela: Really?

Fraser: Yeah. So, you got to take a ferry.

Pamela: Oh, well.

Fraser: So, you have an announcement this week.

Pamela: So I, I do. Uh, we had great success last fall teaching a series of different classes through Cosmo Quest. It’s our Cosmo Academy Program. And we are offering two more classes this spring. The first one is Stars and Stellar Evolution, or actually it’s called The Sun and Stellar Evolution, but it’s really Stars. This is going to be taught by our own Ray Sanders, Deer Astronomer. And that course runs from April 15th to May 8th. And you can sign up for it at Cosmo Quest dot org slash classes ( There’s a link to the EventBrite page.

And then we also have Dr. Matthew Francis who on Twitter is Dr. Mr. Francis. It’s really Matthew R. Francis, but it looks like Dr. MR Francis. Uh, he’s the Director of our Cosmo Academy Program and he’s in the process of writing a new book on Cosmology and bringing his expertise to the classroom. He’s going to be teaching an introduction to Cosmology Class.

Both of these classes are limited to just 8 people since this is a very intimate experience. And Nicole Gugliucci and I will pop in on a regular basis. And so if you are interested in learning and you have some spare money to take some classes…We’re sorry, we can’t do these for free.

Fraser: Yeah, there is a fee for these. Yeah.

Pamela: We have to pay our instructors. But these are chances to learn from people active in astronomy and who are solid communicators of astronomy. So please sign up and join in. And, I hope to see you in our classroom.

Fraser: It’s all done in ‘Google Hangouts’, right?

Pamela: Yeah, we do everything through Google Hangouts.

Fraser: Yeah, and, uh, that’s great. So there are only eight slots with each one and I know they’re going to fill up fast, so if that’s in anyway interesting to you, uh, go and sign up. Is there a different fee for each one?

Pamela: No it’s both the same fee and to be entirely honest in trying to figure out what to charge I looked at the typical prices of yoga, horseback riding, ballroom dancing and piano lessons….

Fraser: Right.

Pamela:…….and we are completely competitive with any other sort of extramural class you might take.

Fraser: Ok, so let’s get on with the show then.


Fraser: The mighty Arecibo Radio Observatory is one of the most powerful radio telescopes ever built – it’s certainly the larger single aperture radio telescope on Earth, nestled into a natural sinkhole in Puerto Rico. We’re celebrating the 50th anniversary of the construction of the observatory with a special episode of Astronomy Cast.

Fraser: Uh, 50 years!

Pamela: Yeah….

Fraser: Yeah.

Pamela: …. yeah. It’s, it’s kind of awesome that we’ve been building monstrous facilities like this for so long and it makes you really think back to the fact that 50 years ago, that’s not too different than time, it’s the same generation that built the Hoover Dam, that built the St Louis arch, that built all of these giant works programs across the United States. And one of these works programs was building a giant radar dish in Puerto Rico and it took about 10 years to sort out all the details what was needed and was finally opened in November of 1963. And we’re still using that sucker today. It’s constantly getting updated both on the software side, and as monies allow, on the hardware side that it continues to be a competitive facility capable of doing science that nowhere else in the world can this science get done.

Fraser: Now, this is a very special instrument, so can you sort of explain a bit about like what, like have you ever visited it?

Pamela: No, no I haven’t.

Fraser: No, no. Um, like, what is it? And I know we’ve seen it in movies and film and stuff. But like what is, what is the observatory? Because it’s pretty neat.

Pamela: Well, at the most basic level it’s nothing more than a satellite dish like you might use for getting television and internet. It is capable of both sending and receiving radio waves. But what makes it special is this sucker is huge. There is really no other way to put it. It is 300 meters, or a thousand feet in diameter. It is built into a natural sink hole in Puerto Rico, which is actually why we chose to build it there. You don’t want to have to build a hole for something like this.

Fraser: A thousand feet across, yeah.

Pamela: So they found a natural hole. And it’s a spherical mirror. Not mirror, but a spherical reflecting surface. And this is actually very important. When they were first working on designing this, the initial design was strictly to use it to study the atmosphere. And they were originally going to build a parabolic, a mirror that only focuses at a single place above the reflecting surface. And, that would mean that it could only observe straight up. Now that really limits what you can see especially since planets aren’t necessarily going to be directly above this object.

So, as the project continued to move forward, they actually put out a request for proposals on, ‘how can we redesign this so you can actually look at different parts of the sky without being able to move the dish?’ You can’t move a 1000 foot dish; a 300 meter dish. That’s a lot of mass. It would deform as you moved it.

Fraser: Right. (Laugh)

Pamela: So, (laugh) they built this beautiful system out of aluminum sheets. They are suspended on a network of cables. And, by switching from a parabolic mirror that only focuses on one place, to a spherical mirror that has the exact same image issues everywhere you point, you can actually over a spherical dish move your focus point around. Then as far as it’s concerned, there is still part of a sphere below it. But then you have to figure out, ‘how you suspend that thing you are moving around so you can move it so carefully, so gradually that you can track the earth’s rotation precisely. And the system that was eventually devised, there’s a series of pillars that was designed for them. We put up three because that’s what they realized was all they needed. There are these three towers that have cables coming in and they suspend the receiver for the system and they can move the receiver around on a series of tracks. And it’s all extremely precise.

And what’s really funny, is all of these bits and pieces have an acting role in the GoldenEye, James Bond movie. Except instead of pointing at distant quasars, they are pointing at nearby satellite that is going to blow up the earth, or something.

Fraser: Right. And they need to fight on these various parts of the observatory.

Pamela: Right. Right. It’s really kind of funny. (Laughter)

Fraser: So, this is a bit of a mega project. It was probably a very complicated and very expensive undertaking to make something that large. What were the original science goals of the observatory? What did they plan to use it for?

Pamela: Originally they were just looking to study the earth’s atmosphere. You can bounce radio signals off our atmosphere and depending on the wavelength of light, they will bounce off different heights in the atmosphere, and based on how they come back, you can measure the turbulence pockets; the cells of different atmosphere characteristics as it goes up. So it’s a very detailed way of observing all the different layers in our atmosphere. But then as they worked to redesign it to allow tracking and guiding, they added in the ability to do active radar, to bounce radar off of nearby planets the same way we might image a satellite orbiting the earth with radar or heck police radar beam things all the time.

Fraser: So you’re using it to transmit radio waves at a surface and detect the bounce back from the surface, which is amazing to be able to send. It’s a transmitter.

Pamela: And what’s kind of cool is up until Arecibo was up and working, we didn’t actually know accurately the rotation rate of the planet Mercury. It’s was only in 1965 that we realized this little world wasn’t as locked the way we thought it was. So it turned out we figured out from the radar returns that it rotates every 59 days instead it was previously thought every 88 days. So just a few years after its opening it was already completely changing how we looked at nearby planets. And, in fact it was the instrument that was able to provide us our first maps of the planet Venus. It met at only a resolution at 1.5 kilometers. But it still mapped Venus and radar light for us.

Fraser: But, you can’t move that observatory at all. You can only move that detector array that’s above it, right?

Pamela: Right.

Fraser: So, for example if they wanted to observe the surface of Venus, how would they do it?

Pamela: So luckily, they built this observatory fairly near the equator. Puerto Rico is a nice equatorial island. And that means that it’s looking up at that part of the sky that all the planets occupy for the most part; the sun and the planets all very back-and-forth from plus-or-minus, roughly 24 degrees in-between the tracks of Caprica and Cancer.

And luckily, this observatory, by moving the receiver around, the receiver is able to look at light that’s coming in at a different angle depending on where they put it. And by steering the receiver around, they can actually look at objects within plus-or-minus within 45 degrees straight overhead. That’s gets all of the planets and that gets them a good chunk of the sky. And truth be told, any observatory, you really aren’t going to be pointing the telescope more than 45 degrees down from straight overhead because you are just looking through too much atmosphere if you do that. So even though you can’t move the base of the telescope, you can move the receiver and still steer around the sky.

Fraser: So it’s possible to get the radio emissions from Venus, coming from Venus. They bounce off that spherical array up into the actual detector which has been positioned to get that image. But how do they actually look…….. (I’m putting in air quotes in video)

Pamela: (Laughter)

Fraser:………how do they look at Venus because it’s radio, right?

Pamela: Right. Yeah.

Fraser: So it’s not like you’re going to look through your eye piece at this radio image of Venus. So what are they actually seeing?

Pamela: It’s even crazier than that. What people don’t really think about with radio telescopes is this is a single pixel detector. You are looking….

Fraser: One pixel.

Pamela: One pixel.

So you have to move the beam around on the object and it’s by re-centering that one pixel over and over and over, you are able to build up the image. So it’s kind of a longer more elaborate process than what many of us are used to.

But with Venus the way they do it, they actively shoot radar beams at Venus, and then measure how long it takes for that signal to get back. And by shooting these beams of radar at Venus over and over and over, they can build up the elevation differences from place to place across the surface.

And one of the kind of frustrating things is this is a very powerful device so we could conceivably use it for more than just the nearest planets. But we’ve run into this problem, objects like Saturn, the amount of time it takes the radar signal to get back is soooo long, that by the time the light has gotten back, Saturn is no longer in the field of view of the telescope.

Fraser: Right, You can just imagine the math here. They are detecting elevation differences on Venus that could be a few, you know, whatever, a thousand meters less, probably, and they know it takes light four minutes, whatever, two minutes, to get to Venus and back, and Venus is moving, and Earth is moving, and Earth is rotating. I just can’t imagine how complicated for these people to do this work. It’s insane.

Pamela: It’s just geometry.

Fraser: It’s really, really, really complicated and advanced geometry.

Pamela: Yes.

Fraser: Yeah. So, kudos….

Pamela: (Laughter)

Fraser: So it’s map the surface of Venus. It’s determining the speed of orbit, the speed of rotation of Mercury. But I think when a lot of people see the Arecibo Observatory, they think Contact, they think Aliens.. –

Pamela: Right.

Fraser: …they think the search for life…

Pamela: And….

Fraser: So how has it been sucked into that project?

Pamela: Well, truth be told, it was actually used for the SETI at-home projects. So if you remember back in the 90’s there was software you could install on your Windows system that would go through when your screen saver was on and download information from the University of California at Berkeley, and then it would process that information on that computer. It was one of the first citizen science distributed computing projects.

And the software that was used has continued to be maintained, continued to be updated. That core software was called Boink. And, SETI at home spawned a variety of sister projects including Einstein at Home, which is going through that same data, the sum of which was taken with the Arecibo Observatory. And while not every survey is going to turn up aliens, in fact none of them have so far, what they are finding are pulsars. And so there is this of diversity of research that can all come out of the same data, all using distributing computing to get the job done.

Fraser: And did they find anything yet?

Pamela: No.

Fraser: Have they tried using it as a transmitter looking for aliens?

Pamela: They have.

Back in 1974 there was a message that was sent out in ones and zeros that included what can best be described as a really dorky image. I’m not sure how else to put it. It was called the Arecibo Message. And it is trying to communicate towards the globular cluster M13, which it admittedly, if the signal reaches M13? M13 is dead. So that was a strange choice of destination.

Fraser: It sounds like a ton of stars in there. So you never know.

Pamela: The thing is that it’s actually looking up out of the solar system, so there’s not that many stars between here and there compared to other directions they could have chosen. So it was a 23 pixel by 73 pixel bit map, “bit map image” which is harder to say than one would wish of chemical formula, of the telescope itself, of stick figures. It basically mirrored the highest revolution video games of 1974.

Fraser: Yeah, exactly. When you’re looking at this image, you’re really seeing something that looks like Space Invaders.

Pamela: Yeah. Yeah.

Fraser: So I think that’s pretty funny.

Pamela: Or a guy with his head in calipers of some sort. It’s very strange. (Laughter)

Fraser: Yeah, it’s a pretty funny image. But I think the point is they were trying to get across with as much information. They were trying to show the decimal system. They are trying to explain the planets we have, what we look like and what instrument we use to communicate this message. And they only coded it into this 8-bit image that would look appropriate on a video game. Pretty clever, I think.

On a complete side note, when I was at NASA JPL, I got a chance to see the golden record that’s attached to the Voyager spacecraft. And it’s that same concept. And there are also the ones that were attached to the Pioneer. But it’s that same idea. How do you communicate to space aliens anything? So you start with math. We understand pi. And we understand e. We understand these basic fundamental numbers and then try to build up from there. And the laws of physics will hopefully be the same for aliens as they are for us. So,….

Pamela: One hopes…

Fraser: One hopes. And that was the message in Contact, right?

Pamela: Yeah, and that was one of the awesome things about Contact. They looked at it from the perspective, ‘How do you actually break this down?” If someone were sending a signal, if we were sending a signal, what are the different things you would want to encode? And at a certain level you have to take advantage of the fact that transmissions can be a long multiple resonance of wave lengths that you can have signals encoded within signals at a certain way.

So if you think about it with television, they are encoding x and y positions of each little color for the television as well as the sound track and so there’s also the sub captioning. All of this encoded together. And so with Contact, there was at one level pi coming out; and at another level there was video coming out; and at another lever there was this great grand instruction manual. So Contact, Carl Sagan took the greatest extreme, ‘What are our hopes and dreams made manifest by another civilization?’ And he did base the lead character, the one played by Jodi Foster, on Jill Tarter who was the director of the SETI Institute she told recently when she stepped side ways to focus on getting the Allen Telescope array going and focusing on science. So it’s a very realistic depiction what it means to be a woman in science and what in it’s time we might have aspired for.

Fraser: Now, I know that there are, I mean, with the Arecibo Observatory you’ve got this strategy of one really big radio telescope, a super telescope and it’s the same concept with James Webb’s space telescope. Let’s just pour a bunch of money into something really big…the Hoover Dam of radio telescopes. But a lot of the work now in radio astronomy is with these arrays, these distributed arrays across the entire earth. Now can the Arecibo Ray join these global connections?

Pamela: It depends on what science is being done. A lot of the smaller dishes work at slightly different wave lengths as Arecibo, but when they are working at wave lengths or frequencies that are compatible, yes you can combine the like. It’s a pain. You have to do all sorts of things like what’s called fringe finding where you work to adjust the time separation between the different facilities. But yeah, it can join in.

The great thing about radio signal is you can combine it after the fact unlike optical light because we can actually record each and every incoming wave. We just can’t do that with optical light.

Fraser: Now because it’s an instrument telescope observatory in astronomy, I’m going to assume it is severely underfunded and constantly under risk of being cancelled…

Pamela: Yeah.

Fraser: …and disrepair. So, how is it doing on that front?

Pamela: Well it’s actually doing just fine. It is a jointly funded facility. It receives funding from National Science Foundation, from NASA, it’s administered by Cornell University. And the reason why it’s been able to survive, every time they try to cancel it, which happens on a regular basis, scrambling occurs and eventually someone steps up and somehow the money is received.

So for instance, in 2009 they were able to get 3.1 million from the stimulus funding that came out for shovel-ready projects. Just things like that keep happening over and over across time. And today the diversity of things it can do are such that it would be somewhat foolish to cut it off, so it’s done a good job at making itself required.

With that big of a surface area you can detect extremely faint signals you can’t detect with the distributed arrays of telescopes. The distributed telescopes have an amazingly high resolution. But each dish can only collect so much light. One giant dish can effectively listen for the weak signals of spacecraft all across our solar system.

It can also get used for active radar on asteroids; imaging asteroids and they pass by, which is kind of something we’re interested in considering asteroids can hit us. And it just has all of these different things they’ve worked on redoing the surface allowing it to go first down to a wave length of 60 centimeters; sorry 6 centimeters; then down to 3 centimeters. Then by getting to these very small wavelengths they are able to get increasingly higher resolution images because the resolution is determined by how many times the wavelength fits across the diameter.

So you have this great combination huge collecting area allowing you to see fainter and fainter objects; and huge size that as they are able to perfect the surface, and perfect the receivers, to detect shorter and shorter wavelengths. They are able to detect things at a higher and higher resolution.

Fraser: Yeah. When you hear of people talking about the fact they are going to shut something down or stop maintaining, you just kind of look at the enormous scientific instrument that cost hundreds of millions of dollars to build and is producing tons of amazing science, how on earth could they cancel that kind of project?

Pamela: Well….

Fraser: It’s the same thing when they talk about they’re going to talk about cancel Voyager and things like that, and you’re just like, “It was billions, it’s out in space, it sending back data still! You can’t cancel it. I’ll just pay for it. Ya’ know? I’ll take it over!

Pamela: How I wish.

The fundamental problem we’re running into though is NASA’s budget for the most part is getting flat lined for many years. And when you look at a flat budget in a situation where we do have inflation, you actually have a decrease in budget over time. Now take a decrease in budget, and now increase the number of facilities that are trying to draw funding from that budget, and what you have is something has to give and it’s turning out they’re doing things like restricting travel, restricting conferences, making staff work more hours because there’s simply fewer staff to accomplish the same amount of work.

Eventually something is going to have to close. And right now we’re in the process of trying to figure that out. Arecibo seems to be safe but long term it won’t necessarily stay safe simply because as we add the large synoptic survey telescope, and telescope after telescope, add a comma – this all eats away at our declining resources. And it’s the people who are getting fired every time we try and save a telescope, which means if you’re a scientist, you do the science with these amazing instruments.

Fraser: Right. So do you think there’s going to be a follow-up observatory like Arecibo? Do you think there will be something else ever built like it?

Pamela: No. I don’t see this happening. I think this is because we’re trying to focus more and more on different types of telescopes. The Square Kilometre Array that’s getting built partially in South Africa and partially in Australia is going to be looking at extraordinarily long wave lengths using distributed array network, distributed antenna networks, spread out across multiple countries in South Africa actually.

The Add a Comma telescope is looking at the shorter wave length parts of the sky. And so as we build new facilities they are being built to have capabilities that complement Arecibo but don’t replicate it. So we’re trying to diversify what we can do and Arecibo is unique and fills a unique niche and as long as it keeps working we’ll build different things that add to what we can do.

Fraser: So for example we’ll go and build the big observatory in that big crater on the moon.

Pamela: That is something people try and bring up as a potential idea to do. It would have the advantage of being sequestered from the radio signals coming from the surface of the planet earth, if you build it on the far side for instance. But right now the funding necessary to do that is…

Well Charlie Bolden came out and said in the past couple of days, (he’s the current administrator of NASA), he said the United States will not be the primary country on the manned mission to the moon in his lifetime.

Fraser: Whoooooooa!

Pamela: Yeah.

Fraser: That’s sad.


Pamela: So, I kind of doubt we’re going to be having the manpower to go build these mammoth facilities. Now some other nation might. But I haven’t heard it talked about.

Fraser: Well, “Happy 50th Anniversary, Arecibo. And thanks for all the signs and all of the amazing backdrops for all of those cool movies. So we really appreciate it.

Pamela: And it doesn’t ever fill with water. It has a perforated thing so that in that whole thing they fill with water. No! And it’s not in Cuba, it’s in Puerto Rico. And it’s been in many, many other bad sci-fi movies. So we realized that we didn’t acknowledge things like Survivor – not the TV show, but the movie. And we know it’s been in a whole bunch of different books including one, my favorite The Sparrow by Mary Doria Russell.

Fraser: You can do a search in the internet movie database for Arecibo and it will show up every movie that’s it’s been an actor in. So, awesome. All right. Well thanks, Pamela. We’ll talk to you next week.

Pamela: My pleasure. Thank you.


This transcript is not an exact match to the audio file. It has been edited for clarity.

3 Responses to “Ep. 294: The Arecibo Observatory”

  1. Shauny says:

    Hi, theres no audio player or download link

  2. Nancy says:

    Try again! The player should be visible, or click on “Ep. 294: The Arecibo Observatory” to download.

  3. ullrich fischer says:

    Why isn’t someone building another radio telescope in the Meteor Crater in Arizona? It could be 1200 m in diameter and could be computationally coupled with Arecibo to get a huge baseline. Surely the Barringer family is tired of keeping it up as a tourist attraction by now and if not, it would be an even more compelling tourist attraction as an observatory.

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