What is a radio telescope? How can we “see” with radio waves? Why are radio telescopes so large? Join Chris and Jonathan as they explore the nuts and bolts of radio telescopes.
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Hello everyone, and welcome to tech Stuff. My name is Chris Poulette and I am an editor at how stuff works dot com. Sitting here across from me. A guy who used to be an adventurer like you until he took an arrow to the knee is senior writer Jonathan Strickland. The sky above the port was the color of television. Tune to a dead channel. It's good guy, Okay, So um, before we get started, we're gonna do something we haven't done a little while. Yeah, we're gonna listen to a little listener mail. This listener mail comes from Minka, who says I love your podcast and have enjoyed listening to your incifle and quirky explanations immensely. I tried to search through the past podcast to see if you have done one on radio telescopes, to no avail, So I hope I didn't just miss it. It seems to me that radio telescopes are being used frequently to learn about this and study the far reaches of the galaxy and beyond, and it's pretty darn cool, so it'd be neat to learn more about how they work. Thanks and thanks for the show, Minka. Well you're welcome, Minga. I just wanted to say you're welcome, all right. So now we're moving on to our topic, the Smurfs. No No, we're gonna talk about radio telescopes. Yeah, we sort of. Well, we've talked about things that relate to radio telescopes like radio and set yes and set CD, which does very much relate to radio telescopes. Well, what do radio telescopes do? Why are they important? Well, it's funny that you should mention that, because they're my notes crashed, so I don't know what I'm talking about. I'm not I'm just kidding. They're still up. He can't see my computer from where he sits. Yes, because he's sitting directly across from me. Yes. See if if you ever wondered if that was true or not, it is. Yeah, um no, it's it's actually using It's unlike a typical visual telescope, which uses lenses and your eyeball and you look through it and you look for stuff on the other side and base it directs light which is in the visible spectrum of the electromagnetic frequency to our to our eyeballs. Ultimately right, right, But and again another drastic oversimplification of the parts. But a radio telescope is actually monitoring different parts of the electromagnetic frequency. Yeah, yeah, it's good looking at a completely different spectrum, So this is part of the spectrum that is not visible to the naked eye. So we are using these telescopes to measure um radio frequency variations that come from outer space. And it turns out that lots of stuff out there generates radio frequencies, right, So things like quasars, pulsars, galaxies, uh, distant stars, these sort of things can generate electromagnetic radiation and in the form of radio frequencies. And sometimes these are are objects that we can't detect visually, but we can detect them if we have a sensitive enough tool that can can detect and measure radio frequencies. So that's really what a radio telescope is all about. And it's kind of tricky picking up radio frequencies from outer space because only certain the actual band of frequencies or wavelengths I should say, the band of wavelengths that exist within the electromatic magnetic spectrum that our radio frequency waves. It's pretty broad, Yeah, about ten meters and to one millimeter. That's a pretty good size. Yeah, you can actually get radio waves that are even longer than that, like the size of football fields. But here's the thing is that the Earth has a level of the atmosphere called the iona sphere. Now, the iona sphere is uh, it's kind of funky. So you guys probably have heard us talk about ions before, you know. That's when we're talking about uh, atoms that have either gained or lost an electron. And if you ionize something, that means you've got some free electrons roaming around in it. So like an ionized gas or a plasma can actually hold carry an electric charge. Right, Yes, why are you smiling at me just because I saw a whole bunch of people going free electrons? Yeah, they're so expensive otherwise that's true. Have you seen my electric bill? Anyway? So you have the ionosphere, whether these free roaming electrons out there, and uh, and it kind of acts as a bit of a a shield or reflector in in some ways. And so radio waves of a certain wavelength cannot pass through the ionosphere. Essentially, anything that's ten meters are longer. The ionosphere is opaque to those. That's why you can actually broadcast certain long wavelength radio waves uh and bank them off the ionosphere, right because it won't pass through. Now, when you start getting shorter than a ten meter wave length, you have radio waves that can pass through the ionosphere. But if it's longer than twenty centimeters, which is about one point five gig hurts in frequency when you're talking about these, If it's longer than twenty centimeters, you start to have distortion as it passes through the ionosphere. It's called scintillation. And this isn't that different from the way when we look up into the sky and we see stars twinkling. That's sort of the same sort of thing we talked about being scintillating, same kind of idea, except in this case. You know, that's we're talking about the visual spectrum there, but here, Yeah, the twenty centimeters are longer, you run into that problem, and so that's not entirely useful for measurement purposes. So radio telescopes tend to focus on pun intended uh. Wavelengths that are between one centimeter and twenty centimeters in length tend to Now there are some variations, and also if you were to have a radio tell scope, say in orbit, where it's you know, you don't have the ionosphere as a in play. Um, that's a different story. But ground based radio telescopes kind of had to play within these rules because the way the ionosphere works. One of the nice things though about the radio telescope is that, uh, those frequencies generally come through pretty clearly. So uh, putting one of the ground based radio telescopes in orbit really wouldn't improve its ability to detect signals, UM, at least based on my research, not not within anything that's within those wavelengths. Yeah. Actually, it's it's a little tricky to detect that stuff anyway, because we're talking about really weak signals. I mean, by the time they reached the Earth, that these signals are not very strong at all. In fact, one one reference I I looked at said that, um that if you were to add up all the energy that every radio telescope on Earth had been subjected to since they were built, it still would not equal the energy would find in the snowflake. Yeah, that's pretty impressive. Actor. Now, grant that snowflake is the size of Detroit. No, I'm kidding, I'm kidding, typical snowflake. No. Uh. And it is also worthwhile to note, especially before anyone writes in UM, that radio telescopes do have to be placed away from population centers in general, uh, to some degree to because there is earthly interference. Yeah, those terrestrial radio interference that you have to try and minimize as much as possible. Otherwise it's just so much noise that you're not going to even find any signal out there, right right, So, um, yeah, it has its it has its good points and it's bad points simply because of the the frequencies it's able to monitor. And it's a good point too that you uh you mentioned the from the very first because these these devices. I mean, I imagine people you know, have a good idea what radio telescopes look like. I mean, we've all seen satellite dishes, and to some degree that's more or less what they look like. In fact, you may have seen pictures of them. But um, that I think gives it the this sort of feeling that it's a fairly recent thing. And in fact, um it was somebody in uh nineteen thirty three who who figured out that um there was uh, there were radio frequencies coming from extraterrestrial bodies, someone at of course Bell telephone laboratories. You always do that. I can't fight it that, I can't fight this feeling anymore. I can't. But yes, so you're talking about Carl Carl Jansky. Carl Jansky, Yes, uh. He he built the first antenna that could be used as a radio telescope back in nineteen thirty one, but it would take a couple of years to really figure out, uh, the fact that you could use this to to explore the heavens above. Because when he built his radio frequency detector, it was not to act as a radio telescope. It was meant to detect static that could potentially interfere with radio telephone services. Right. So he was he was working literally on a project for Bell. Yeah, And what happened was he discovered that there was this interesting hissing noise he was picking up and it was hitting a cycle. The hissing noise would would occur at a certain time every day, and the cycle hit, well, not every day, the cycle hit every twenty three hours and fifty six minutes. And once he removed the snake from the line, he realized there was something else hit. He figured out that the twenty three hours of fifty six minutes was essentially the period that it takes for if you've if you've got a fixed point on the sky for you to come back round, so that you're pointing at that same object. This will come up again later. Eventually he determined that this was the the origin of this radio frequency was otherworldly, so it was coming from outside the Earth, and that it was in fact coming from somewhere in the Sagittarius constellation far out. Yeah, so it would take a few more years before you saw anyone build a parabolic antenna, which is what Chris was talking about earlier, the dish style antenna. Those are not the only kind of antennas that are used in radio telescopes. It's probably, i would argue, probably the most iconic and the most common that we we see. But there are other types of antennas, including dipole antenna's, cylindrical parabolics, which are they kind of look like a trough. Uh. There are the yaggy antenna's, which are um not little guys who teach you how to use kung fu karate, I should say, their horn antennas, their mills crosses that kind of stuff. Mills crosses. Telescope is um various ways of doing this, but the principle is essentially the same. It's to try and gather to detect together as much as radio frequency um radiation as possible, and usually there are several reflectors involved that reflect radio frequencies to a focal point that can then send the signal to receiver and then from there it gets amplified. And we'll go through that process in a little bit. But uh so, in our and the parabolic style of of antenna, this is why you have that big dish. The dish part is actually reflecting um frequencies so that they all are directed to a single focal point and that's usually called the feed that's usually a small antenta called the feed that us often called the feed horn that will collect the signal and send it to the receiver. Yes, so these these radio frequencies are, like we said, generated by lots of different stuff out there in the in the in space. Um so. But the problem is that they're so so delicate. There's so such tiny little frequencies that you have to really control for the noise element, not just by trying to isolate the antenna of it, but also by making sure the material you've used in your antenna array is the right kind of stuff, because they're pretty sensitive things. And also the amount of information you can get is very much connected to the size of your antenna. Bigger antennas are able to provide a higher resolution image. It's kind of a weird word to say, because we're not talking about visible light necessarily, but an image of what it is you're looking at. Right. So, so the larger the better in general. But if you start building so large that the material itself is heavy enough to warp because it's it's it's so heavy that the structure itself can't maintain a specific shape, well then you're not reflecting the radio frequencies to that focal point anymore. You've warped it out of shape. So you have to build it out of special materials, and you have to plan for Okay, while uh, we know that by designing an antenna of this size, this particular warping is going to occur, so we have to factor that into the design so that the warping actually ends up helping rather than hurting. And usually you do that by adding a second reflector that is that's movable, so you can have a second reflector actually um position in such a way where the distortion from the main reflector hits the second reflector, which then reflects it back to the focal point, so it gets a little complicated. In fact, there are two main types of secondary reflectors. There's the Cassegrain focus, which is a reflector that's in front of the main antenna or the main reflector, i should say. And then there's another one if you have it in the back. It's called Grigoryan focus, and it chants a lot feeling you were going to say that, yeah, there was a pretty good chance. Uh, yeah, it's possible. Um. Now, given what what Jonathan was just talking about, giving the materials and and the uh, there are a lot of things that that can affect, uh, the efficiency of a radio telescope, including heat or cold, because the materials will expand or contract right wind the surface of the material itself, the surface of the material itself. Um. But other than that, I mean, once you take all these things into account, it is theoretically possible to build as large a radio telescope as you possibly can. There's really no limit to the size other than the fact that you're going to have to take things like gravity and temperature and things like that into a tensile strength. But conceivably, if you could build one that's three times the size of Earth, it would work. But that and that's fascinating because it's it's not it doesn't have to be a particularly large or particularly small device. It just you know, you can pick up more with it. And a lot of a lot of radio telescopes are actually telescope like antenna a rays, so it's not just one antenna's several antenna's working together in order for you to gather this information, and that that helps you create a larger radio telescope just but you know, you're adding extra elements in. It means that you sort of get around part of the problem, which is, you know, building just an enormous single antenna. You can do an array of antennas. There are different limitations on this as well. Um So the signal that you're picking up with this radio telescope is really really weak, So in order for you to have it and to to transmit first you have to you have to transfer the radio frequency information by by changing it into electricity. But because the frequency signal is so weak, the electric current would be pretty pathetic. You would not be able to measure it just by converting it right from radio frequency to electricity without amplifying it in some way. So typically a radio telescope will then have a pre amplifier. So you musicians out there and and and radio folks, you know, you're probably pretty familiar with the idea of a pre amplifier. Microphones usually have a pre amplifier, that kind of thing. Um, So a pre amplifier is really just a a way of boosting a signal a certain amount before it gets truly amplified, uh, for the final use of whatever that signal is gonna be, whether it's in the audio industry or in this case, the measuring the celestial bodies. Yeah, I was I was gonna say that they don't necessarily usually have them anyway. Um, well, that's that's fair, but it does it does assist, uh, and in picking up these weak signals, that's for sure. Yeah. And so the kind that tends to be used in radio telescopes are called low noise amplifiers because we're talking about such small, very very quiet and signals. And so, boy, I'm glad didn't do the old listener mail will be getting because then it with all this, it would have probly blown everybody's ears out. So the the these l n A pre amplifiers take these um signals and then they boost them now here's the thing. Any sort of interference at this point could really compromise the measurements you're making. So that includes molecular movement of the pre amp. So the fact that you know, everything in matter is made up of molecules, and these molecules move even in solid objects, right, So they in in a in big radio telescope facilities, things like the professional ones that you would find in say NASA, they tend to have to cool down the pre amplifier to reduce molecular movement as much as possible, and usually to around ten kelvin. It's pretty cold. Pretty cold, yeah, zero kelvin means no molecular movement. That's what like the deepest reaches of space would be zero kelvin. So ten kelvin's pretty cold. They tend to use liquid helium to cool down the this this device low enough so that it reduces the chance for it to contribute noise to this signal. All right. From there, the signal moves into a mixer, yes, where it has a party and networks with people and not. Oh, should have taken different notes. Okay, well I'll just work from memory here then. Um No, a mixer, what the mixer's purpose is to change the frequency of the signal. Now, these signals are very high frequency and UH, and it turns out that it's easier to amplify lower frequencies. It's possible to amplify higher frequencies, but in general, it takes less UH effort to amplify the lower frequency signals. And if it's kept at it's high frequency and you're just you're you're working with the frequency at that and it's native frequency, there's the chance that will travel back up the antenna and create feedback. It's not dissimilar to what would happen with a microphone too close to a speaker, where you get that wonderful sound that's not wonderful. Now you're you're probably more familiar with it than I am, with your rock and roll lifestyle and all. So then what happens is the mixer mixes this frequency, not just it doesn't just lower. The way it lowers this frequency is it mixes the frequency with a frequency generated by an oscillator. Okay, so the oscillator creates two frequencies that are both sent into the mixer and UH one is their polar opposites of each other, and So the the mixer adds in the lower frequency together with the frequency that came in through the receiver, and that is what it sends out to the intermediate frequency amplifier. So we've gone PREAMPTI mixer. Mixer pulls in a second frequency from the oscillator. The oscillator frequency, the lower one, gets combined with the incoming frequency that is then sent to the intermediate frequency amplifier or I of amplifier, and that just process that sesses that signal and amplifies it. We've talked about amplifiers before in this podcast, so I'm not going to get into that. Uh. And then this this stronger signal from the I F amplifier gets sent to Well, now we've got to go to the square law detectors and the d C processors because we have to create a d C a direct current in order for that to go to a recording device. So this converts the frequency from the amplifier to direct current signals, and it smooths out the signals to make them easier to measure because they fluctuate quite a bit. Even as direct current, they tend to fluctuate. So the way they do this is they use capacitors. And if you recall we've talked about capacitors before too, capacitors store up electricity and then release it all at once, right there. They're kind of like a battery that it can store electricity, but unlike a battery, it is and it releases all the electricity, doesn't do a constant flow. This, by the way, is the reason why it's a bad idea to fiddle around with electronics you don't know a lot about, including things like televisions and computers, because they have capacitors in them that can store high amounts of electricity that are potentially deadly. So, especially things like computers and televisions, you don't wanna, you know, just knock a hole in one, or you know, I've seen like videos, if you've ever seen a video of someone who who accellently breaks the television, you see a spark go off. That's a capacitor that's that's discharging, and those can be very dangerous. So anyway, in this case, the capacitors are used to kind of smooth out those signals. I have read an interesting analogy which said, imagine that you have a water hose and water is moving through the hose, but the pressure keeps changing, so the water sometimes it's flowing out very quickly and sometimes it's sputtering out. Okay. Uh. In the case of this detecting radio frequencies, you want to a steady um flow so that you can measure it properly. So what if you were to instead of just measure the measuring the water that comes out of the hose, you you direct the hose towards a bucket, okay, And at the base of the bucket there's a spigot that you can open up. Well, if you open up the spigot on the bucket, water is going to flow out at a much more steady rate than it's flowing out of the hose. That's the kind of idea here with the capacitor, and that it's to try and smooth out that signal and make it easier to record. And then finally you've got the actual recording device. Now, in the old days, the recording device was a an old man who said, what was that. No, it was actually a pen attached to a a movable arm and some paper that was pulled across and then the movable arm would would move depending upon changes in voltage and so it's very similar to uh, earthquake detecting equipment. We've talked about seismological equipment in the past where you see that or even if you think also similar things lie detectors. That's exactly what I was thinking. Polygraphs where they have the little the little pen that scratches back and forth across the papers, the papers going by, similar kind of thing. Um, now you were in October fourteen. Yeah, so we tell you when did you go super nova? Um? No, so this in this case instead, what it's doing is it's actually uh, modern ones don't tend to use this anymore. They tend to actually send the data directly to a computer where it gets recorded and you read out the information on a computer screen, as opposed to looking at a physical representation scratched out in pen um. That's generally how the radio telescope works from start to finish. So it's pretty interesting stuff. It's a little complex, I would say, yeah, yeah. Um. One of the things that we were talking about two Jonathan mentioned, um the Jansky's experiments where he was he would note that the interference would come around it these certain period of time. UM. One of the prime places to put a radio telescope is near the equator because it is really good. Um, it's a really good place to get an accurate depiction as the Earth rotates, um and it can it can identify sources of radio information coming from space very clearly. UM. Unfortunately, it's a rather expensive place to try to build a radio telescope, and that's one of the reasons why they can be found in many different places around the world. But yeah, closer to the equator tends to be better just for the you know, the quality of information you can get from this. UM and and uh, we've actually started using radio telescopes to kind of map out the celestial bodies around us, even ones that are not visible to the naked eye. And it's been very useful for astronomers. And there's still there's still even you know, uh, amateur astronomers who use radio telescope. This it's it's not just the realm of massive scientific organizations like NASA, although I mean those are the ones that you know, if you look up the pictures online, you tend to see the really larger arrays or really large antennas that belong to these major organizations. Now, a radio telescope is able to detect things celestial bodies in the sky by their angular resolution. Um. Basically it it really is contingent on the wavelengths that it is able to detect. So that's one of the reasons why, Um, a radio telescope does need to be large. Um. Yeah, if you you could build a small one, but it wouldn't be nearly as functional as a larger one. Basically, the larger radio telescope is the greater it's angular resolution. Um. But um, that that's basically, uh, that's basically what it is. What what it's using. In terms of how you would measure the effectiveness of a radio telescope. Yeah, if you you know, if you had like a backyard telescope visual telescope, the resolution you would get on that is equivalent to what you would get with a huge radio telescope. The resolution on a radio telescope is proportional to its size. So um, yeah, you've gotta have a big one if you're going to have any any real precise resolution. And again we're not. You know, it's it's a little weird because it's hard to think of resolution in terms of something other than visible light, because that's what we're mostly familiar with. But but yes, it's it still applies in this case. YEA UM and radio. Basically radio astronomers have been able to detect all kinds of different molecules in space too. UM. You can you might be surprised to learn. I was a little surprised to learn that radio radio astronomers were able to identify carbon dioxide, water, formaldehyde, ethyl alcohol, methanol, and na um and all kinds of other different kinds of just that kinds choice of compounds out in space UM and and to use the radio telescope in that way, I mean, it's you can get a lot of information. And that's actually uh sort of ties back into the set project because the if if you haven't listened to that particular podcast or are unfamiliar with the project, Basically, UM astronomers were collecting large amounts of data from the radio telescope. They were using UM for their project, and the thing is their computers couldn't analyze it all at one time. They were collecting so much that it was just stacking up essentially, not literally, but to figure it in to create an analogy we've talked about in the past, how on YouTube users are uploading forty eight hours of content every every minute, So it'd be like telling one person to watch everything that's on YouTube. You've got you've got a growing amount of content that you're never going to catch up to and only so much ability to consume it. So same sort of thing. In this case, we're talking about generating uh, incredible amounts of data and having a limited ability to actually analyze the information. So what they would do was to break it down and use it in a distributed computing project, which they were calling Steady at Home, and the idea being that people take a slice of information, allow their computers to work it out using a specially designed program, and send it back to the astronomers so that they could evaluate it and add it to the project. And uh, you know, it's just sort of a kind of a neat way to get into helping out with the project like that. But that's that's one of the problems, a good problem to have with with radio astronomy is that these uh large radio telescopes can couldn't collect an awful lot of data. Yeah, and so we might use them to discover things like quaysars and pulsars that we had never seen before, or even detect the presence of a galaxy that before this point we just didn't know existed. Uh. Now, Cetti, of course, was really looking for any sort of signals that might indicate a pattern or uh a possible um well possible hint that there's some sort of other intelligent life out there that's generating these signals, not not just some natural phenomenon. Do do do do well? Um and radio radio telescopes can also detect information about near celestial bodies as well. Uh, the surface for the Moon, we knew it was sort of sandy before people actually landed there because astronomers had used radio telescopes to uh to get signals from the Moon and learn you know what it was like. They're also Venus, you know, is shrouded by clouds, but astronomers are able to learn more about the surface by using radio telescopes and radar to get an idea of what the actual planet surfaces. Well, they've also used it to observe the storms on Jupiter, so that's kind of interesting too. Like they just looked at the weather report for to right today today it's gonna be a big gas. It sounds like my never mind, never mind, Yes, just think that. Okay, but yeah, I think, uh, it's it's an interesting topic. It's really and it's one honestly I did not know very much about before we started researching this podcast. No, I agree with you. I mean I knew of it, I knew it existed, but I didn't really understand what it was doing or how it did it. And it is pretty cool. I mean, it just shows me that radio is way cooler than I ever imagined when I you know, so there you turn a radio on. That's that's the extent of your Maybe you play with a walkie talkie, but that's about it as far as radio goes. And then the more you look into it, the more you're like, wow, this is really phenomenal stuff. Tesla was onto something. I'm gonna say you probably had a patent for that. Yeah, I probably did. And then never mind, I'm not gonna go into another Tesla rent. Okay. Then all right, Well that wraps up this discussion. Minka. Thank you so much for writing in and suggesting that that was a really cool topic for us to tackle. If any of you have a topic you would like us to look at in a future episode of tech stuff. You can let us know on Twitter or Facebook are handled. There is text stuff hs W and I promise we're gonna have a new email for you soon. We just haven't created that new email address on our new email platform. Um, you can try sending it to the old one, but there's no guarantee get to us. But as soon as we have a new one, I'll let you guys know. So that'll wrap this up and Chris and I will talk to you again really soon. This podcast is brought to you by audible dot com, the Internet's leading provider of audiobooks, both more than one dred thousand downloadable titles across all types of literature and featuring audio versions of many New York Times of sellers. To try Audible free today and get a free audiobook of your choice. Get an audible podcast dot com slash text us brought to you by the reinvented two thousand twelve camera. It's ready, are you