How the Sun Works

Announcer: Welcome to Stuff You Should Know from

Josh Clark: Hey, and welcome to the podcast. I am Josh Clark. That is Chuck Bryant. Charles W. Bryant is not very happy right now. I'm to handle this, okay, Chuck?

Chuck Bryant: The whole thing?

Josh Clark: No. This disclaimer!

Chuck Bryant: Okay.

Josh Clark: As we proved with our Large Hadron Collider podcast, Chuck and I are not physicists.

Chuck Bryant: By the way, it doesn't shoot light, we found out.

Josh Clark: Speaking of light, we're about to talk about sun. I just want to say that Chuck and I are not astrophysicists either. We're just a couple of guys who like to drink some beer and, you know, just talk, just rap.

Chuck Bryant: I thought I was an astrophysicist until I read the sun article. Then my brain melted and oozed out my ear.

Josh Clark: You thought you were an astrophysicist?

Chuck Bryant: Eh.

Josh Clark: You were way off.

Chuck Bryant: Way off.

Josh Clark: So we're going to talk about the sun. If we get the Theory of Relativity - actually, no! We can't screw that one up. It's too famous. If there's a little thing here or there and you're an astrophysicist, please feel free to send us an email correcting us. We love that.

Chuck Bryant: That's the first time we've ever called for corrections before we started a podcast.

Josh Clark: It is. I think this one's appropriate. Let me start, Chuck. Have you ever heard of the sun?

Chuck Bryant: Yes, Josh.

Josh Clark: All right.

Chuck Bryant: I wish we had more of it these days in cold Atlanta.

Josh Clark: It is. It's a little chilly. If you'll notice, it snowed here.

Chuck Bryant: It did?

Josh Clark: If you'll notice though, after a couple of days of sunlight, the snow receded. Do you know why?

Chuck Bryant: No.

Josh Clark: Radiation. Heat!

Chuck Bryant: Yes. Energy!

Josh Clark: From the sun.

Chuck Bryant: Right. The sun, which, Josh, is one of over 100 billion stars! It's just a star.

Josh Clark: It is, and not even like a giant star either. It falls a little above average size. Did you know that?

Chuck Bryant: Should we talk about the size?

Josh Clark: Yeah.

Chuck Bryant: If there's one thing I can do, its read stats.

Josh Clark: Yeah. This is a very stat-heavy article, so it should be up your alley.

Chuck Bryant: Josh, the sun's radius is about 432,000 miles.

Josh Clark: Yeah. It's 109 times the radius of the earth.

Chuck Bryant: Yes, 109. Exactly!

Josh Clark: Which, I was like, "Wow. That means it has 218 times the diameter." No. That's not true.

Chuck Bryant: It's still 109. It's constant. NASA broke it down, our good friends at NASA, into something I understand which was if you think of the earth, the width of an ordinary paperclip is the earth's radius, let's say. Then the sun's radius would be roughly the height of a desk.

Josh Clark: Yes. I know this one.

Chuck Bryant: And about 100 steps from each other. Is that what you were going to say?

Josh Clark: That was what I was going to say.

Chuck Bryant: Sorry.

Josh Clark: That's all right. That kind of puts it into perspective. The sun's a hell of a lot bigger than the earth.

Chuck Bryant: Much bigger.

Josh Clark: And it's pretty far away. How many miles did you say?

Chuck Bryant: Eight light minutes.

Josh Clark: Which is apparently 92 million miles and change?

Chuck Bryant: Right. To put that into perspective, other stars are light years away, not light minutes away.

Josh Clark: Right. Since this is a stat bonanza, can I take a shot at one?

Chuck Bryant: Please.

Josh Clark: You said that the sun was how many light years, 25,000 light years from the center of the galaxy?

Chuck Bryant: Yes, sir.

Josh Clark: It takes about 250 million years for the sun to do one revolution around the galaxy.

Chuck Bryant: Can we stop here? I feel really good about it so far.

Josh Clark: I'm feeling good about it, too, Chuck. Let's soldier on, shall we?

Chuck Bryant: Yes. The sun is a G2 type star based on its temperature and the wavelengths of light that it emits.

Josh Clark: Right. It's about four and a half billion years old, which makes it a Population 1 star. Apparently there are two types of stars as far as age classification goes.

Chuck Bryant: I didn't know that.

Josh Clark: Population 1 stars are the younger stars, which include our sun. Population 2 stars are older. They think there was a third population, but none of them are around anymore.

Chuck Bryant: Right. Population 3!

Josh Clark: Right.

Chuck Bryant: They should just go ahead and claim that.

Josh Clark: Why not? We wouldn't know. We'd be like, "Oh, okay."

Chuck Bryant: Nobody would ever know.

Josh Clark: Luckily, NASA is very honest and forthright. Thank you, NASA.

Chuck Bryant: Thank you, NASA.

Josh Clark: Like we said, the sun is about four and a half billion years old. Humanity arrived at about the halfway point in the sun's lifetime. It's got about five billion more years worth of fuel.

Chuck Bryant: Which is good news?

Josh Clark: It is.

Chuck Bryant: For us. At the end of that run, it's not good news for us.

Josh Clark: We'll get to that. That will be the grand finale. How about that?

Chuck Bryant: Exactly.

Josh Clark: Chuck, what is the sun?

Chuck Bryant: Should we talk about the parts of the sun?

Josh Clark: Okay.

Chuck Bryant: Or do you just want to talk about the fact that it's a big ball of gas?

Josh Clark: I think we should mention that. If you talk about what the sun is, I think it's easier to understand its different components, and then in turn what it is.

Chuck Bryant: Okay. It's made up entirely of gas, Josh.

Josh Clark: Which is weird because gas generally doesn't form a ball and hav e an atmosphere and all that stuff?

Chuck Bryant: I know why, though.

Josh Clark: Why?

Chuck Bryant: Because of the extreme gravity.

Josh Clark: And heat.

Chuck Bryant: And heat. Holds everything together!

Josh Clark: Which is crazy? This extreme heat actually takes this gas and converts it into what is technically a fourth state of matter. You've got solid, liquid, gas, and plasma. Plasma is a type of gas that behaves in a way where it responds to magnetism. Generally, people just say its gas, unless you want to get really technical. Then you'll call it plasma.

Chuck Bryant: That's what NASA said. Scientists will only even sometimes call it plasma.

Josh Clark: The core, which we'll talk about in just a second, is so dense thanks to the force of gravity that it makes up two percent of the sun's volume, but it counts for half of the density of the entire sun. The gravitational field in the core is so strong that it pulls hydrogen atoms together in a nuclear reaction, a fusion reaction, which is where everything begins. This is where everything is accounted for, for the sun. Right?

Chuck Bryant: Yes. And a fusion reaction, if you guys don't know, is when two atomic nuclides join together and create a new nucleus.

Josh Clark: The key element, I guess, in the sun's nuclear reactions. That's all it is. It's not burning, like we consider a wood fire to be burning. It's a huge nuclear reaction. That's what the sun is. The key element is Helium-4. It has actually less mass than the two hydrogen atoms that originally began that set off this chain reaction that led to the creation of Helium-4. Since energy can be neither created nor destroyed, it has to be displaced. Under Einstein's Theory of Relativity, which we won't screw up here, energy equals mass times the speed of light squared. You can describe how much energy is created, right?

Chuck Bryant: Yeah.

Josh Clark: So when the mass is displaced, when this Helium-4 atom is created, the mass is displaced and it transfers into energy.

Chuck Bryant: I'm wondering how many of our commuters right now switched this off and put on Howard Stern on Satellite radio.

Josh Clark: Right. My fingers are bleeding right now. I'm hanging on barely right now.

Chuck Bryant: You're doing fine.

Josh Clark: Thanks buddy. So are you. So that's the core. It's the center of the sun.

Chuck Bryant: Yes. It extends to 25 percent of the sun's radius, just so you know how big that is.

Josh Clark: Right. And it's hot, hot, hot. It's 15 million Kelvin, which is really hot.

Chuck Bryant: Trust us.

Josh Clark: That's at the center. Like you said, it's 25 percent of the radius. What's outside of that?

Chuck Bryant: Just outside of that is the radiative zone. That extends about 55 percent of the sun's radius from the core.

Josh Clark: Okay. So these Helium-4 atoms are created. Remember, they create energy - or they displace energy when they lose their mass. It translates into energy. That energy starts traveling outward, and it hits the radiative zone. The type of energy that's created can be gamma rays, X-rays, whatever. Technically, all of these are light waves, so they're carried in these discreet little packets called photons, right?

Chuck Bryant: Yes. They're carried by the photons. The photon travels only about one micron, which is a millionth of a meter, before it's absorbed by a gas molecule.

Josh Clark: Right. Then this photon, which is absorbed by the gas molecule, heats the gas molecule up. Then the gas molecule spits out another photon, which is technically the same one because it's the same wavelength as the original photon, right?

Chuck Bryant: Right. It just repeats itself.

Josh Clark: Then it goes another micron until it's absorbed by another gas molecule. This keeps going on and on and on. By the time the photon escapes from the radiative zone, it averages about a million years from the time it was created, you could say, from the creation of that Helium-4 atom - a million years for one photon of light to travel this short distance.

Chuck Bryant: Yeah. That would be ten to the 25th absorption and reemissions taking place.

Josh Clark: That's a lot.

Chuck Bryant: That's a lot of zeros.

Josh Clark: That's actually, I think, 25 zeros.

Chuck Bryant: Exactly.

Josh Clark: Maybe 26. Once it escapes the radiative zone, it hits the convective zone.

Chuck Bryant: Right. That is the final 30 percent of the sun's radius, basically.

Josh Clark: It takes a little while for that same photon to escape that area, right?

Chuck Bryant: It takes 100,000 to 200,000 years to reach the surface of the sun.

Josh Clark: Yes. What's crazy is this. Once that one photon escapes the surface of the sun, it takes eight minutes to reach the earth's surface.

Chuck Bryant: That's pretty quick.

Josh Clark: Remember, its eight light minutes away, and light travels at the speed of light, so it takes eight minutes. But the sunlight that's hitting us when we go outside are made up of photons that were created more than 1.2 million years ago.

Chuck Bryant: I can't even comprehend that.

Josh Clark: Isn't that awesome?

Chuck Bryant: That is really, really cool.

Josh Clark: So we've got all these ancient photons bouncing off us. Let's get back to the convective zone. This is this area made up of these alternating areas of rising and cooling gas.

Chuck Bryant: NASA once again breaks it down a little easier. It's boiling convection cells, basically.

Josh Clark: Right. It looks like a pot of boiling water.

Chuck Bryant: Sure.

Josh Clark: Except these are gas, plasma.

Chuck Bryant: And there's no pot.

Josh Clark: No. There's only the sun. So we have the three parts of the sun. We have the core, the radiative zone and the convective zone. Now we've reached the atmosphere. The sun actually has an atmosphere.

Chuck Bryant: Yes, it does.

Josh Clark: Yes, it does.

Chuck Bryant: That's made up of three parts as well.

Josh Clark: Right.

Chuck Bryant: The photosphere, the chromospheres, and my favorite - I think everyone's favorite - the corona.

Josh Clark: I like the corona, which can only be seen in an eclipse.

Chuck Bryant: The corona gets all of press.

Josh Clark: It does.

Chuck Bryant: Josh, are we in the photosphere?

Josh Clark: We are. It's hot.

Chuck Bryant: That is the lowest region in the sun's atmosphere, and that is the region that you can actually see from Earth. That's where you can start to see things.

Josh Clark: Right. Actually, the photosphere is what gives the sun its round, crisp edge because as you travel outward to the outside of the photosphere, the gas is cooler, which creates that crisp edge we see for the sun.

Chuck Bryant: Right. It has an average temp of about 5,800 Kelvin, and it is 180 to 240 miles wide. That's big.

Josh Clark: It is big. After that is the chromosphere, right?

Chuck Bryant: Right. That's outside the photosphere, obviously.

Josh Clark: It's about 1,200 miles above the photosphere.

Chuck Bryant: Right. That's about 4,500 degrees Kelvin; so obviously, you'll notice that it's getting cooler as you expand outward.

Josh Clark: Right. But they think it's heated by the photosphere, and this churning gas, the convection cells, are still present in the chromospheres as well. Basically, what we're seeing so far is the sun is a nuclear reactor. At its core, gravity is pushing things together, and then they're exploding outward.

Chuck Bryant: Okay. I'm with you. I sort of misspoke because actually, the temperature does rise across the chromosphere, and it can rise to 10,000 Kelvin, which is even hotter than the photosphere beneath it.

Josh Clark: Right. Then we have the corona, Chuck, your favorite.

Chuck Bryant: Yeah. That's the final layer, Josh. It extends several million miles outward from the photosphere. You can see this. In fact, I think they first discovered the corona during the first solar eclipse.

Josh Clark: They were like, "What the hell is that?"

Chuck Bryant: Exactly. How hot is that one, Josh?

Josh Clark: It's two million degrees Kelvin, actually. Again, that is very hot.

Chuck Bryant: So it's not actually cooling as it goes outward. I completely misspoke.

Josh Clark: That's I think one of the reasons why the sun has these different features, like sun spots and solar prominences, which we're about to talk about. It's because these cooling and heating, and rising and lowering convection cells are kind of competing with one another. They actually create the magnetism that the plasma responds to.

Chuck Bryant: I don't feel too bad because the article says no one knows why the corona is so hot, because you'd think it would be cooler.

Josh Clark: Right.

Chuck Bryant: And there are hotter places than others because the cool spots are called coronal holes.

Josh Clark: Let's talk about sunspots, Chuck. Sunspots are these areas of magnetic activity along the photosphere, right?

Chuck Bryant: Darker and cooler.

Josh Clark: Right. They always appear in pairs, as far as I know, although I think they can appear singularly, though it's very uncommon because it's a monopole. Like I said, there's that convection activity. That actually creates the fields around the sun, right?

Chuck Bryant: Right.

Josh Clark: So when sunspots appear, generally they appear in pairs because one represents magnetic north and the other represents magnetic south. Along these magnetic fields, other solar activity can occur. You've got solar prominences, which is actually an arc of particles and radiation that can extend 1,000 kilometers outside of the sun's atmosphere. Right?

Chuck Bryant: Yeah. They last for two or three months. It's like a temporary thing.

Josh Clark: It's kind of like an arc of electricity, except a lot bigger.

Chuck Bryant: Right.

Josh Clark: Every once in a while, they erupt into coronal mass ejections.

Chuck Bryant: Right. Which is my next band name: Coronal Mass Ejection.

Josh Clark: That's a good one.

Chuck Bryant: I've got one more think on sunspots, which I thought was really cool. You know, they break through their magnetic fields. They break through the surface, but they only can exit and reenter though to the sunspots, which I thought was pretty cool.

Josh Clark: That is pretty cool. They also occur on 11-year cycles.

Chuck Bryant: Yes, the solar cycle.

Josh Clark: A full cycle, a full solar cycle is 22 years, so every 11 years it either peaks or troughs. What's interesting is, you know 2012? Everybody's like, "Oh, 2012, the world's going to end." I think we mentioned this in our 2012 podcast. That is the predicted peak of this solar cycle maximum that we're in. So you've got these sunspots. Sunspot activity is going to pick up. When sunspots pick up, solar prominences pick up. When there's more solar prominences, there's more coronal mass ejections. When there's more coronal mass ejections, the earth is inundated with radiation and radioactive particles, right?

Chuck Bryant: Right.

Josh Clark: They hit the earth's atmosphere and actually mess with the magnetic field. This actually accounts for the aurora borealis and australis, right?

Chuck Bryant: Right.

Josh Clark: And when enough of them hit the earth's atmosphere and they ionize, they interfere with our electrical activity.

Chuck Bryant: Right. They cause blackouts.

Josh Clark: Right, which is why a lot of people think 2012 will have all these catastrophes.

Chuck Bryant: That makes sense.

Josh Clark: But really it's just part of a 22-yer cycle of the sun.

Chuck Bryant: So calm down all you minds.

Josh Clark: Exactly. No, the minds don't think that.

Chuck Bryant: That's right. Josh, do you want to talk about the color of the sun real quick? This is a cool little fact that I bet most people don't know. Most people say the sun is yellow or orange. Not true. The sun is actually white. Sunlight is actually white. Do you know why it changes?

Josh Clark: Why?

Chuck Bryant: The atmosphere. The atmosphere acts as a filter for the setting sun. That's when it changes its color.

Josh Clark: It is white. It doesn't appear white, but it's actually made up of all the colors of the spectrum, which is why you can take a prism and shoot sunlight through it, and it spreads the different colors, and you have Pink Floyd's "Dark Side of the Moon" album cover.

Chuck Bryant: Right. I've got a couple of other cool facts.

Josh Clark: What?

Chuck Bryant: Rotation of the sun. Everyone knows it makes a complete rotation in about a month. But because it's a gas, basically, different parts rotate at different rates. Gas near the equator takes 25 days to rotate, and gas at higher latitudes may take as many as three more extra days. Pretty cool! So it's rotating at different rates.

Josh Clark: It is, because it's a ball of gas.

Chuck Bryant: Exactly. I've got one more. Are you ready for this one?

Josh Clark: Sure.

Chuck Bryant: About the vibration.

Josh Clark: Yeah, this is pretty cool, too, I thought.

Chuck Bryant: I had no idea. The sun vibrates constantly like a bell that's continuously struck.

Josh Clark: Right. Creating sound waves! But there's two minutes between intervals.

Chuck Bryant: Yes, and ten million individual tones at the same time. Crazy!

Josh Clark: Right, so we could, if our hearing was different - I don't know if better's the right word - but if we had a different type of hearing; we would be able to hear the vibrations coming off the sun. They actually do hit the earth, like I said, in two-minute intervals. The slowest distance between intervals, time wise, that humans can hear is one-twentieth of a second, so it's constantly making a sound. We just can't hear it. That leads me to the question.

Chuck Bryant: Uh oh.

Josh Clark: If the sun makes a sound while it's vibrating, can you hear it?

Chuck Bryant: I bet those blue people in "Avatar" can hear it. No? You still haven't seen it?

Josh Clark: I'll never see that movie.

Chuck Bryant: You should.

Josh Clark: Never.

Chuck Bryant: You're going to be that guy?

Josh Clark: Yeah.

Chuck Bryant: Okay. That's fine. I got a couple of other stats for you, if you're into it.

Josh Clark: Why not?

Chuck Bryant: Fewer than five percent of the stars in the Milky Way are brighter or more massive than the sun, but some are more than 100,000 times as bright. Isn't that crazy?

Josh Clark: Yes. That is pretty cool, actually.

Chuck Bryant: If you're going the other way, some stars are less than one-ten-thousandth as bright as the sun.

Josh Clark: Which is kind of nuts, but really, stat-wise, we have a fairly mediocre sun.

Chuck Bryant: Yes, but it does the trick though.

Josh Clark: It does do the trick, and it should for about the next five billion years, like we said.

Chuck Bryant: Yes. The sun is middle-aged right now. It's about halfway through.

Josh Clark: It's starting to look into wearing track suits all the time.

Chuck Bryant: Right.

Josh Clark: Out in public. After about five billion years, it's going to run out of fuel.

Chuck Bryant: Yeah, run out of hydrogen. What happens then?

Josh Clark: The density of the core is going to remain, but it's not going to have the fuel to create these nuclear reactions. Remember, we said the sun is a bunch of nuclear reactions, gravity smashing things together, and then the energy escaping. It's this constant push and pull. When it runs out of fuel, there's going to be nothing but pull. There won't be any push any longer, right?

Chuck Bryant: Right. Which is bad news for the core?

Josh Clark: Right. Before this happens, when this kicks off, it's going to turn into a -

Chuck Bryant: Red giant.

Josh Clark: Right. And this red giant, you know how the sun just kind of heats the earth?

Chuck Bryant: Yes.

Josh Clark: Well, that's not going to happen. I mean, it'll heat the earth, but it's also going to vaporize it when it turns into a red giant.

Chuck Bryant: Exactly, which is the bad news for us?

Josh Clark: We probably won't be around. We'll be long gone. There'll be no trace of humanity anywhere.

Chuck Bryant: In five billion years?

Josh Clark: No way.

Chuck Bryant: I would think not.

Josh Clark: I don't know that we have that much staying power.

Chuck Bryant: No.

Josh Clark: So the sun is going to vaporize the earth, which will probably be pretty wicked-cool to see when that does happen. After that, the core will turn into carbon. I misspoke earlier.

Chuck Bryant: Right, which cools it down!

Josh Clark: Right. As it cools, it'll turn into a white dwarf, and then a black dwarf.

Chuck Bryant: Eventually, yes.

Josh Clark: Then it'll just be some hulk that won't even resemble our sun anymore.

Chuck Bryant: Right, and once this whole process starts, it's going to take several billion years to complete that process. It's not like it happens overnight or anything.

Josh Clark: Probably about ten billion years from now, the sun will be just this massive hulk of carbon.

Chuck Bryant: Right. Like my brain is right now. Not so massive though.

Josh Clark: Can we be done now?

Chuck Bryant: I think so. There's a lot more. We didn't even touch on solar wind and things like that, but we leave it up to the listener to pursue these.

Josh Clark: Do we?

Chuck Bryant: Sure.

Josh Clark: The listener or Stuff From the Science Lab, our soon-to-be-forthcoming sister podcast with the esteemed Robert Lamb, and his esteemed editor Allison Loudermilk.

Chuck Bryant: Then we can just talk about noodling.

Josh Clark: Yeah. We'll go back to what we do best, which is bumpkin stuff. Chuck, I can barely get it out. Listener mail.

Chuck Bryant: Okay. I feel so defeated. I'm just going to call this, "The Best Part of This Podcast." This is on human experimentation. As always, if we put out a call for some random weirdness, there's someone out there who listens to the show who's been there and done that.

Josh Clark: Yeah. Remember the kid whose father used him as a human shield when he was a baby?

Chuck Bryant: I know. Remarkable! So I've got this one from Rebecca. She says this. "I just listened to the podcast on human experimentation. I was thrilled that you featured something I can relate to because I'm a former NASA human test subject."

Josh Clark: We just talked about NASA!

Chuck Bryant: I know.

Josh Clark: Weird.

Chuck Bryant: Funny how that works. "In 2006, I spent three months in a bed at a negative-six-degree tilt." Isn't that crazy? The effects of the human body at that angle are very similar to what an astronaut goes through after spending extended periods of time in space," which makes me wonder how they figured that out. Because they're NASA! That's the answer.

Josh Clark: Yeah.

Chuck Bryant: "Eventually, NASA hopes to take that information they got from my time in bed to help astronauts stay in space longer and travel further from the earth, and one day even land on Mars. As a test subject, everything I did, from surfing the internet, eating, reading, even using the bathroom, was at an angle, at a six-degree tilt. "Five days a week, I was wheeled to a lab where I was attached to an elaborate pulley system that pulled me onto a treadmill that was bolted to the wall. I walked, jogged, and ran a few miles a day to help my body avoid muscle atrophy." Of course! "Not everyone selected for the study was so lucky, though. Half of them did not get to run on this unique contraption." They were just in bed the whole time. "The data the engineers got from my running will help NASA figure out what types of exercise astronauts will have to do to experience long extended trips into space. While I didn't love everything about it - going to the restroom, for example - it was a thrilling thing to have been a part of. I'm a huge fan, and I like to learn neat stuff. Rebecca."

Josh Clark: Did you add that last part?

Chuck Bryant: No, she said that.

Josh Clark: Okay.

Chuck Bryant: Yeah. More neat stuff!

Josh Clark: Thanks, Rebecca. Hats off to you for helping our astronauts!

Chuck Bryant: She didn't mention how much she got paid, if at all, but I imagine she did.

Josh Clark: NASA has deep pockets, buddy.

Chuck Bryant: That's what I hear.

Josh Clark: Well, if you have any stories about developing bed sores for the great er good of advancing human knowledge, you can send it in an email to

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