When you talk about space, the Sun tends to come up a lot. But even though we have talked about it a lot before we've never given you a proper tour of our closest star. Today, we're going to change that. 

We'd have a bit of a problem sending a probe to the center of the Sun. It would vaporize long before it got there, so it wouldn't get to see very much, but what if we sent the intrepid SciShow spaceship with it's invincible Patreon funded hull. Then we get to check out the sun up close, including the different processes going on all of it's layers. 

One of the first things we would notice about the sun is that it's huge and its a place of extremes. It contains 99% of all the matter in the solar system, and just about all of it is in the form of plasma - a kind of superheated gas where electrons are stripped away from their atoms. Even the coolest places on the Sun's surface are hot enough to melt every compound humans have ever found, created or even predicted. 

And the Sun is so big that if it were hollow, you could pack under a million Earth's inside of it, but it isn't hollow. All of that plasma is organized into layers starting with the core, which makes light and heat. And it's very hot in there, with temperatures that probably go up to 15 million Kelvin. Pressures are about 250 billion times what you'd find on Earth's surface, making the plasma eleven times denser than lead. At those temperatures and pressures, smaller atoms start combining into larger ones in a process known as nuclear fusion, which release a lot energy. It's how the sun, like every other star, shines.

The Sun produces about 420 million billion billion Watts of power every second. That's 750,000 times all the energy all of humanity uses in a whole year...produced every second! The energy's released in the form of light which flies away from the reaction in a random direction. But it doesn't just zoom straight out of the Sun from there. According to most estimates, it actually takes 200,000 years for the light from the core to reach the surface.

The Sun is only about four light-seconds across, so a photon of light should only take about four seconds to cross the entire thing - if it were an empty shell. But the center of the Sun is so dense that light can only travel for about a hundredth of a nanosecond before running into an atom. That's only about a centimeter - in a star 140 billion centimeters across. When the light hits an atom that atom adsorbs energy and releases some of it as more light, which goes off in another random direction for another hundredth of a nanosecond before it's absorbed and then the process started all over again. It's not a very efficient way to get somewhere, but eventually the light ends up at the edge of the core. Meanwhile, the energy absorbed by each atom makes it a little warmer.

Once it's out of the core, light enters the radiative zone, which starts around a third of the Sun's radius and keeps going until about two thirds of the radius. There, the light just keeps running into atoms and transferring energy to them. The light and heat radiate outwards from the core towards the edges of the Sun - hence the name. But only 1% of the Sun's fusion happens in the radiative zone because, by this point, the temperatures, pressures and densities are all way too low. By the time it gets to the end of the radiative zone, the plasma is about a tenth of the temperature and a hundredth of the density it was at the center of the core. Most of the rest of the Sun is taken up by the convective zone. 

At this point, instead of light mostly transferring energy directly to atoms and making heat that way, the light just kind of passes by, and atoms transfer heat to each other in a process called convection. It's the same way heat circulates in the convection oven you might have in your kitchen: hot stuff rises and cooler stuff falls. Temperatures continue to drop across the convective zone until we reach the photosphere, the main layer you'll see if you look at the Sun through a special solar telescope. 

The photosphere is about 5,700 Kelvin, which is still way too hot for a stroll, but practically freezing compared to the 15 million Kelvin we saw in the core. And just outside of that layer is one of the Sun's biggest mysteries - in the form of a few wispy layers known as the chromosphere and the corona, which can be millions or even tens of millions of Kelvin. That is way hotter than the photosphere - and researchers don't really know what's heating it. It seems to contradict both thermodynamics and basic common sense: something cold shouldn't be able to heat something warm. There are a few possible explanations - magnetic fields in the Sun might be dragging matter around and superheating it in the process - but scientists still aren't sure. 

Thanks for joining us on this trip in the SciShow Space-Ship, and thanks especially to our patrons on Patreon who help make this show - and that ship - possible. If you want to help us keep exploring the universe, just go to patreon.com/schishow to learn more. 

*End credits*