Hank Green: So, I live in Montana and it's winter right now, and it's cold and in February I walk outside and it looks like this, and sometimes I just wish that I lived on Mercury. Yeah, that looks nice. [intro music] So, the Sun is awesome. Whatever it is you're doing right now, you're only able to do because of the Sun, because the Sun gives us its heat and its light, which makes photosynthesis happen, which makes all of the food that you eat. So you might as well know how it works. The Sun is nothing more than a giant massive nuclear explosion that just keeps on exploding and exploding and exploding. So, the Sun was formed about 4.5 billion years ago, the same way that all other stars formed. There was a bunch of gas in the universe, and some of the gas started clumping together because of gravity. The more that that gas clumped together, the more gas wanted to be there, and it clumped together so hard that eventually two atoms of hydrogen fused together into helium, producing a huge amount of energy, and that started off a chain reaction that became the power of our sun. So now, at its core, where all the real, interesting action happens, the temperature there's about 27 million degrees Fahrenheit [(15 million degrees Celsius)]. From there, it takes about 170,000 years for that energy to reach the surface of the Sun, and by that time, it's cooled to a balmy 10,000 degrees. Often you'll hear people say, "We're gonna make this as hot as the surface of the Sun!", and it's important to note, the surface of the Sun? Not that hot compared to 27 million degrees. Other examples of hydrogen fusion that you're probably familiar with that do not occur on the Sun include the Tsar Bomba, the most powerful nuclear weapon ever detonated. It was detonated in the Soviet Union in 1961, and the way that fusion bombs work is they actually have basically a bunch of fission bombs going off at one to create enough pressure to make the hydrogen atoms fuse. Just the fission bombs that made the Tsar Bomba go off was equivalent to 50 megatons of TNT. The amount of stuff that was fused in the Tsar Bomba was about that big. By contrast, the area of the Sun where fusion is happening is about the size of 240,000 Earths, so if the Sun were to blow up all at once, like the Tsar Bomba did, it would basically melt everybody's faces off from here to Alpha Centauri. So, the Sun and the Tsar Bomba are basically the same thing on different scales. The question is, why doesn't the Sun blow up all at once? Lucky for us, the Sun naturally controls its pressure and its temperature and its fusion rate in a kind of natural thermostat. Basically, when the enormous heat and the explosive energy in the core make make it expand, the core becomes less dense, which makes the fusion rate slow down, and then gravity pulls the core back in. Then it starts all over again, and that's just the way the Sun rolls. That's not to say that some stars don't blow their wad all at once, or at least a lot faster. Our sun happens to be a g-type star, which is a tasteful, middle-of-the-road kind of mass for a star. As it happens, the less mass a star has, the dimmer it is, the redder it is, and the longer lived it is. Dim red dwarf, for example, can take trillions of years to burn out, while one of those big, blue O-type stars can burn through its entire allowance of hydrogen in, like one million years. So our sun is doing pretty good. It looks like it's got another 4.5 billion years or so before it, you know, sputters out. Ah, good old Sun. I miss it. Thanks for watching and learning during this SciShow Dose. If you wanna have more of this, you can subscribe at youtube.com/scishow. What else is going on? Oh, yeah -- you can hook up with us on Facebook and Twitter if you have any questions or ideas, and of course down in the YouTube comments below. [outro music]