Week 4: Anatomy of the Sun

As (most) people know, the Sun is a star. Since it's relatively very close to us, it's the most well-studied star by far. In fact, our class is studying the Sun (specifically its size, rotational speed, and period) in our lab this semester. It's about 8 light-minutes from the Earth, has a mass over 300,000 times that of the Earth, and a surface temperature around 5,800K. However, the Sun is more than just a ginormous blob of plasma--we wouldn't be around without the Sun, so let's try to show some respect. Instead, the Sun actually has a fairly well-defined structure:

Like the Earth, the Sun has a core. Like the Earth, the Sun's core is hotter than its surface. Unlike the Earth, the Sun's core is about 15 million degrees Kelvin. Most of the heat of the Sun comes from the core, which extends to about 25% of the solar radius (this gives it about 30 times the radius of the Earth, for comparison). This heat is produced by the fusion of hydrogen nuclei into helium nuclei, which releases a small amount of energy for each reaction, but these reactions add up--almost 10³⁹ of these reactions occur each second.

The next layer is the radiative zone, in which energy is transferred via radiation. It takes a long time for radiation to pass through this layer--gamma rays take over 170,000 years to make the trip from the core to the Sun's next layer. This is because any radiation that is emitted is quickly absorbed and re-emitted by the particles in this region, so there's no way of taking anything remotely resembling a direct path out of the core.

Next is the convection zone, where convection is the main form of energy transport. The convection zone and the radiative zone rotate slightly differently from one another, resulting in a dividing layer between the two known as the tachocline. This allows hot plasma to rise away from the Sun's center and cool ("cool" being ~5800K) plasma to sink back towards the core, thus creating currents and transporting heat and energy towards the surface.

Finally, the surface of the Sun--known as the photosphere--is where energy can finally be released into space and towards everyone trying to get a tan here on Earth. Interestingly, the photosphere, which is mostly composed of atomic hydrogen, is actually more transparent than the air on Earth. The surface and atmosphere of the Sun have their own features. These include the heliosphere, which is full of solar wind, and the corona, which for unknown reasons can reach temperatures up to 20 million Kelvin--a number that definitely puts my complaints about 80˚F temperatures in the summer in perspective.

Sources
https://en.wikipedia.org/wiki/Sun
https://ase.tufts.edu/cosmos/pictures/stars/Fig5_5Anatomy_of_the_Sun.jpg
https://en.wikipedia.org/wiki/Earth
https://en.wikipedia.org/wiki/Radiation_zone
https://en.wikipedia.org/wiki/Convection_zone
https://imgs.xkcd.com/comics/the_sun.png