You may not think about the Sun all that often outside of the heat of summer, or recently getting a sun burn. I mean what is there to know? It’s the Sun- it’s hot, big, makes the daytime, do you need to know more? The Sun, despite its dominant position in our Solar System, is not very well understood.
So what is the Sun? It’s a massive ball of mostly Hydrogen, about a fifth Helium, and some trace amounts of heavier metals like Carbon and Iron. It’s core is undergoing nuclear fusion, fusing Hydrogen atoms into Helium atoms and releasing tremendous amounts of energy. This energy trickles up to the surface as photons bouncing between atoms in the roiling plasma until it reaches the surface where it blasts out in all directions as Sunshine. Plasma is a form of matter like solid, liquid, and gas that is defined as being energetic and ionized so electromagnetic forces dominate its behavior (as opposed to mechanical forces with solids, liquids, and gases). This process from core to surface can take 100,000 years, so the light we see from the Sun was formed long before written history.
Nuclear fusion only takes place in the core, and surrounding it are several layers which have different properties. Outside the core is the Radiative zone, where the plasma is too dense for individual atoms to move around, so all energy is transmitted via radiation. Outside of the Radiative zone is the Convective zone, where the density of the plasma is low enough that atoms can move around and transport energy by moving from hot to cold zones. Near the surface is the Photosphere and Chromosphere, where energy returns to its form as photons and high energy particles and escape the Sun.
The Sun is a fairly typical star, so knowing more about the Sun can reasonably be extended to similar stars. Our star is a G-type Main Sequence star. On the smaller side are Red Dwarves, and on the larger side are Giants and Super Giants. The size of a star dictates many aspects of its behavior. Small Red Dwarves are typically convective all the way through, so the fusing Hydrogen is continually mixed. This extends their lifetime to many dozens of billions of years. They are also by far the most numerous type of star in our galaxy. Our star is 4.6 billion years old and is expected to remain in a similar state for another 5 billion years. Giant stars have all kinds of different behavior including cores of inert Helium and fusing shells of Hydrogen, or even fusing cores of Helium. They burn their fuel much faster and only live several million years or less. They are more rare and explode often, spreading heavy metals all over the galaxy and producing planets like Earth.
Our Sun has a complex magnetic field that is changing all the time due to the movement of the plasma within the Sun. This magnetic field causes features on the surface such as sunspots and solar flares. Solar flares are filaments of solar material spinning around a magnetic field that moves and shifts, blasting solar material out into space. That material can escape the Sun and hit the Earth, causing a geomagnetic storm that can affect electronics on Earth.
Even though it’s the biggest thing in our solar system and it’s right there, there’s a lot we don’t know about the Sun. The Sun goes through roughly eleven year cycles, and a lot of work is put into predicting and estimating that cycle, but we don’t know enough to get it right- it’s like predicting weather here on Earth. We’ve launched missions to observe the Sun from different orbits and using different instrumentation. We’ve even launched missions into our own magnetosphere to understand its interaction with solar particles.
So just because it’s so obvious and constant, the Sun is actually an amazing and mysterious thing. So learn some more about the Sun, and don’t forget to use sunscreen!