In this paper I want to describe how the sun works. I will also comment about its properties and how it affects us here on Earth with its radiation. Our Sun is a star and is the closest one to us by far. That gives us the opportunity to study it more closely than any other star.
How The Sun Works
I want to start out by saying that our Sun is our only source of heat. Without it, our planet Earth would freeze and us along with it. We would not survive. That is how important this star is to our survival. So what is a star? It is a sphere of extremely hot gas. Strong gravity is what helps the Sun hold its shape and keep all this gas in one place. In the center of the Sun are constant nuclear reactions that keep the engine turning.
Properties Of The Sun
The Sun is quite large by our standards. It's radius was measured to be almost 700,000 kilometers and diameter to be 1,400,000 km. This measurement was made by the SOHO spacecraft a few years ago. It also rotates just like us here. Rotation is different though according to the location on the Sun. It is faster at the equator than towards its poles. This is called differential rotation. Since its rotation is differential, we can infer that the Sun is not solid and is instead gaseous and fluid. Complete rotation takes about a month. The temperature is pretty hot at around an average 5800 kelvin.
The Suns's radiation reaches us here on Earth. Its energy is what gives us warmth and allows us to live. Different amounts reach here depending on the location. The equator gets more than our poles. That is because the equator faces the Sun more. Earth is tilted after all. The poles get very little radiation and is why they are so much colder.
Layout Of The Sun
The layout of our star has been quite organized by those studying it. It is divided into several regions. Those regions are the photosphere, chromosphere, transition zone, corona, convection zone, radiation zone and its central core. These zones all serve different functions. Studying them will explain how the Sun works and allow greater understanding of our universe.
The photosphere is what we see when looking toward the Sun. It is also where most of the light comes from. It takes 8 minutes for the Sun's light to reach us here on Earth and it constantly bombards us.
Brightness Of The Sun
We know that the Sun gives off a lot of radiation. How do we know that? Look at the light during the daytime. Light is the Sun's radiation. Most people do not think about that. We can measure this light as well. There is a solar constant which is the amount of light that hits a given spot of a certain size. At first we thought this was very constant. That is reported anyway. I do not believe it is that constant all the time and that it can vary a lot. When it gets very cold or hotter than normal for a period of years, this is the Sun being variable. This has happened throughout recorded history and is most likely what is happening instead of global warming due to mankind. A lot of the Sun's light does not even reach us. Only a tiny fraction gets through to us. That is important to realize when you consider our hot days during the summer. Only a very tiny fraction comes through space and past our atmosphere.
Standard Solar Model
Since we are not able to directly observe the interior of the Sun we have to make assumptions based off of things we do know. Putting all these assumptions together is called a model. So we have an information model of the Sun that we work from. It comes from a little direct observation and various laws of the universe that are already in place and accepted. Specifically these are the laws of energy, momentum, and mass. Now when physicists put all these things together they are assuming the Sun is a perfect sphere and radiates energy outwardly in an even fashion. The reason this is done is that is because non-uniformity increases the complexity of these problems immensely. Most actually think this is still pretty accurate as well.
As we talk about how the Sun works it is important to know about its hydrostatic equilibrium. What this means is that its pressure and gravitational forces are close to equal most of the time. This is actually one of the reasons we assume that its energy output is fairly equal in all directions. Most stars will also stay in equilibrium too. The reason for this is that these forces self-regulate. If one force gets increased by an external factor it can usually balance itself out. This is also one of the reasons why stars and objects like them can be so long-lasting.
Energy Transport Inside The Sun
Since the Sun is so hot near its core, collisions between particles happen continually. These collisions carry energy. Now we know that the temperature drops the further from the core that you get. This is important because electrons will stay with their atoms easier. Electrons carry energy in their excited states. You may see a problem by now. How does energy move to the surface and beyond then? The way it moves is by convection. This is how energy escapes the Sun and is very important as to how the Sun works.
When looking at pictures of the Sun's surface you will see many granulated regions. These are huge areas of intense heat. The granulated regions appear to be different colors. Color is mostly dependent on the temperature of individual cells.
Spectral Lines Of The Sun
Spectral lines appear when electrons change states. When doing tests we can use these lines to see the composition of what we are studying. Spectral lines of the Sun can tell us the elements that constitute it. However, these lines also give evidence that the temperature of the Sun decreases as you get away from the photosphere.
This is a region just above the photosphere. It is much dimmer and a little cooler than the photosphere also. The chromosphere spawns solar storms that sends out spicules into the atmosphere. It is approximately 4000 km deep. The temperature of the chromosphere is also unusual because its area around the photosphere is cooler than at the top of the chromosphere. Usually anything gets cooler the further from its core it gets. So this makes the chromosphere of the Sun quite unusual. Shockwaves from the photosphere move into the chromosphere at a high velocity. This helps in heating the surrounding areas.
The corona is a fascinating region of the Sun's atmosphere. Elements arising from this area are in much different forms than anywhere else. Coronal temperatures are much higher on average than the photosphere even. Temperatures of 3-15 million k are common here. That is extraordinary. Intuition says there must be something else causing the heat instead of just the core. It is not clear what this mechanism is though.
For all of its heat, it is not very bright. We normally see it during eclipses. Magnetic forces move energy into the corona. This produces its high temperatures. The corona constantly leaks into space with the solar wind carrying its particles far and in most directions at once.
The Sun's solar wind is not really a wind in the sense that we know it. It is more akin to a stream of radiation and particles that have been ejected at super high speeds. As far as we know radiation and particles are ejected outwardly in an even fashion. It all comes from the corona itself because the temperatures are so high there.
Magnetism is one of my favorite subjects. It is no less interesting or relative when talking about how the Sun works. Our Sun has a very strong magnetic field. Its mechanisms and insides follow the electromagnetic laws. Astronomers do not know where its magnetism is created though. Many are still studying this. If I was to guess I would say the magnetic forces are created constantly. The reason I say this is because the high temperatures separate molecules and atoms into individual particles. When these particles are then moved by the abundant energy all around them, they create magnetic fields. Since temperatures everywhere in the Sun are so hot this happens a lot. That is my take on it. I could be totally off but we will see.
Sunspots Within The Sun
Sunspots are dark patches that often appear on the Sun's surface. They are quite large, about the size of Earth actually. Sometimes they appear singularly but also in groups. They appear dark because their temperatures are lower than the area around them. When seen up close they have a darker core and a slightly lighter area around the core.
The sunspots are all on a cycle. Most people think its around 11 years but others think there could be even larger cycles. As we get more data on how the Sun works this will be more evident. What this all means is there are quiet periods and there are raucous times as well.
The Magnetic Field
Magnetic fields within sunspots are pretty strong. They are much stronger than here on Earth. Since they are so strong, they redirect convection currents. This is what makes the sunspots darker and cooler than surrounding cells. Magnetic fields always have a polarity as well. This means the direction in which the field runs. Currents and particles seem to follow the same direction as the field lines. Sunspots in the northern hemisphere have opposite field directions as those in the southern hemisphere.
Cycles Of The Sun
This is still in regards to sunspots but it is still key to understanding how the Sun works. Astronomers have been observing the Sun for hundreds of years. During this time there are a few things they have noticed and passed down to later generations. One of these is that solar sunspots are quite variable and prone to change. Sizes, shapes, and durations of sunspots all change constantly. Our Sun does have a long cycle in which sunspots are more common. It is 22 years. We can further break this down into two 11-year periods though. During each 11-year period the polarities reverse.
Solar flares are born of the chaos of changing magnetic fields. They produce incredible amounts of energy. Energy is visible in multiple frequencies so we can study them with x-ray and ultraviolet detectors. They are basically very powerful explosions that occur on the Sun's surface.
What Powers The Sun
Everyone knows the Sun gives off lots of energy. The thing is, it continually does this and has done so for a long time. It is common sense that there must be some renewable source of energy and this mechanism is very efficient. This mechanism is nuclear fusion. Nuclear fusions is when two nuclei are joined together. A third nuclei is then formed. However, this third nuclei is smaller than the two previous nuclei. When this happens energy is created because that missing mass has to go somewhere. This is Einstein's $$ E = mc^2 $$ law. It predicts the energy released when this happens. This is what is constantly happening in the Sun and is fundamental to how the Sun works.
Hopefully by now you understand some of the basics of our parent star. There are so many fascinating details to study I could not even include everything. There are also newer but untested ideas being presented constantly. It will be quite interesting indeed to see what ultimately develops. I hope that I have shown how the Sun works to a sufficient degree here. If you have any questions please comment below and I will answer. Have a great day!