How do we model the Sun?

Well, before we answer that question, you need to understand what it means. You've all made models when you were younger with plasticine, clay or lego, but what do we mean by `making a model of the Sun'? As you get older, the models get more complicated. In science, we try to describe as accurately as possible how things behave. We build models. We use physics, mathematics and computers to build models of the Sun, to try to explain what we have observed.

So, the answer to the question `How do we model the Sun' depends on which part of the Sun that we are talking about -

Here is a diagram of the Sun, showing its insides aswell as its atmosphere. In this section, we concentrate on how to model some of the strange phenomena seen on the Sun. Three different parts of the solar atmosphere are pointed out; the solar surface, photosphere, the chromosphere, and the corona.

When astronomers discovered that the temperature in the solar atmosphere rises rapidly as the distance from the solar surface increases, they were amazed. Observations have provided us with measurements of how the temperature changes as you go higher in the solar atmosphere. This is shown in the illustration below.

Until recently we did not understand why the outer part of the solar atmosphere (the corona) is so hot, but we now have several clues to help us discover what is happening.

• All energy from the sun is produced in the solar core - far below the solar atmosphere.
  The temperature in the centre of the Sun is around 16,000,000 degrees. We would naturally expect the temperature to decrease as the distance from the center of the Sun increases.

• The laws of physics suggest that energy from a gas of a given temperature cannot normally be used to heat another gas to a higher temperature.

Take the example of a radiator or fireplace in your house. At nightime, the room never gets hotter that the radiator or fire, and the further away you are the cooler it gets. Of course, in the daytime, the Sun may be shining in through the windows and giving extra warmth to the room.

The situation in the solar atmosphere should be very similar. However, the temperature does not continue to decrease with height! Somehow the corona is heated a lot and the natural question is therefore:

Below are some other questions that have helped us to follow the right track. Follow us and let's see how far we can go.......

• Where does the energy come from? (The theory of rice puddings).

• How does the energy get up into the corona? (The physics of balloons and rubberbands.)

• How is the energy released in the corona? (How to cut and paste a rubberband.)

• How can we model this heating using physics and computers?

We, Aaron and Klaus, hope that you have had some fun in this section and got some idea how mathematical models on computer can help us understand complicated problems.