1. What do we know about the Sun?
2. How do we use computers?
3. What the computer tells us.
4. Testing the model

What do we know about the Sun?

What do you know about the Sun?

1. See LIGHT.
   Sunlight HEATS the Earth.
   -> Sun emits energy
   Why?
   Because it is hot.
   What makes it hot?

2. Sun is GAS, mostly hydrogen and helium

3. Sun is STABLE, but DYNAMIC

4. Use light to explore the surface and atmosphere of the Sun
   • Granulation
     Bright and dark pattern produced by hot and cool gas at surface of the Sun.

     

   • Magnetic field

     

5. Use sound waves to explore interior of the Sun - helioseismology
   Sun vibrates like an organ pipe.
   • Oscillation sound (audio)

   • Vibrating surface (movie)

   • Wave paths

     

How do we use computers?

How do you use computers?

Can't bring Sun into laboratory to study it.

I use computers to make models that imitate the behavior of the Sun

Scientists look for persistent patterns in nature.
Especially important are the conservation laws of

1. Mass (amount of matter)
2. Momentum (motion)
3. Energy (ability to do work)

Conservation means don't create or destroy, only move around and change form.
Example: Conservation of blocks - can hide in closet, can throw out or in window, but total number of blocks is not changed.

Behavior of the Sun is determined by the 3 conservation laws which are described by mathematical equations.
I use computers to solve these equations for a small piece of the Sun (about the size of the Earth) near its surface.

Method: Divide the volume to be studied into small cells (like rubik's cube).

Each cell has certain amount of gas, moving at some speed in a certain direction, with some energy.
Equations describe how current state determines change with time.

Change = amount in - amount out + amount produced

What the computer tells us.

What makes the Sun hot?

Heat is produced in center by nuclear reactions. Heat travels from hot center to cool surface by radiation and convection.

What is convection?

Hot gas rises, carries heat up, cools. Cool gas descends, gets reheated.

What is solar convection?

Use computers to visualize results as pictures.

Convection is like a fountain.

Hot gas from interior of Sun rises and expands in order to conserve mass as it goes from the dense interior to the low density surface. Only a small fraction reaches the surface. Most turns back down in the interior.

Hot gas that reaches the surface radiates away its energy (to produce the light that heats the Earth). It cools, becomes dense, and is pulled down by gravity in thin, turbulent plumes.

movie

Testing the models

When make model must always test it. How?

Compare predictions of model with observations and other things you believe.
If doesn't agree, then either the model or the observations need to be modified.

1. Shock tubes
   

   When divider is removed a shock (sonic boom) forms.
   Plug numbers into equations describing each side and see what happens.

   

2. Granulation

   Intensity pattern and statistics.

   

3. Light absorbed by atoms in atmosphere of Sun (spectral lines)

   Intensity vs. Doppler shift.
   Depends on temperature and motion of atoms.

   

4. Solar oscillations

   Excitation rate vs. frequency.

   

Do models agaree with observations?

If not -> back to the drawing board.
Sometimes tell observers they need to look again.
Sometimes I have to tinker with the model.
Dialog between theorists and observers.