1. The Sun SSL July 2006

2. Sun Needs Fuel

3. Hydrostatic Equilibrium Gravity and pressure must balance If not, unstable

4. Energy Generation Two methods –Gravitational energy –Conversion of mass to energy

5. Energy Transport Two methods –Radiation –Convection Sun does both

6. Gravitational Energy Takes energy to lift mass Releases energy when gas falls Shrinking body will release gravitational energy and heat up

7. Relativity Energy and matter are equivalent E = mc 2

8. Gravitational contraction Can release copious energy However, no evidence the Sun is shrinking Would only last a few thousand years

9. Nuclear Energy Very large amounts of energy released Not very efficient –Needs high densities –Needs high temperatures

10. Eddington Proposed nuclear reactions to fuel the Sun First successful models Two main chains –P-P chain –CNO cycle

11. P-P chain

12. CNO Chain C, N and O act as catalysts in reaction More complicated reactions also happen but not as important

13. Solar Structure

14. Sun at many energies

15. Probing the Sun Helioseismology –Apply same principles as studies of the Earth –Disturbances travel through gas of the Sun –Resonances tell of structure –Sun quakes

16. Solar Interior Core –Energy transport is through radiation Convective zone –Energy transport is through convection Photosphere –Energy transport is through radiation into space

17. Solar Exterior Chromosphere is hotter than photosphere –Magnetic fields probably involved Corona –Million degrees –X-ray bright –Seen during eclipses

18. Solar Activity 22 year magnetic cycle 11 year cycle of strength