2. The Sun

3. Abundance of Elements in the Sun Element% by Number% by Mass Hydrogen92.073.4 Helium 7.825.0 Carbon0.02 0.20 Nitrogen0.008 0.09 Oxygen0.06 0.8 Neon0.01 0.16 Magnesium0.003 0.06

4. Relative sizes Visible sphere of the Sun Earth

5. Structure of the Sun

6. What Makes the Sun to Shine?  Chemical  Would only provide the necessary energy for 3000 years  Gravitational Contraction  Proposed by Helmholtz and Kelvin - would power the Sun for a few hundred million years  By the early 1900’s geologists showed that the Earth is billions of years old.

7. Nuclear Energy

8. Fundamental Forces  Strong Nuclear  Holds the nucleus of the atom together  Electromagnetic  Responsible for all chemical reactions  Weak Nuclear  Governs radioactive decay  Gravity

9. Proton-proton chain Step 1 1 H + 1 H —> 2 H + e + + neutrino Step 2 2 H + 1 H —> 3 He + photon 2H2H e+e+ 3 He photon 4 He photon 1H1H 1H1H Step 3 3 He + 3 He —> 4 He + 1 H + 1 H +photon

10. Hydrogen Fusion  Net result  4H --> He + e + + + energy  Four protons are 0.7% more massive than one He E = mc 2

11. 1.6 km C 2 Cl 4 Neutrino Telescope Cosmic Rays Ar Argon Atom 100,000 gal. tank Gold Mine Ar

12. Solar Neutrino Problem

14. Animation

15. Energy Transport  Conduction: the transfer of heat in a solid by collisions between atoms and/or molecules.  Not applicable in stars  Radiation: the transfer of energy by electromagnetic waves. Inside the Sun and most stars, radiation is the principal means of heat transport.  Convection: the transfer of heat in a gas or liquid by means of the motion of the material.

16. McMath-Pierce Solar Telescope

19. Photosphere Big Bear Solar Observatory October 21, 2009

20. The Sharp Limb  Limit of resolution is one arcsec  700 km at 1 AU  Density falls very quickly in photosphere Opaque here Transparent here

21. Limb Darkening  Same 700 km penetration depth  Viewed at disk center, light originates deeper  Temperature falls with height in photosphere

22. Temperature of Photosphere Photosphere

23. Solar Spectrum

24. Granulation  Typically 1000 km across  Bright center, dark edge  Center moving out, edges moving in The Movie

25. Granulation  Convection Hot Cool Hot

26. Chromosphere  Observing strategies  During total eclipses

27. Chromosphere  Using spectroheliograph H H 

28. Chromosphere Supergranulation

29. Chromosphere CaII 

30. Spicules Movie

31. The Corona The quiet corona The active corona

32. X-ray emission The Movie

33. Solar Wind Distance from photosphere Velocity Average particle velocity Escape Velocity

34. The Corona is Hot  The Corona is hot!  X-ray emission  Lines of highly ionized iron FeX, FeXIV, FeXV Requires T  2,000,000 K  Coronal holes are the source of the Solar Wind

35. End of Section