1. © 2010 Pearson Education, Inc. The Sun

2. © 2010 Pearson Education, Inc. Why was the Sun’s energy source a major mystery?

3. © 2010 Pearson Education, Inc. Is it on FIRE?

4. © 2010 Pearson Education, Inc. Is it on FIRE? Luminosity ~ 10,000 years Chemical energy content

5. © 2010 Pearson Education, Inc. Is it on FIRE? … NO! Luminosity ~ 10,000 years Chemical energy content

6. © 2010 Pearson Education, Inc. Is it CONTRACTING? Insert TCP 6e Chapter 14 opener

7. © 2010 Pearson Education, Inc. Is it CONTRACTING? Luminosity Gravitational potential energy ~ 25 million years

8. © 2010 Pearson Education, Inc. Is it CONTRACTING? … NO! Luminosity ~ 10,000 years Chemical energy content

9. © 2010 Pearson Education, Inc. Why does the Sun shine?

10. © 2010 Pearson Education, Inc. It can be powered by NUCLEAR ENERGY! (E = mc 2 ) Luminosity ~ 10 billion years Nuclear potential energy (core)

11. © 2010 Pearson Education, Inc. Weight of upper layers compresses lower layers. Insert TCP 6e Figure 14.1

12. © 2010 Pearson Education, Inc. Gravitational equilibrium: Energy supplied by fusion maintains the pressure that balances the inward crush of gravity.

13. © 2010 Pearson Education, Inc. Gravitational contraction: Provided the energy that heated the core as Sun was forming Contraction stopped when fusion began.

14. © 2010 Pearson Education, Inc. Radius: 6.9  10 8 m (109 times Earth) Mass: 2  10 30 kg (300,000 Earths) Luminosity: 3.8  10 26 watts

15. © 2010 Pearson Education, Inc. What is the Sun’s structure? Insert TCP 6e Figure 14.3

16. © 2010 Pearson Education, Inc. Solar wind: A flow of charged particles from the surface of the Sun

17. © 2010 Pearson Education, Inc. Corona: Outermost layer of solar atmosphere ~1 million K

18. © 2010 Pearson Education, Inc. Chromosphere: Middle layer of solar atmosphere ~ 10 4 –10 5 K

19. © 2010 Pearson Education, Inc. Photosphere: Visible surface of Sun ~ 6000 K

20. © 2010 Pearson Education, Inc. Convection Zone: Energy transported upward by rising hot gas

21. © 2010 Pearson Education, Inc. Radiation Zone: Energy transported upward by photons

22. © 2010 Pearson Education, Inc. Core: Energy generated by nuclear fusion ~ 15 million K

23. © 2010 Pearson Education, Inc. How does nuclear fusion occur in the Sun?

24. © 2010 Pearson Education, Inc. Fission Big nucleus splits into smaller pieces. (Example: nuclear power plants) Fusion Small nuclei stick together to make a bigger one. (Example: the Sun, stars)

25. © 2010 Pearson Education, Inc. High temperatures enable nuclear fusion to happen in the core.

26. © 2010 Pearson Education, Inc. The Sun releases energy by fusing four hydrogen nuclei into one helium nucleus.

27. © 2010 Pearson Education, Inc. The proton–proton chain is how hydrogen fuses into helium in Sun.

28. © 2010 Pearson Education, Inc. IN 4 protons OUT 4 He nucleus 2 gamma rays 2 positrons 2 neutrinos Total mass is 0.7% lower.

29. © 2010 Pearson Education, Inc. Convection (rising hot gas) takes energy to surface.

30. © 2010 Pearson Education, Inc. Bright blobs on photosphere show where hot gas is reaching the surface.

31. © 2010 Pearson Education, Inc. Neutrinos created during fusion fly directly through the Sun. Observations of these solar neutrinos can tell us what’s happening in core.

32. © 2010 Pearson Education, Inc. Solar neutrino problem: Early searches for solar neutrinos failed to find the predicted number. More recent observations find the right number of neutrinos, but some have changed form.

33. © 2010 Pearson Education, Inc. What causes solar activity?

34. © 2010 Pearson Education, Inc. Solar activity is like “weather”. Sunspots Solar flares Solar prominences All these phenomena are related to magnetic fields.

35. © 2010 Pearson Education, Inc. Sunspots Are cooler than other parts of the Sun’s surface (4000 K) Are regions with strong magnetic fields

36. © 2010 Pearson Education, Inc. Zeeman Effect We can measure magnetic fields in sunspots by observing the splitting of spectral lines.

37. © 2010 Pearson Education, Inc. Loops of bright gas often connect sunspot pairs.

38. © 2010 Pearson Education, Inc. Magnetic activity causes solar flares that send bursts of X rays and charged particles into space.

39. © 2010 Pearson Education, Inc. Magnetic activity also causes solar prominences that erupt high above the Sun’s surface.

40. © 2010 Pearson Education, Inc. Charged particles streaming from the Sun can disrupt electrical power grids and can disable communications satellites.

41. © 2010 Pearson Education, Inc. How does solar activity vary with time?

42. © 2010 Pearson Education, Inc. The number of sunspots rises and falls in an 11-year cycle. Insert TCP 6e Figure 14.21a unannotated Insert TCP 6e Figure 14.21b unannotated

43. © 2010 Pearson Education, Inc. The sunspot cycle has something to do with winding and twisting of the Sun’s magnetic field.