1. Chapter 10 Our Star

2. 10.1 A Closer Look at the Sun Our Goals for Learning Why does the Sun shine? What is the Sun’s structure?

3. Why does the Sun shine?

4. Is it on FIRE?

5. Luminosity ~ 10,000 years Chemical Energy Content

6. Is it on FIRE? … NO! Luminosity ~ 10,000 years Chemical Energy Content

7. Is it CONTRACTING?

8. Luminosity Gravitational Potential Energy Is it CONTRACTING? ~ 25 million years

9. Luminosity Gravitational Potential Energy Is it CONTRACTING? … NO! ~ 25 million years

10. Luminosity ~ 25 million years Gravitational Potential Energy Is it CONTRACTING? … NO! E = mc 2 - Einstein, 1905

11. Is it powered by NUCLEAR ENERGY? Luminosity ~ 10 billion years Nuclear Potential Energy (core)

12. Is it powered by NUCLEAR ENERGY? … YES! Luminosity ~ 10 billion years Nuclear Potential Energy (core)

13. Gravitational equilibrium: The outward push of pressure balances the inward pull of gravity

14. Weight of upper layers compresses lower layers

15. Gravitational equilibrium: Energy provided by fusion maintains the pressure

16. Gravitational contraction: Provided energy that heated core as Sun was forming Contraction stopped when fusion began

17. What is the Sun’s structure?

18. Radius: 6.9 x 10 8 m (109 times Earth) Mass: 2 x 10 30 kg (300,000 Earths) Luminosity: 3.8 x 10 26 watts

19. Solar wind: A flow of charged particles from the surface of the Sun

20. Corona: Outermost layer of solar atmosphere ~1 million K

21. Chromosphere: Middle layer of solar atmosphere ~ 10 4 - 10 5 K

22. Photosphere: Visible surface of Sun ~ 6,000 K

23. Convection Zone: Energy transported upward by rising hot gas

24. Radiation Zone: Energy transported upward by photons

25. Core: Energy generated by nuclear fusion ~ 15 million K

26. Why does the Sun shine? The Sun shines because gravitational equilibrium keeps its core hot and dense enough to release energy through nuclear fusion. What have we learned?

27. What is the Sun’s structure?

28. 10.2 Nuclear Fusion in the Sun Our Goals for Learning How does nuclear fusion occur in the Sun? How does the energy from fusion get out of the Sun? How do we know what is happening inside the Sun?

29. How does nuclear fusion occur in the Sun?

30. Fission Big nucleus splits into smaller pieces (Nuclear power plants) Fusion Small nuclei stick together to make a bigger one (Sun, stars)

31. High temperature enables nuclear fusion to happen in the core

32. Sun releases energy by fusing four hydrogen nuclei into one helium nucleus

33. Proton-proton chain is how hydrogen fuses into helium in Sun

34. IN 4 protons OUT 4 He nucleus 2 gamma rays 2 positrons 2 neutrinos Total mass is 0.7% lower

35. Thought Question What would happen inside the Sun if a slight rise in core temperature led to a rapid rise in fusion energy? A. The core would expand and heat up slightly B. The core would expand and cool C. The Sun would blow up like a hydrogen bomb

36. Thought Question What would happen inside the Sun if a slight rise in core temperature led to a rapid rise in fusion energy? A. The core would expand and heat up slightly B. The core would expand and cool C. The Sun would blow up like a hydrogen bomb Solar thermostat keeps burning rate steady

37. Solar Thermostat Temperature Restored Temperature Decreases Fusion Rate Decreases Core compresses

38. Solar Thermostat Temperature Restored Temperature Increases Fusion Rate Increases Core expands

39. How does the energy from fusion get out of the Sun?

40. Energy gradually leaks out of radiation zone in form of randomly bouncing photons

41. Convection (rising hot gas) takes energy to surface

42. Bright blobs on photosphere are where hot gas is reaching surface

43. Patterns of vibration on surface tell us about what Sun is like inside Results agree very well with mathematical models of solar interior

44. 10.3 The Sun-Earth Connection Our Goals for Learning What causes solar activity? How does solar activity affect humans? How does solar activity vary with time?

45. What is solar activity?

46. Solar activity is like “weather” Sunspots Solar Flares Solar Prominences All related to magnetic fields

47. Sunspots Are cooler than other parts of the Sun’s surface (4000 K) Are regions with strong magnetic fields

48. Charged particles spiral along magnetic field lines

49. Loops of bright gas often connect sunspot pairs

50. Loops trace magnetic field lines

51. Solar flares- Bursts of X- rays and charged particles Caused by Magnetic activity

52. Corona appears bright in X-ray photos in places where magnetic fields trap hot gas

53. How does solar activity affect humans?

54. Coronal mass ejections send bursts of energetic charged particles out through the solar system

55. Charged particles streaming from Sun can disrupt electrical power grid and can disable communications satellites

56. Northern Lights (aurora)- Energetic particles high in Earth’s atmosphere

57. How does solar activity vary with time?

58. Number of sunspots rises and falls in 11-year cycle

59. Sunspot cycle has something to do with winding and twisting of Sun’s magnetic field

60. What have we learned? What causes solar activity? Convection combined with the rotation pattern of the Sun—faster at the equator than at the poles—causes solar activity because these gas motions stretch and twist the Sun’s magnetic field.

61. What have we learned? How does solar activity affect humans? Bursts of charged particles ejected from the Sun during periods of high solar activity can hamper radio communications,disrupt electrical power generation,and damage orbiting satellites.

62. What have we learned? How does solar activity vary with time? The sunspot cycle, or the variation in the number of sunspots on the Sun’s surface,has an average period of 11 years.The magnetic field flip-flops every 11 years or so, resulting in a 22-year magnetic cycle.