1. Chapter 14 Our Star http://en.wikipedia.org/wiki/Sun

2. 14.1 A Closer Look at the Sun Our goals for learning How was the Sun ’ s energy source a major mystery? How does the Sun shine? What is the Sun ’ s structure?

3. How come the Sun ’ s energy source a major mystery?

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. How does the Sun shine?

11. It can be powered by NUCLEAR ENERGY! http://en.wikipedia.org/wiki/Nuclear_Energy http://en.wikipedia.org/wiki/Nuclear_Energy Luminosity ~ 10 billion years Nuclear Potential Energy (core) E = mc 2 - Einstein, 1905

12. Weight of upper layers compresses lower layers

13. Gravitational equilibrium: Energy provided by fusion maintains the pressure http://en.wikipedi a.org/wiki/Nucle ar_fusion

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

15. What is the Sun ’ s structure?

16. 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

17. Solar wind: A flow of charged particles from the surface of the Sun http://en.wikipe dia.org/wiki/So lar_wind

18. Corona: Outermost layer of solar atmosphere ~1 million K http://en.wikipe dia.org/wiki/Co rona

19. Chromosphere: Middle layer of solar atmosphere ~ 10 4 - 10 5 K http://en.wikipedia. org/wiki/Chromosp here

20. Photosphere: Visible surface of Sun ~ 6,000 K http://en.wikipedi a.org/wiki/Photos phere

21. Convection Zone: Energy transported upward by rising hot gas http://en.wikipedia. org/wiki/Convectio n_zone

22. Radiation Zone: Energy transported upward by photons http://en.wikipedia. org/wiki/Radiation _zone

23. Core: Energy generated by nuclear fusion ~ 15 million K http://en.wikipedia. org/wiki/Solar_cor e

24. What have we learned? Why was the Sun ’ s energy source a major mystery? –Chemical and gravitational energy sources could not explain how the Sun could sustain its luminosity for more than about 25 million years Why does the Sun shine? –The Sun shines because gravitational equilibrium keeps its core hot and dense enough to release energy through nuclear fusion. Stars are gravitationally control thermonuclear fusion reactors.

25. What have we learned? What is the Sun ’ s structure? –From inside out, the layers are: Core Radiation Zone Convection Zone Photosphere Chromosphere Corona

26. 14.2 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?

27. How does nuclear fusion occur in the Sun?

28. Fission http://en.wikipedia.org/ wiki/Nuclear_fission Big nucleus splits into smaller pieces (Nuclear power plants) Fusion http://en.wikipedia.org/ wiki/Nuclear_fusion Small nuclei stick together to make a bigger one (Sun, stars)

29. High temperature enables nuclear fusion to happen in the core Positively charge protons would repel each other as Benjamin Franklin taught us. Strong Nuclear Force http://en.wikipedia.o rg/wiki/Strong_force QCD, Quantum Chromo Dynamics http://en.wikipedia.org/wiki /Quantum_chromodynamic s

30. Sun releases energy by fusing four hydrogen nuclei into one helium nucleus Net Results

31. Proton-proton chain is how hydrogen fuses into helium in Sun http://en.wikipedia.org/wiki/Proton-proton_reaction

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

33. 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

34. 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

35. Solar Thermostat Decline in core temperature causes fusion rate to drop, so core contracts and heats up Rise in core temperature causes fusion rate to rise, so core expands and cools down

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

37. Energy gradually leaks out of radiation zone in form of randomly bouncing photons Photon Diffusion: http://en.wikipedia.org/wiki/Photon_diffusion http://en.wikipedia.org/wiki/Photon_diffusion

38. Convection (rising hot gas) takes energy to surface http://en.wikipedia.org/wiki/Convection

39. Bright blobs on photosphere are where hot gas is reaching surface Granular Solar Physics http://en.wikipedia.org/wiki/Granule_%28solar_physics%29

40. How we know what is happening inside the Sun?

41. We learn about inside of Sun by … Making mathematical models Observing solar vibrations Observing solar neutrinos http://en.wikipedia.org/wiki/Solar_neutrinos http://en.wikipedia.org/wiki/Solar_neutrinos

42. Patterns of vibration on surface tell us about what Sun is like inside http://gong.nso.ed u/infohttp://gong.nso.ed u/info GONG, Global Oscillation Network Group

43. Data on solar vibrations agree very well with mathematical models of solar interior

44. Neutrinos created during fusion fly directly through the Sun The Sun is transparent to neutrinos. Observations of these solar neutrinos can tell us what ’ s happening in core

45. Solar neutrino problem: Early searches for solar neutrinos failed to find the predicted number. Down by a factor of three. This experiment was done deep underground only neutrinos could penetrate that far. Cl was transformed to Ar when a neutron was transformed into a proton and an electron by the absorption of a neutrino. http://en.wikipedia.org/wiki/Solar _neutrino_problem

46. 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 Neutrino Oscillations: http://en.wikipedia.org/wi ki/Neutrino_oscillation Neutrinos http://en.wikipedia.org/wi ki/Neutrino

47. What have we learned? How does nuclear fusion occur in the Sun? –The core ’ s extreme temperature and density are just right for nuclear fusion of hydrogen to helium through the proton-proton chain –Gravitational equilibrium acts as a thermostat to regulate the core temperature because fusion rate is very sensitive to temperature

48. What have we learned? How does the energy from fusion get out of the Sun? –Randomly bouncing photons carry it through the radiation zone –Rising of hot plasma carries energy through the convection zone to photosphere How do we know what is happening inside the Sun? –Mathematical models agree with observations of solar vibrations and solar neutrinos

49. 14.3 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?

50. What causes solar activity? http://en.wikipedia.org/wiki/Solar_activity http://en.wikipedia.org/wiki/Solar_activity

51. Solar activity is like “ weather ” Sunspots http://en.wikipedia.org/wiki/Sunspotshttp://en.wikipedia.org/wiki/Sunspots Solar Flares http://en.wikipedia.org/wiki/Solar_flares http://en.wikipedia.org/wiki/Solar_flares Solar Prominences http://en.wikipedia.org/wiki/Solar_Prominence http://en.wikipedia.org/wiki/Solar_Prominence All are related to magnetic fields http://en.wikipedia.org/wiki/Magnetic_field http://en.wikipedia.org/wiki/Magnetic_field

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

53. Zeeman Effect We can measure magnetic fields in sunspots by observing the splitting of spectral lines http://en.wik ipedia.org/w iki/Zeeman_ effect

54. Charged particles spiral along magnetic field lines

55. Loops of bright gas often connect sunspot pairs

56. Magnetic activity causes solar flares that send bursts of X-rays and charged particles into space

57. Magnetic activity also causes solar prominences that erupt high above the Sun ’ s surface

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

59. How does solar activity affect humans?

60. Coronal mass ejections send bursts of energetic charged particles out through the solar system http://en.wikipedia.org/wiki/Coronal _mass_ejection

61. Charged particles streaming from Sun can disrupt electrical power grids and can disable communications satellites

62. How does solar activity vary with time?

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

64. Sunspot cycle has something to do with winding and twisting of Sun ’ s magnetic field Babcock Model: http://en.wikipedia.org/wiki/Babcock_Model http://en.wikipedia.org/wiki/Babcock_Model

65. What have we learned? What causes solar activity? –Stretching and twisting of magnetic field lines near the Sun ’ s surface causes solar activity How does solar activity affect humans? –Bursts of charged particles from the Sun can disrupt communications, satellites, and electrical power generation How does solar activity vary with time? –Activity rises and falls with an 11-year period