1. Copyright © 2012 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 Our Star – The Sun

2. Copyright © 2012 Pearson Education, Inc. The Sun Why does the Sun shine? What is the Sun’s structure? What is the 11-year solar cycle?

3. Copyright © 2012 Pearson Education, Inc. Why does the Sun shine?

4. Copyright © 2012 Pearson Education, Inc. Is it on FIRE?

5. Copyright © 2012 Pearson Education, Inc. Is it on FIRE? Luminosity ~ 10,000 years Chemical Energy Content

6. Copyright © 2012 Pearson Education, Inc. Is it on FIRE? … NO! Luminosity ~ 10,000 years Chemical Energy Content

7. Copyright © 2012 Pearson Education, Inc. Is it CONTRACTING?

8. Copyright © 2012 Pearson Education, Inc. Is it CONTRACTING? Luminosity Gravitational Potential Energy ~ 25 million years

9. Copyright © 2012 Pearson Education, Inc. Is it CONTRACTING? … NO! Luminosity Gravitational Potential Energy ~ 25 million years

10. Copyright © 2012 Pearson Education, Inc. ALL STARS are powered by NUCLEAR ENERGY! Luminosity ~ 10 billion years Nuclear Potential Energy (core) E = mc 2 —Einstein, 1905

11. Copyright © 2012 Pearson Education, Inc. Nuclear Fusion in the Sun (and All stars)

12. Copyright © 2012 Pearson Education, Inc. Weight of upper layers compresses lower layers.

13. Copyright © 2012 Pearson Education, Inc. Gravitational equilibrium: Gravity pulling in balances pressure pushing out. Energy balance: Thermal energy released by fusion in core balances radiative energy lost from surface.

14. Copyright © 2012 Pearson Education, Inc. Gravitational contraction… provided energy that heated the core as the Sun was forming. Contraction stopped when fusion started replacing the energy radiated into space.

15. Copyright © 2012 Pearson Education, Inc. How does nuclear fusion occur in the Sun?

16. Copyright © 2012 Pearson Education, Inc. Fission Big nucleus splits into smaller pieces. (Nuclear power plants) Fusion Small nuclei stick together to make a bigger one. (Sun, stars)

17. Copyright © 2012 Pearson Education, Inc. High temperatures enable nuclear fusion to happen in the core.

18. Copyright © 2012 Pearson Education, Inc. The Sun releases energy by fusing four hydrogen nuclei into one helium nucleus. The new He nucleus is less massive than the original 4 Hydrogen atoms.

19. Copyright © 2012 Pearson Education, Inc. Proton–proton chain is how hydrogen fuses into helium in the Sun.

20. Copyright © 2012 Pearson Education, Inc. IN 4 protons OUT 4 He nucleus 2 gamma rays 2 positrons 2 neutrinos Total mass is 0.7% lower.

21. Copyright © 2012 Pearson Education, Inc. 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.

22. Copyright © 2012 Pearson Education, Inc. 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.

23. Copyright © 2012 Pearson Education, Inc. How does the energy from fusion get out of the Sun?

24. Copyright © 2012 Pearson Education, Inc. Energy gradually leaks out of the radiation zone in the form of randomly bouncing photons.

25. Copyright © 2012 Pearson Education, Inc. Solar Structure and Solar Activity

26. Copyright © 2012 Pearson Education, Inc. The Sun goes through periods of relative activity and inactivity (X-ray images)

27. Copyright © 2012 Pearson Education, Inc. The Sun’s interior has three layers: (1) core (2) radiative zone (3) convective zone Energy generated in the core of the Sun propagates outward through these different layers, and finally, through the atmosphere of the Sun. This process takes tens of thousands of years or more.

28. Copyright © 2012 Pearson Education, Inc. The Sun’s atmosphere also has three layers… Photosphere - the layer we see, 5800 K Chromosphere - the red layer observed using a hydrogen filter, 10,000 K Corona - the incredibly thin outer atmosphere, 1,000,000 K

29. Copyright © 2012 Pearson Education, Inc. The photosphere is the visible layer of the Sun Granulation caused by convection http://www.whfreeman.com/universe6ehttp://www.whfreeman.com/universe6e - Seething Granules around a Sun Spot

30. Copyright © 2012 Pearson Education, Inc. Sunspots are the most well known feature in the photosphere. Monitoring sunspots reveals the Sun’s rotation. http://www.whfreeman.com/universe6ehttp://www.whfreeman.com/universe6e - the motion of a small sun spot

31. Copyright © 2012 Pearson Education, Inc. The movement of sunspots reveals that the Sun’s rotation takes about … 4 weeks

32. Copyright © 2012 Pearson Education, Inc. Maximum number Minimum number The annual change in numbers of sunspots reveals that the Sun experiences an 11-year Sun Spot cycle

33. Copyright © 2012 Pearson Education, Inc. Magnetic field lines connect sunspots on the Sun’s photosphere

34. Copyright © 2012 Pearson Education, Inc. Solar magnetic fields also create other atmospheric phenomena prominences solar flares

35. Copyright © 2012 Pearson Education, Inc. The corona, the outermost part of the Sun’s atmosphere, is characterized by its high temperature and low density The Sun also ejects a stream of charged particles into space known as the solar wind

36. Copyright © 2012 Pearson Education, Inc. Solar magnetic fields also create other atmospheric phenomena prominences solar flares coronal mass ejections (CMEs)

37. Copyright © 2012 Pearson Education, Inc. http://www.spaceweather.com/ http://www.spaceweather.com/images2002/18mar02/cme_c3_big.gif

38. Copyright © 2012 Pearson Education, Inc. The most powerful solar flare in 14 years,.. erupted from sunspot 486 in late October of 2003. The explosion hurled a coronal mass ejection almost directly toward Earth, which triggered bright auroras when it arrived on Earth.

39. Copyright © 2012 Pearson Education, Inc. The Earth’s magnetic field is caused by movement of material in Earth’s interior

40. Copyright © 2012 Pearson Education, Inc. Sun’s Magnetic Field Effects The Earth

41. Copyright © 2012 Pearson Education, Inc. The Earth’s magnetic field produces a magnetosphere that deflects and traps particles from the solar wind protecting Earth

42. Copyright © 2012 Pearson Education, Inc. Relevance of Earth’s protective magnetosphere Protects against Solar Flares - violent explosions on the Sun releasing large burst of charged particles into the solar system Protects against Solar Wind - dangerous stream of charged particles constantly coming from the Sun Northern Lights (Aurora Borealis) –Caused by the solar wind interacting with the magnetosphere.

43. Copyright © 2012 Pearson Education, Inc. Northern Lights (Aurora Borealis) As the charged particles from the Sun interact with the magnetic field around Earth, the particles collide with the nitrogen and oxygen atoms in the atmosphere and excite those atoms to emit light See Mastering Astro animation

44. Copyright © 2012 Pearson Education, Inc.

46. Aurora as seen from space