1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 1 Announcements: Spring Break: next week!! Exam #2: Thursday, April 5 th ! Chp. 3, 11

2. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 2 The Sun as a Star (Chp. 11)

3. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 3 The Maunder Minimum refers to a) Times of low solar activity that occur every 11 years. b)Times of low solar activity that occur every 22 years c)The region in the solar atmosphere where the temperature is lowest. d)An extended period of time in the 1600’s during which the Sun had anomalously low activity levels.

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5. 5 The Sun’s activity cycle is a result of: a) Magnetism and Differential Rotation b) Gas Pressure and Differential Rotation c) Coupling of the magnetic field of the Earth and Sun. d) Global Warming

6. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 6 Differential Rotation plays important role in 11-year cycle: Rotation period at equator: 25 days Rotation period at poles: 36 days

7. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 7 What is the source of the Sun’s energy?

8. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 8 The Sun produces its energy from a)Electric currents generated in its core b)Chemical reactions (oxidation reactions) producing flames c)Fusion of hydrogen into helium d)Disintegration of helium into hydrogen

9. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 9 1 H+ 1 H  2 H+e + + e 2 H+ 1 H  3 He+  3 He+ 3 He  4 He+2 1 H What’s missing? a) 1 H b) 2 H c) 3 He d) 4 He ?

10. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 10 1 H+ 1 H  2 H+e + + e 2 H+ 1 H  3 He+  3 He+ 3 He  4 He+2 1 H Slowest reaction Most energetic reaction Proton-Proton Chain

11. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 11 How long can the Sun keep shining?

12. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 12 What you started with: 4 hydrogen atoms (protons) What you end up with: 1 helium atom (2 protons and 2 neutrons) Mass Deficit: 0.048 × 10 -24 grams (or 0.7%) Proton-Proton Chain (cont) mass= 6.693 × 10 -24 grams mass= 6.645 × 10 -24 grams

13. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 13 Proton-Proton Chain (cont) Only 0.7% of the mass is converted into energy! Fortunately, the Sun has a lot of mass! Unfortunately, only the innermost 10% is hot enough for fusion to take place…

14. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 14 How much mass will be converted into energy? Mass of Sun = 2.0x10 33 grams

15. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 15 How much energy is that? Energy = mc 2 = 1.3 × 10 51 ergs Funny energy units!

16. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 16 Sun is losing 3.9x10 33 ergs of energy every second! How long can it keep this up?! Total Energy Available = 1.3 × 10 51 ergs Every second, Sun emits 3.9 × 10 33 ergs 3.3 × 10 17 seconds = 10 billion years!

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18. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 18 Once you create all of that energy, how do you get it out?

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20. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 20 Conduction: Particle collisions transfer energy

21. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 21 Radiation: Heating (or cooling) by absorbing (or emitting) photons.

22. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 22 Convection: Circulation (taking hot material and putting it someplace else) often due to buoyancy

23. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 23 Where the various processes take place

24. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 24 Solar Granulation is a result of convection

25. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 25 Sunspots Revisited

26. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 26 Strong, localized magnetic forces stop convection Energy from within the Sun, therefore, doesn’t get to the surface Sunspots are small regions in the photosphere that are slightly cooler than their surroundings. Why are sunspots dark?

27. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 27 Photons Take a Random Walk in the Radiative Zone Each time they collide, they lose a little energy

28. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 28 Photons: Thousands of Years Neutrinos: 2 seconds Photons versus Neutrinos

29. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 29 How do we know what the interior of the Sun is like? Study solar neutrinos Study sun-quakes Experiments detect half as many as were expected by theory, but experiments and theory converging. Oscillations tell us what the structure of the solar interior is like. Structure agrees with theory.

30. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display 30 Sun-quakes!!