1. Ch. 6: The Sun

2. Chemical energy? The Sun’s luminosity is about 4x10 26 joules per second. Its mass is about 2x10 30 kg. What is its energy source?

3. Chemical energy? The Sun’s luminosity is about 4x10 26 joules per second. Its mass is about 2x10 30 kg. What is its energy source?

4. = 10 Cal/g = 10 8 J/kg 2x10 30 kg 4x10 26 Joules second 10 8 joules kg x 1 year 3x10 7 seconds x

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

6. It can be powered by NUCLEAR ENERGY! Luminosity ~ 10 billion years Nuclear Potential Energy (core) E = mc 2 - Einstein, 1905

7. The fusion of hydrogen via the proton-proton chain positron neutrino 4 He nucleus Neutrinos created during fusion fly directly through the Sun Observations of these solar neutrinos can tell us what’s happening in core

8. Weight of upper layers compresses lower layers

9. The Sun is in hydrostatic equilibrium Gravity pushes inward Fusion generates energy - heats the gas - increases the pressure - balances the inward force of gravity

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

11. Radiation Zone: Photons don’t know which way is up - they escape by a “random walk” Energy gradually leaks out of radiation zone

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

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

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

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

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

17. Limb darkening

18. The layers of the Sun are determined by how energy is transported through and out of that layer Radiation transport (radiative transfer)

19. Sunspots cooler than other parts of the Sun’s surface (~4000 K) Contain strong magnetic fields cool gas is sinking

20. 41.2 Zeeman effect Atomic energy levels, and their spectral lines, are split when the atoms are in a magnetic field Experimental confirmation of the quantization of angular momentum

21. Why do the lines split? Magnetic moment of a current carrying loop: I Current I = charge/time Electrons are moving charges They respond to external B Their energy levels change when in a B Potential energy of this interaction:

23. Loops of bright gas often connect sunspot pairs X-ray emission

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

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

26. Corona appears bright in X-ray photos in places where magnetic fields trap hot gas Insert TCP 5e Figure 14.20

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

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

30. Number of sunspots rises and falls in 11-year cycle Solar activity varies with time

31. Little Ice Age 1300-1850 Winter sports became very popular!

32. Historical implications of the Little Ice Age Greenland settlement collapsed in 1400 Glaciers advanced, crushing villages in Switzerland 1780: New York Harbor froze Stradivari built his famous violins Armies could march acropss frozen rivers and straits Snow fell in summer in Northern Europe: famine ensued