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Ch. 6: The Sun

Ch. 6: The Sun. The Sun’s luminosity is about 4x10 26 joules per second. Its mass is about 2x10 30 kg. What is its energy source?. 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?. Chemical energy?.

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Ch. 6: The Sun

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  1. Ch. 6: The Sun

  2. The Sun’s luminosity is about 4x1026 joules per second. Its mass is about 2x1030 kg. What is its energy source? Chemical energy?

  3. The Sun’s luminosity is about 4x1026 joules per second. Its mass is about 2x1030 kg. What is its energy source? Chemical energy?

  4. 4x1026 Joules 1 year x x 108 joules second 3x107 seconds kg = 10 Cal/g = 108 J/kg 2x1030 kg

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

  6. E = mc2 - Einstein, 1905 It can be powered by NUCLEAR ENERGY! Nuclear Potential Energy (core) ~ 10 billion years Luminosity

  7. positron neutrino 4He nucleus The fusion of hydrogen via the proton-proton chain • 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 ~ 104 - 105 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. Radiation transport (radiative transfer) The layers of the Sun are determined by how energy is transported through and out of that layer

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

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

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

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

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

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

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

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

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

  30. 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

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