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The Sun

The Sun. Properties. M = 2 X 10 30 kg = 300,000 M Earth R = 700,000 km > 100 R Earth 70% H, 28% He T = 5800 K surface, 15,000,000 K core. Structure. Sun’s Atmosphere. Sun’s Atmosphere. Solar Wind – stream of particles blown out from the sun Corona

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The Sun

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  1. The Sun

  2. Properties • M = 2 X 1030 kg = 300,000 MEarth • R = 700,000 km > 100 REarth • 70% H, 28% He • T = 5800 K surface, 15,000,000 K core

  3. Structure

  4. Sun’s Atmosphere

  5. Sun’s Atmosphere • Solar Wind – stream of particles blown out from the sun • Corona • Extends several million km above surface • T = 1,000,000 K • Emits X-Rays • Chromosphere • T = 10,000 K • Emits UV • Photosphere • T = 5,800 K • Emits visible light

  6. Sun’s Interior • Convection Zone • Energy travels up toward the surface via rising hot gas • Radiation Zone • Photons travel through plasma 1/3 down from surface • Core • Energy is produced

  7. Sun’s Interior • Convection Zone • Energy travels up toward the surface via rising hot gas • Radiation Zone • Photons travel through plasma 1/3 down from surface • Core • Energy is produced

  8. Energy • Measured in joules or calories • Power is the rate energy is used • 1 Watt = 1 joule/s • We call the power output of a star it Luminosity • LSun = 3.8 X 1026 watts

  9. Hydrostatic Equilibrium • Why doesn’t gravity just make the whole star collapse? • Gravity pulls in • Pressure from inside the sun pushes out • These two things balance perfectly

  10. How does the Sun shine?

  11. Historical Views • Burning ball of coal or wood • Energy release due to gravitational contraction • Kelvin-Helmholtz contraction

  12. Nuclear fusion • E=mc2 • Cloud of gas collapsed, releasing potential energy • Gas heats • Gravity creates high pressure • High pressure and temperature allow nuclear fusion

  13. Need high temperature so particles move fast enough to collide • Nuclear strong force keeps particles stuck together

  14. Proton-Proton Chain

  15. Solar Neutrinos

  16. Solar Thermostat

  17. Random Walk • Radiation has to make it out of the sun • Photon bounces randomly off of electrons • Density of Sun’s core means lots of bounces • Photons take a few hundred thousand years to get out

  18. Solar Activity

  19. Magnetic Fields • Material can travel along magnetic field lines • It is difficult to travel across field lines

  20. Sunspots

  21. Solar Prominence

  22. Solar Prominence Video

  23. Solar Flare • Sometimes magnetic fields get too stretched and can’t handle the stress anymore • They break, releasing trapped material • Video

  24. Coronal Mass Ejections

  25. CME Video

  26. Sunspot Cycle • Cycle lasts ~11 years • 7-15 yrs

  27. Sunspot Cycle

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