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The Sun

The Sun. Topics. Sunshine Solar Features SOHO Mission Summary. Fig. 10-9a, p. 205. p. 200. Mass 2 x 10 30 kg Diameter 1.4 million km Surface Temperature 5800 K Composition (by mass) 75% Hydrogen 25% Helium 0.1% heavier elements. Central Temperature 15 million K

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The Sun

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  1. The Sun

  2. Topics • Sunshine • Solar Features • SOHO Mission • Summary

  3. Fig. 10-9a, p. 205

  4. p. 200

  5. Mass 2 x 1030 kg Diameter 1.4 million km Surface Temperature 5800 K Composition (by mass) 75% Hydrogen 25% Helium 0.1% heavier elements Central Temperature 15 million K Central Pressure 200 billion atmospheres Age 4.6 billion years Basic Properties

  6. Power Output • Unit of Power • 1 Watt = 1 Joule/second • 100 Watt light bulb = 100 Joules/second • Sun’s power output • 3.826 x 1026 Watts • How do we know this? • Measure the Solar Irradiance, that is, the power received per square meter on Earth, 1366.5 Watts/m2 • Multiply by the area of a sphere of radius 1 AU.

  7. Earth R = 1AU Sun Estimating Sun’s Power Output • Area of Sphere • 4pR2 • Solar Power • Area x Solar Irradiance • 4p(1.5 x 1011 m)2 x 1366 • ~ 4 x 1026 Watts

  8. Sunshine

  9. What Makes the Sun Shine ? • 1871 – Hermann von Helmholtz • The solar energy output is equal to the energy released by burning 1500 lb of coal per hour for every square foot of the Sun’s surface!

  10. p. 213

  11. What Makes the Sun Shine ? – II • 1919 – Sir Arthur Eddington • Showed that the conversion of hydrogen to helium could provide enough energy to explain the power of the Sun. • 1930s – Hans Bethe, Carl von Weizsäcker • Developed Eddington's ideas and showed that nuclear fusion could produce the required power.

  12. E = mc2 Luminosity = 4 x 1026 Watts E = mc2 → m = E / c2 Mass destroyed / second = Luminosity / c2 = 4 x 1026 J/s / (3x108 m)2 ~ 4 x 109 kg/s = 4 million metric tons/second !

  13. The Proton-Proton Nuclear Chain 1H + 1H → 2H + e+ + n e+ + e- → g + g 2H + 1H → 3He + g 3He + 3He → 4He + 1H + 1H 4H →4He Deuterium creation 3He creation 4He creation

  14. Fig. 10-3, p. 202

  15. Solar Opacity • Light • Ironically, the Sun is opaque to light! The degree of “opaqueness” is called the solar opacity. • Because of the Sun’s high opacity, it takes about one million years for the light created in the Sun’s core to reach the surface! • Neutrinos • On the other hand, the neutrinos get out in a matter of seconds. 60 billion of them cross every square centimeter per second on Earth.

  16. Super Kamiokande: Solar Neutrinos Solar neutrino Electron

  17. Solar Features

  18. Fig. 10-2, p. 202

  19. Fig. 10-16, p. 208

  20. Fig. 10-5a, p. 204

  21. The Sunspot Cycle Fig. 10-18, p. 208

  22. Fig. 10-11, p. 206

  23. Fig. 10-4, p. 203

  24. The SOHO Mission

  25. The Orbit of SOHO Lagrangian Point (L1)

  26. SOHO Images (1999) movie

  27. Summary • Sun • The Sun is the closest star to Earth. • It is a ball of ionized gas at temperatures ranging from 15 million K in the core to about 6000 K at its surface. • The Sun is made of ¾ Hydrogen and ¼ Helium, by mass. • Sunshine • Light arises from the nuclear fusion of hydrogen to helium in the core and takes about a million years to reach the surface.

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