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Announcements

Announcements. Wednesday night star parties begin this week, 8:45 pm, weather permitting. Attend one for 4 points extra credit! (Staff signature required.) 10:00 office hour cut short today Majors Fest at Union Building Gallery. Nuclear Reactions in Stars (part 2). 1 November 2006. Today :.

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Announcements

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  1. Announcements • Wednesday night star parties begin this week, 8:45 pm, weather permitting. Attend one for 4 points extra credit! (Staff signature required.) • 10:00 office hour cut short today • Majors Fest at Union Building Gallery

  2. Nuclear Reactions in Stars (part 2) 1 November 2006

  3. Today: • What makes the stars shine? • How long do they last? • Then what happens?

  4. The Sun’s Interior Thermonuclear energy zone Radiative zone Convective zone

  5. The Sun’s Interior Nuclear reactions only take place in the innermost 30% of the sun’s radius. The central density is 150 times that of water; the central temperature is 15 million kelvin.

  6. In summary… The sun is a mass of incandescent gas, A giant nuclear furnace, Where hydrogen is built into helium At a temperature of millions of degrees. -- Zim and Baker, A Golden Guide to Stars, 1951; borrowed by They Might Be Giants, 1993

  7. Can we test any of this theory? Yes! Look for the neutrinos…

  8. Fusion of Hydrogen into Helium 4 1H (protons) 4He This reaction powers all main-sequence stars. The more massive the star, the more pressure at its center and therefore the faster the reaction occurs.

  9. Masses of Stars

  10. Sizes of Main-Sequence Stars Hottest stars are actually somewhat larger Should be white, not green! Reds are greatly exaggerated!

  11. Main Sequence Lifetimes(predicted)

  12. What happens when the core of a star runs out of hydrogen? • With no energy source, the core of the star resumes its collapse… • As it collapses, gravitational energy is again converted to thermal energy… • This heat allows fusion to occur in a shell of material surrounding the core… • Due to the higher central temperature, the star’s luminosity is greater than before… • This increased energy production causes the outer part of the star to expand and cool (counterintuitive!)… • We now have a very large, cool, luminous star: a “red giant”!

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