physics 55 friday, october 28, 2005 1.the sun as a star. 2.structure of the sun. 3.nuclear reactions...
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Physics 55Friday, October 28, 2005
1. The Sun as a star.2. Structure of the Sun.3. Nuclear reactions that power the Sun.4. How do we know what we know?
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Talk by Dr. Jocelyn Bell Burnell TonightUNC 7pm Morehead Planetarium
Jocelyn Bell in 1968
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Mars, the Pleiades, Taurus, the Hyades
WARNING: Do not confuse the star Aldebaran in Taurus with Alderaan, the home planet of Princess Leia in the Star Wars movies!
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Mars Won’t Be This Close for 13 Years
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Our Sun as a Star: Chapter 15
Why does it shine?What is its structure?
How are the elements produced?How does the Sun affect Earth?
How do we know what we know?
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Particular Properties of the Sun
Note: Total human energy consumption about 1011 watts
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Structure of the Sun
15,000,000 K
6000K
10,000 K
1,000,000 K
Who remembers role of solar wind in formation of solar system?
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Other Stars Have Similar Structures
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What Determines the Size of the Sun?Gravitational Equilibrium
Balance of gravitational forcetoward center and pressure outward (from thermal motion):“gravitational equilibrium”“hydrostatic equilibrium”
column,
2
or
versus
r r
PV NkT
P nkT
m MG
d
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Attempts to Estimate Lifetime of Sun in 1800s Led to a Mystery: Too Short!
“Calculating the age of the Earth and Sun” by Arthur Stinner,
Physics Education 37(4) 296-305 (2002).
30 7
26
2 10 kg of coal 3 10 J/(kg coal) 5,000 y
4 10 J/s
Helmholtz: Assume Sun with mass 1030 kg is made of combusting coal:30 7
26
2 10 kg coal 3 10 J/(kg coal) 5,000 y
4 10 J/s
Kelvin’s meteoric theory: energy of Sun supplied by meteors steadily falling into Sun, releasing gravitational potential energy. Anyone see a way to test this idea?
Kelvin and Helmholtz: Assume energy released by conversion of gravitational potential energy into kinetic energy of mass falling inward toward center: ~ 60,000,000 years with Sun shrinking only about 80 m in radius per year.
All known mechanisms fail to give age consistent with geology and biology of billions of years, what is going on?
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Radioactivity
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Nuclear Reactions