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lecture13_ch10 - Radius 6.9 x 108 m(109 times Earth Mass...

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1 Our Star Radius: 6.9 x 10 8 m (109 times Earth) Mass: 2 x 10 30 kg (300,000 Earths) Luminosity: 3.8 x 10 26 watts Why does the Sun shine? Lifetime Prediction Predicted life = Energy Available Rate of Energy Loss = Energy Available Luminosity Chemical Energy: 4 x 10 38 J Estimated life expectancy ~ 30,000 years Gravitational Energy: 4 x 10 41 J Estimated life expectancy ~ 30,000,000 years Nuclear Energy: 1 x 10 46 J Estimated life expectancy ~ 100 billion (10 11 ) years Nuclear Energy: 1 x 10 46 J (x10% of the total actually available, in the core:) Estimated life expectancy ~ 10 billion (10 10 ) years Sun’s Energy Content Chem. energy = 4 x 10 38 J (~ 30,000 yr) Grav. energy = 4 x 10 41 J (~ 30 million yr) Nuclear energy = 1 x 10 44 J (~ 10 billion yr) Mass-energy = 2 x 10 47 J (~ 10 trillion yr)
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2 Fission Big nucleus splits into smaller pieces (Nuclear power plants) Fusion Small nuclei stick together to make a bigger one (Sun, stars) What is the Sun’s structure? Solar wind: A flow of charged particles from the surface of the Sun Corona: Very hot outer atmosphere of Sun (10 6 K): X-rays! Chromosphere: Hot inner atmosphere of Sun (10 4 -10 5 K): UV ! Photosphere: “Surface” of Sun from which visible photons escape: Visible ! 5800 K
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3 Convection zone: Hot gas rises and cool gas sinks Radiation zone: Million-degree gas, intense X-rays Core: Gas at 15 million Kelvin, nuclear fusion reactions Review: What is Gas Pressure?
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