Lecture13 - The Sun Radius 6.9 x 108 m(109 times Earth Mass...

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1 The Sun 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 • Over 99.9% of solar system’s mass. • Made mostly of H/He gas (plasma). • Converts 4 million tons of H mass into energy each second. Why does the Sun shine? Is it on FIRE? Is it on FIRE? Luminosity ~ 10,000 years Chemical Energy Content Is it on FIRE? … NO! Luminosity ~ 10,000 years Chemical Energy Content
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2 Is it CONTRACTING? Luminosity Gravitational Potential Energy Is it CONTRACTING? ~ 25 million years Luminosity Gravitational Potential Energy Is it CONTRACTING? … NO! ~ 25 million years Is it powered by NUCLEAR ENERGY? Luminosity ~ 10 billion years Nuclear Potential Energy (core) Is it powered by NUCLEAR ENERGY? … YES! Luminosity ~ 10 billion years Nuclear Potential Energy (core) E = mc 2 - Einstein, 1905 Gravitational equilibrium: The outward push of pressure balances the inward pull of gravity
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3 Weight of upper layers compresses lower layers Gravitational equilibrium: Energy provided by fusion maintains the pressure Gravitational
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