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chapter14 - Our Star The Sun Why was the Suns energy source...

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Our Star – The Sun
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Why was the Sun’s energy source a major mystery?
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Is the Sun on FIRE?  If it is on fire, it must be burning a chemical fuel. How  long can this burning last given it has a finite  mass  with a maximum chemical energy content?
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Is the Sun on FIRE?  Luminosity ~  10,000 years Chemical Energy Content
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Is it on FIRE?  … NO!  It would burn to an ash is 10,000 years! Luminosity ~  10,000 years Chemical Energy Content from Mass
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Is the CONTRACTING due to its own gravity?
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Luminosity Gravitational Potential Energy ~  25 million years
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Luminosity Gravitational Potential Energy Is it CONTRACTING?  … NO! ~ It would only last 25 million yrs
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Why does the Sun shine?
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It can be powered by NUCLEAR ENERGY! Luminosity ~  10 billion years Nuclear Potential Energy (core) E = mc 2 - Einstein, 1905
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The Sun has layers that get more dense as they go in toward the center What started the nuclear reaction? GRAVITY Things get hotter as they get compressed!!!
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Weight of upper layers  compresses lower layers
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Gravitational  equilibrium: Energy provided  by fusion  maintains the  pressure
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Gravitational  contraction: Provided energy  that heated core  as Sun was  forming Contraction  stopped when  fusion began
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What is the Sun’s structure?
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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
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Solar wind: A flow of  charged  particles from  the surface of  the Sun
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Corona: Outermost  layer of solar  atmosphere  ~1 million K
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Chromosphere: Middle layer of  solar atmosphere ~ 10 4  - 10 5  K
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Photosphere: Visible surface of  Sun ~ 6,000 K
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