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The_Sun - The Sun Visible Image of the Sun Our sole source...

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The The Sun Sun Visible Image of the Sun •Our sole source of light and heat in the solar system •A very common star: a glowing ball of gas held together by its own gravity and powered by nuclear fusion at its by nuclear fusion at its center.
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Pressure (from heat caused by nuclear caused by nuclear reactions) balances the gravitational pull d h toward the Sun’s center. Thi b l l d This balance leads to a spherical ball of gas, called the Sun . What would happen if h l i the nuclear reactions (“burning”) stopped?
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Main Regions of the Sun
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Radius = 696,000 km Solar Properties (100 times Earth) Mass = 2 x 10 30 kg Mass 2 x 10 (300,000 times Earth) Av Density = 1410 kg/m 3 Av. Density = 1410 kg/m Rotation Period = 24.9 days (equator) 29.8 days (poles) Surface temp = 5780 K The Moon’s orbit around the The Moon s orbit around the Earth would easily fit within the Sun!
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Luminosity of the Sun = L SUN (Total light energy emitted per second) ~ 4 x 10 26 W 100 billion one- megaton nuclear bombs every second! Solar constant: ! 2 L SUN 4 " R (energy/second/area t th di f at the radius of Earth’s orbit)
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The Solar Interior “Helioseismology” How do we know the interior structure of the Sun? •In the 1960s it was In the 1960s, it was discovered that the surface of the Sun ib t lik b ll vibrates like a bell •Internal pressure waves reflect off the waves reflect off the photosphere •Analysis of the Analysis of the surface patterns of these waves tell us b t th i id f th about the inside of the Sun
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The Standard Solar Model
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Energy Transport within the Sun Extremely hot core - ionized gas • No electrons left on atoms to capture photons - core/interior is transparent to light ( radiation zone ) • Temperature falls further from core - more and more non-ionized atoms capture the photons - gas becomes opaque to light in the convection zone • The low density in the photosphere makes it transparent to light - radiation k i takes over again
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Convection ! C i k h Convection takes over when the gas is too opaque for radiative energy transport. ! Hot gas is less dense and i ( “fl t ” lik h t i rises (or “floats,” like a hot air balloon or a beach ball in a pool).
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