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

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Visible Image of the Sun The Sun 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 center.
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Pressure (from heat caused by nuclear reactions) balances the gravitational pull toward the Sun’s center. This balance leads to a spherical ball of gas, called the Sun . What would happen if the nuclear reactions (“burning”) stopped?
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Main Regions of the Sun
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Radius = 696,000 km (100 times Earth) Mass = 2 x 1030 kg (300,000 times Earth) Av. Density = 1410 kg/m3 Rotation Period = 24.9 days (equator) 29.8 days (poles) Surface temp = 5780 K Solar Properties Solar Properties The Moon’s orbit around the Earth would easily fit within the Sun!
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Luminosity of the Sun = L SUN Solar constant: L SUN / 4 π R 2 (energy/second/area at the radius of Earth’s orbit) (Total light energy emitted per second) ~ 4 x 10 26 W 100 billion one- megaton nuclear bombs every second!
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The Solar Interior “Helioseismology” In the 1960s, it was discovered that the surface of the Sun vibrates like a bell Internal pressure waves reflect off the photosphere Analysis of the surface patterns of these waves tell us about the inside of the Sun How do we know the interior  How do we know the interior  structure of the Sun? structure 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 takes over again
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Convection Convection takes over when the gas is too opaque for radiative energy transport.
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