CHO7 - Twopossibilitiesexist:EitherwearealoneintheUniverseor

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Two possibilities exist: Either we are alone in the Universe or  we are not. Both are equally terrifying.  -- Arthur C. Clarke
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Unknowingly, we plow the dust of stars, blown about us by  the wind, and drink the universe in a glass of rain. --- Ihab Hassan
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"The sun, with all those planets revolving around it and  dependent on it, can still ripen a bunch of grapes as if it had  nothing else in the universe to do." --- Galileo
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The Sun Chapter 7:
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Sun is the source of life on Earth. All forms of energy on Earth are either direct or conserved forms of the energy we receive from the Sun (solar, wind, coal, oil, natural gas…) Fossil fuels are created by decomposition of dead organisms which owe their existence to the Sun
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General Properties Average star Absolute visual magnitude = 4.83 (magnitude if it were at a distance of 32.6 light years) Central temperature = 15 million K 333,000 times Earth’s mass 109 times Earth’s diameter Consists entirely of gas (average density = 1.4 g/cm 3 ) Only appears so bright because it is so close Spectral type G2 Surface temperature = 5800 K
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Facts about the Sun Diameter: 1.4 million kilometers Surface temperature: 5800K Spectral Type: G Rotation period: 25 days (equator) 35 days (poles) Mass: 2.0 × 10 30 kg (300,000 earth masses!) Mean density: 1.4 g/cm 3 (water is 1.0 g/cm 3 ) Density at surface: 10 -6 g/cm 3 (air is 0.001 g/cm 3 ) Density at core: 160 g/cm 3 (lead is 13 g/cm 3 )
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1.4 × 10 6 km The sun in visible light
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The surface of the Sun Photons trapped inside the Sun From photosphere they can freely stream out Mean free path of photons = 400km It takes 1 000 000 years for photon to travel from the center to the surface
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The Photosphere The solar corona Depth ≈ 500 km Temperature ≈ 5800 K Apparent surface layer of the Sun Highly opaque (H - ions, strong interaction with photons) Absorbs and re-emits radiation produced in the solar interior
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sunspot T = 4200K The surface of the Sun photosphere T = 5800K
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granules
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Energy Transport in the Photosphere Energy generated in the Sun’s center must be transported outward. Convection (direct contact) Bubbles of hot gas rising up Cool gas sinking down In the photosphere, this happens through ≈ 1000 km Bubbles last for ≈ 10–20 min.
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Granulation … is the visible consequence of convection.
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Convection
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Convection Q. How do we know granules are convection?
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Convection Q. How do we know granules are convection? A. Doppler shift! redshift blueshift
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The Solar Atmosphere Only visible during solar eclipses Apparent surface of the Sun Heat Flow Solar interior Temperature increases inward
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Energy of the Sun comes from its mass: E=mc^2 The sun is losing 4.3×10 9 kg of mass every second! (equal to ~10 supertankers) At this rate, the sun would run out of fuel after ~ 10 11 years. Compute the rate at which the sun is losing mass, given
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This document was uploaded on 11/03/2011 for the course PHY 122 at SUNY Buffalo.

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CHO7 - Twopossibilitiesexist:EitherwearealoneintheUniverseor

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