Lecture_11

Lecture_11 - A Closer Look at the Sun Our Goals for...

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1 A Closer Look at the Sun A Closer Look at the Sun • Our Goals for Learning The Sun is a star : • Why does the Sun shine? • What is the Sun’s structure? LUMINOSITY = TOTAL ENERGY EMITTED PER SECOND (watts) Each second the Sun emits the equivalent of current human energy demands for next 500,000 years! Is it on FIRE? … NO! Luminosity ~ 10,000 years Chemical Energy Content Luminosity Gravitational Potential Energy Is it CONTRACTING? … NO! ~ 25 million years Is it powered by NUCLEAR ENERGY? … YES! Luminosity ~ 10 billion years Nuclear Potential Energy (core) E = mc 2 - Einstein, 1905
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2 Gravitational equilibrium: The Sun is a huge ball of hydrogen and helium gas. The outward push of pressure balances the inward pull of gravity Remember the pillows? Explains why Jupiter and Saturn are almost same size. Weight of upper layers compresses lower layers Energy provided by nuclear fusion maintains the pressure balance against gravity. contraction: Provided energy that heated core as Sun was forming and slowed contraction. Contraction stopped when fusion began. The Role of Gravity in 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 Sunspots Dark limb shows Sun has a thinner outer atmosphere
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3 Solar wind: A flow of charged particles from the surface of the Sun Corona: Outermost layer of solar atmosphere. Very thin. ~1 million K Chromosphere: Middle layer of solar atmosphere ~ 10 4 -10 5 K Photosphere: Visible “surface” of Sun. This is as far into the Sun as we can see. ~ 6,000 K
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4 Convection Zone: Hot, dense turbulent gas. Energy transported
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This note was uploaded on 02/20/2012 for the course ASTRO 3 taught by Professor Mclean during the Spring '11 term at UCLA.

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Lecture_11 - A Closer Look at the Sun Our Goals for...

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