Lecture 6-Chapter 14-Our Star

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University of Toronto St. George
Astronomy & Astrophysics
Stefan Mochnacki

Chapter 14 Our Star Why Does the Sun Shine? N L3890L389K0474170O,9L;L99K0$:3.43;07982,88L3940307J9K74:JKnuclear fusion of hydrogen into helium. N So the Sun shines because it generates energy through nuclear fusion. N When the Sun was born, gravitational contraction made the Sun hot enough to sustain nuclear fusion in its core. N ;078L3.00307JOL-07,90-1:8L43K,82,L39,L309K0$:38gravitational equilibrium and kept the Sun shining steadily. What Keeps the Sun Stable in Size? N The sun keeps its core hot and dense through a natural balance between two competing forces: gravity pulling inward and pressure pushing outward gravitational equilibrium. N %K0$:38L39073,O57088:70570.L80O-,O,3.08J7,;L9,90;0754L39ZL9KL3L9 keeping the Sun stable in size. N The deeper into the Sun, with the greater weight of overlying layers, the greater the pressure. N %K:8005L39K0$:38.4709K057088:702,N089K0J,8K49,30380034:JK94 sustain nuclear fusion. N The released energy by fusion heats the gas and keeps the balance against the inward pull of gravity. DIAGRAM 14.2, pg 479. How Fusion Started? N When the sun was born 4.6 billion years ago from a collapsing cloud of interstellar gas, the contraction of the cloud released gravitational potential energy, causing the interior temperature and pressure to rise. N When the central temperature and density finally grew high enough to sustain 3:.O0,71:8L430307JJ0307,9L43L39K0$:38L3907L47.,20L394-,O,3.0ZL9K9K0 energy lost from the surface in the form of radiation. N This energy balance stabilized the size of the Sun gravitational equilibrium N Calculations show that the Sun was born with enough hydrogen in its core to shine steadily and maintain gravitational equilibrium for about 10 billions years. %K0$:38$97:.9:70 DIAGRAM 14.3 N %K0$:387,L:8L8,-4:9 NL982,88L8; ) NJ 9L2089K02,88 of Earth). N Rather than spinning and rotating at the same rate, the solar equator completes one rotation in about 25 days, increasing with latitude to about 30 days near the solar poles. N %K0$:38949,O54Z074:95:9luminosity is an incredible 3.8 X 10^26 watts. www.notesolution.com
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