Ch 08 - Chapter 8 The Sun Stars Stars are simple Huge balls...

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Chapter 8 The Sun
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Stars Stars are simple Huge balls of hot gas held together by their own gravity Gravity tries to collapse them into small dense bodies High temperatures create high pressures that try to explode them The life of a star is an interplay between the two effects If the effects of self gravity and thermal pressure are balanced, the star is stable If there is an imbalance, major changes occur
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Striking a Balance Stars begin as a cloud of gas undergoing gravitational collapse Same heating process, once proposed to power stars, does cause the core of stars to get hot and dense, enough to start nuclear fusion reactions Once begun, fusion reactions generate energy which provides an outward thermal pressure Outward pressure perfectly balances the inward force of gravity Deep inside stars, pressure is strongest where gravity is strongest Near the surface, pressure is weakest where gravity is weakest This balance is called gravitational equilibrium Causes the star’s size to remain stable
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The Sun Star at the center of our solar system Glowing ball of gas held together by its own gravity Gas in plasma state Self-luminous, powered by nuclear fusion at its center Currently stable: the outward pressure generated by released energy is balanced by the inward pressure of gravity Source of light that distinguishes night from day Source of energy that powers: Life Weather Climate
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Why Study the Sun? Connection to climate Space weather Model Physical laboratory
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Connection to Climate Source of light and heat for life on Earth Changes in the Sun influence life on Earth Quantity and quality of light from the Sun varies on time scales from milliseconds to billions of years Connection not well understood
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Space Weather Source of the solar wind: A flow of gases from the Sun that streams past the Earth at speeds of more than 500 km/s (1 million mph) Disturbances in the solar wind shake the Earth’s magnetic field and pump energy into the radiation belts Regions on the surface of the Sun often flare and give off ultraviolet light and x-rays that heat up the Earth’s upper atmosphere Can change the orbits of satellites and shorten mission lifetimes The excess radiation can physically damage satellites and pose a threat to astronauts Shaking the Earth’s magnetic field can also cause current surges in power lines that destroy equipment and knock out power over large areas
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Model The Sun serves as a model for studying other astronomical objects It is the only star close enough to us to reveal details about its surface We know the Sun’s age, radius, mass, and luminosity (brightness), and have also learned detailed information about its interior and atmosphere This information is crucial for our understanding of other stars and how they evolve Many physical processes that occur elsewhere in the
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Ch 08 - Chapter 8 The Sun Stars Stars are simple Huge balls...

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