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Tolbert2 - back in time(however long it takes the light...

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Astronomy January 18, 2008 Lecture 2 Star- big balls of gas with fusion reactions occurring in their centers. These reactions give energy to the systems they are a part of. Each galaxy has approximately 100 billion stars or so. Avg distance from earth to sun is an astronomical unit of measure. (AU). 93 million miles, give or take. Light year-light travels at a certain, finite speed. Light speed is fastest through a vacuum, and it is constant when in a vacuum. 186,000 miles per second. Takes 8 minutes for light to reach earth to sun or vice versa. o One can also say it takes 8 light-minutes for light to reach the sun from the earth. Light year- distance light would travel in a year. o Keep in mind light years and light distances are measures of DISTANCE and not TIME. Closest star to us other than the sun is 4.5 light years away. Rapid brightening of a star is known as a supernova, when the star explodes before it goes out. Nearest galaxy to ours is 2 million light years away. Since light takes so long to get from other stars to us, we are actually looking
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Unformatted text preview: back in time (however long it takes the light from that star to get to us) when we look at stars. • Parsec- not as direct a measurement as a light-year. • Almost everything we know of the universe comes from the study of light. • There are only 3 properties you can learn from light o Position- stars are scattered in the sky, you can make a map of that. o Brightness- some stars are brighter than others when looking in the sky. o Spectrum (color)- some lights are yellow, some are red, etc. o From these 3 basic parameters of stars, we can figure out everything else we know about the universe. • What is light? What is it physically, what does it do? • There are only 2 ways to produce action at a distance? Exchanging or transmitting particles (chalk or bowling balls). Other way is to transmit a wave. o Sound waves require air to carry a wave. o Light waves do not. Thus, light must be particles....
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