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Unformatted text preview: the sum total of all matter and energy; that is everything within the galaxy How can we know what the universe was like in the past? Light travels at a finite speed (300,00 km/s) Moon- light travels 1 second Sun- Light travels 8 minutes Sirius- Light Travels 8 years Andromeda Galaxy- Light travels 2.5 million years Light-year- A The distance light can travel in one year A About 10 trillion km (6 trillion miles) At great distances, we see objects, as they were when the universe was much younger 1 light year = (speed of light) x (1 year)...
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- Spring '07