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Unformatted text preview: Key Concept 1: Light Travel Time • Light travels at a finite speed(300,000 km/s), unit of distance • Thus, we see objects as they were in the past: the farther away we look in the distance, the further back we look in time o If far enough away, some of the things we see may no longer be there • Moon: 1 second • Sun: 8 Minutes • Sirius: 8 years • Andromeda Galaxy: 2.5 million years • Front of class: 10-100 billionths of a second • Light Year: o Distance light can travel in one year o Speed of light x 1 year o 9.461 x 10^12 km o 31 million seconds in a year • How far can we see? o 14 billion light-years – light from objects further from that has not had time to reach us o looking back 15 billion years is looking at a time before the universe existed o looking back before space was transparent is another problem – became transparent 300,000 years after universe formed...
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- Spring '11
- Astronomy, Supermassive black holes