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LightTravelTime - Key Concept 1 Light Travel Time Light...

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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 How is Earth moving in our solar system?
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