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Light Travel Time: Because of the finite speed of light, we see more distant objects as they were in the past. For example, we see the star Alpha Centauri as it was 4.4 years ago, and the Andromeda Galaxy as it was 2.5 million years ago. Astronomers are often asked how we know that these objects still exist when we look at them in the night sky. How would you try to answer this question?
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