When we say something is 1000 light years away, or 100,000 light years away, how do we know how far light has traveled to reach us? How do we differentiate the distance between all the different sources of light we can see so accurately?
In: Physics
Space itself is always expanding, and this also makes the light itself expand. This translates to a change in the color of the light. We know the general colors coming from each star, so we can compute the change from that and get a time. It’s a process called redshift.
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