Light traveling in empty space is the fastest thing in the universe. It travels at 186,000 miles per second!
The stars are so far away from us that their light still takes a long time to reach Earth. One light year is the distance light travels in a year: 5,878,499,812,499 miles. The closest star apart from the Sun is 4.2 light years away, so its light takes 4.2 years to reach Earth.
Tell the Birthday Stars computer when you were born, and it will look for a star that is your age in light years away from Earth. This means that the light we're seeing from that star today actually left the star around when you were born, and has taken your entire life to reach Earth.
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