What is a Light-Year? Explained Simply

A light-year is the distance that a beam of light travels in a vacuum over the course of one year. It's used by astronomers to measure the vast distances between stars and galaxies. For example, the nearest star to our Sun, Proxima Centauri, is about 4.24 light-years away. That means the light we see from it today actually left the star over four years ago.

 

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