Thousands of stars speckle the night sky. But even the closest of them shine from enormous distances. One way to measure these vast gulfs is the light-year — the distance light travels in one year. Because light speeds through empty space at a whopping 670 million miles per hour, a light-year is an enormous distance: nearly six trillion miles. One way to visualize this distance is to picture the difference between an inch and a mile. First, think of the distance between Earth and the Sun — about 93 million miles. Imagine that distance is only one inch. Now picture a long tape measure that stretches off into the distance. On this scale, all of the Sun’s planets would lie within just a few dozen inches of the Sun. But to travel the equivalent of a light-year, you’d need to walk an entire mile along that tape measure. The nearest star system to the Sun is Alpha Centauri, which is a bit more than four light-years away. Four may sound like a small number, but because a light-year is so larg
