The distance from the earth to the nearest star is four and one half light-years. A light-year is about six million million miles—or 6,000,000,000,000 miles! Now, if the stars are this vast distance away from us, how can we measure how big they are, what they’re made of, and so on?

At one time, the only instrument the astronomers had was the telescope. Today, a whole group of special instruments exists to help astronomers study the motions, brightness, color, temperatures, and composition of the stars.