How can we measure things about the stars?

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. First of these is the camera, which is used to make permanent records of the stars observed. Another instrument is the spectrograph. This is used to photograph the spectra of the stars, or the rays of light coming from them. With the help of the spectrograph, astronomers have learned most of what they know about what the stars are made of, their temperatures, and the speeds at which they are moving.