Stars are too far away to use kilometers or miles to measure their distances, so astronomers use light-years instead. One light-year is nearly 10 million million km, and the nearest star, Proxima Centauri, is 4.25 light-years distant. The farthest heavenly bodies are at the unimaginahble distance of 8,000 million light-years! As the earth moves around the sun, the nearer stars appear to move very slightly in relation to the distant stars. The farther apart they are, the greater the parallax (apparent movement) appears to be. By observing the various movements, astronomers are able to calculate the approximate distances of the stars from earth.