Fixed star is an expression often used in referring to the stars, because their places in the sky relative to one another do not seem to change. Actually, the stars are moving in many directions, and the pattern of the heavens is slowly changing. But the changes are scarcely noticeable within a person’s lifetime, because the stars are so far away. Even Barnard’s star, the one believed to move the fastest, changes position by a distance equal only to the moon’s diameter in 200 years. Compared to the planets, which can be seen constantly shifting in the sky, the starry background seems “fixed.”
Astronomers use photography and sighting telescopes to study the motions of all of the bright stars and many of the faint ones. In photographs taken at different times many years apart, they compare the positions of the stars and note how the stars have changed. The astronomers can then tell how the constellations (groups of stars) will change in the future.
