If you look out from an empty field into a dark sky, you will get the impression that you are standing on a flat plate, enclosed by a giant dome. Depth perception fails us for the distant objects we see in the sky. This creates the appearance that all of the stars have the same distance. The stars all appear to move together across the sky during the night, rising in the east and setting in the west, as if they are affixed to the inside of the dome. Because of this phenomenon, many ancient civilizations believed that a dome really did enclose the Earth. Only a few centuries ago astronomers realized that the stars are actually very far away, scattered throughout the Milky Way Galaxy, rather than attached to the inside of a vast sphere. The old idea remains useful, however. The concept of the celestial sphere provides a simple way of thinking about the appearance of the stars from Earth without the complication of a realistic model of the universe.