Audio Guide：

Ancient people thought that the heavens were like a big sphere, with each star fixed onto its surface, like dots on a basketball; in fact they also called the sky the “heavenly sphere.” They believed that as the heavenly sphere spun around each day, the sun, moon, and the stars—all on the surface of the sphere—would travel from east to west. We know now that the heavens are not a sphere, but modern astronomers still use the concept of the sphere to define the position of each star they find.