Figure 2-4: Why Diurnal Motion Happens The diurnal (daily) motion of the stars, the Sun, and the Moon is a consequence of Earth’s rotation. (a) This drawing shows Earth from a vantage point above the north pole. In this drawing, for a person in California the local time is 8:00 p.m. and the constellation Cygnus is directly overhead. (b) Four hours later, Earth has made one-sixth of a complete rotation to the east. As seen from Earth, the entire sky appears to have rotated to the west by one-sixth of a complete rotation. It is now midnight in California, and the constellation directly over California is Andromeda.