24.2 The Sun and the Seasons

Figure 7 Earth is constantly moving in two ways. A Earth rotates around its axis once a day. B Earth revolves around the sun once a year.

d

No one can feel it, yet Earth is constantly moving in space. Earth moves in two major ways: rotation and revolution. As shown in Figure 7A, Earth spins like a top around an imaginary line, or axis, that connects the north and south geographic poles. The poles are the two points at opposite ends of Earth where Earth's axis intersects the surface. The spinning of Earth on its axis is called rotation. Earth's rotation causes day and night. As Earth rotates from west to east, the sun appears to move from east to west across the sky. As Earth continues to spin toward the east, the sun sets in the west and night falls. It takes one day, or just under 24 hours, for Earth to complete one rotation.

As Earth rotates on its axis, it also travels around the sun, as shown in Figure 7B. Revolution is the movement of one body in space around another. It takes Earth one year, about $365\genfrac{}{}{0.1ex}{}{1}{4}$ days, to complete a full revolution around the sun. Earth revolves around the sun in a broad path, or orbit.

Table of Contents