In this topic you will learn about how Earth's movement makes daytime and the seasons possible.

Earth is rotating, or spinning, on its axis. It rotates on its axis like a spinning top. The axis is an imaginary line through Earth from the North Pole to the South Pole. One rotation is a complete spin on an axis. It takes just about 24 hours for Earth to make one rotation. As a result of this motion, any location on Earth experiences a cycle of day and night.

The Sun's position in the sky changes during the day. As a day progresses, the Sun appears to rise in the east. It seems to travel west, rising higher in the sky as the day passes. At noon, the Sun reaches its highest point in the sky. After noon, it appears to get lower in the sky, until it sets in the west.

The International Date Line was created as the location where a new day begins. It is universally recognized. The International Date Line is the 180° line of longitude. If you cross the date line going west, you add a day.

You can tell time by knowing how many times Earth spins each day. Earth rotates 360° (one complete turn) in 24 hours. In one hour Earth turns 360°/24, or 15°. This defines a time zone. A standard time zone is a belt, 15° wide in longitude, in which all places have the same time.

When you cross time zones, you have to change your clock time. If you are traveling west in a jet you would set your watch back one hour for each time zone you cross. After 24 hours you are back home. However, the date on your watch is the same.

As a year progresses you observe the seasons change. You most easily notice this seasonal change as the average temperature rises and falls. This change is not caused by the change in distance between Earth and the Sun through the year. The motion of Earth around the Sun causes the change.

Earth takes 365 days to revolve, or travel in its orbit, once around the Sun. One complete trip around the Sun is called a revolution. While Earth is revolving it is also rotating on its axis. However the axis is not vertical. It is tilted at an angle of 23°. The effect of this tilt is the cycle of seasons.