Chapter 14 Section 1 What are the motions of Earth? Objective: Explain Earth’s motion

Key Terms revolution: movement of a planet or other body orbiting another body axis: imaginary line through the center of a planet or other body around which that body spins rotation: spinning of a planet or other body on its axis

Revolution Although you cannot feel it, Earth is always moving. It moves in an orbit around the Sun. One complete revolution around the Sun takes 365 ¼ days, or one year. Earth’s path as it goes around the Sun is called its orbit. As Earth travels around the Sun, Earth’s orbit forms a slightly flattened circle, or oval, shape.

DESCRIBE What is the motion of Earth around the Sun called?

Rotation Besides revolving, Earth also spins on its axis. Earth’s axis is tilted at an angle of 23 ⅓° relative to an imaginary line drawn perpendicular to its orbit. The North Pole of Earth always points toward Polaris, the North Star.

Rotation Our planet rotates once every 24 hours. This gives us a daily cycle of daylight and darkness, or day and night. The side of Earth’s surface that faces the Sun has daylight. The side that faces away from the Sun has darkness. At any moment, half of Earth is experiencing daylight. The other half is experiencing darkness.

2. IDENTIFY What is the motion of Earth on its axis called?

Sunrise and Sunset When viewed from the North Pole, Earth rotates on its axis from west to east. This makes the Sun appear to rise in the east and set in the west. As Earth rotates, the Sun seems to move across the sky from east to west. This is called the Sun’s apparent motion.

3. RELATE In which direction does Earth rotate?

Classwork CHECKING CONCEPTS How long does it take Earth to make one complete revolution around the Sun? What causes the change from day to night? Why does the Sun appear to rise in the east? At what angle is Earth’s axis tilted?

Classwork THINKING CRITICALLY 5. CONTRAST: How is rotation different from revolution? 6. DESCRIBE: What is the shape of Earth’s orbit? 7. PREDICT: What would happen if Earth did not rotate? 8. INFER: Like the Sun, the Moon seems to rise in the east and set in the west. Why?