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# Rotation of Earth

## Earth rotates on its axis, which creates the day-night cycle.

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Rotation of Earth

What would you do if you were in Paris?

Take a view from the top of the Eiffel Tower? March up the stairs to eye the gargoyles at Notre Dame? Nibble on coffee and croissants in a sidewalk cafe? Visit Foucault's Pendulum in the Pantheon? Yes! When in Paris, don't forget to go to the Pantheon and visit this testament to Earth's rotation.

### Foucault's Pendulum

Foucault's Pendulum is at the Pantheon in Paris, France.

In 1851, a French scientist named Léon Foucault took an iron sphere and hung it from a wire. He pulled the sphere to one side and then released it, as a pendulum. Although a pendulum set in motion should not change its motion, Foucault observed that his pendulum did seem to change direction relative to the circle below. Foucault concluded that Earth was moving underneath the pendulum. People at that time already knew that Earth rotated on its axis, but Foucault's experiment was nice confirmation.

### Earth’s Rotation

Imagine a line passing through the center of Earth that goes through both the North Pole and the South Pole. This imaginary line is called an axis . Earth spins around its axis, just as a top spins around its spindle. This spinning movement is called Earth’s rotation .

An observer in space will see that Earth requires 23 hours, 59 minutes, and 4 seconds to make one complete rotation on its axis. But because Earth moves around the Sun at the same time that it is rotating, the planet must turn just a little bit more to reach the same place relative to the Sun. Hence the length of a day on Earth is actually 24 hours.

At the Equator, the Earth rotates at a speed of about 1,700 km per hour, but at the poles the movement speed is nearly nothing.

### Day-Night Cycle

Earth rotates once on its axis about every 24 hours. To an observer looking down at the North Pole, the rotation appears counterclockwise. From nearly all points on Earth, the Sun appears to move across the sky from east to west each day. Of course, the Sun is not moving from east to west at all; Earth is rotating. The Moon and stars also seem to rise in the east and set in the west.

Earth’s rotation means that there is a cycle of daylight and darkness approximately every 24 hours, the length of a day. Different places experience sunset and sunrise at different times and the amount of daylight and darkness also differs by location.

Shadows are areas where an object obstructs a light source so that darkness takes on the form of the object. On Earth, a shadow can be cast by the Sun, Moon, or (rarely) Mercury or Venus.

### Summary

• Foucalt's pendulum shows that Earth moves beneath a swinging pendulum.
• Earth rotates on its axis every 24 hours.
• Earth rotates so that the Sun, Moon, and stars appear to travel from east to west each day.

### Interactive Practice

Use these resources to answer the questions that follow.

1. Why does the Earth spin?

2. Why has the Earth's spin slowed?

3. What will eventually happen to the Moon?

4. How long does it take for the Earth to complete a rotation?

5. What direction is the Earth rotating?

### Review

1. How does Foucalt's pendulum show that Earth rotates on its axis?

2. Why do the Sun, Moon, and stars appear to rise in the east and set in the west each day?

3. Why does the Equator travel at a speed of 1,700 km per hour and the poles not travel at all?

### Vocabulary Language: English Spanish

axis

axis

An imaginary line that runs from the North Pole to South Pole, and it includes the center of Earth.
rotation

rotation

The motion of the Earth spinning on its axis.