The moon and Earth both revolve and rotate on their way around in our solar system, but what is the difference between the two movements?

Rotation is when a planet or moon turns all the way around or spins on its axis one time. The axis of rotation is an imaginary line going from the north pole to the south pole. When a planet or moon travels once around an object this is considered a revolution. On Earth, a rotation is pretty short - it happens once a day! It is the rotation that makes the sun appear to come up in the morning and set at night. On Earth, a revolution is quite a bit longer - one year!

The moon is a little different. The moon rotates once about every 27 days, and revolves once about every 27 days. So every time the moon goes around Earth it turns around one time. That is why the moon always looks the same - we only ever see one side of it! Another strange thing is that if we lived on the Moon and thought of days and years the same way we do on Earth, a day AND a year would be the same length! Since the rotation and revolution times are the same, the length of a day and the length of a year are identical.

Here is a test to see if you can tell the difference between a rotation and a revolution:

In the above picture, which object is rotating?

Which object is revolving?

What is the imaginary line that Earth rotates upon?

One rotation of Earth is a and one revolution of Earth is a .

Extension: Modeled after “Simon Says”

Materials:

• A group of friends

Procedure:

1. Everyone needs to stand for this activity.
2. One person plays the role of “leader”
3. When the leader says ”rotate”, everyone demonstrates it by twirling their index finger.
4. When the leader says “revolve”, everyone demonstrates it by moving their index finger around in a broad circle in front of them.
5. An individual loses when he or she becomes confused.
6. This person must now sit down.
7. Those remaining continue in the activity until there is only one left standing. He or she wins and can become the new leader if you want to do it again.
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