Why Does the Moon Change Shape?

Lesson Plan - Get It!

Audio:

Every night, looking up at the moon, you should see something different.

The shape of the moon depends on its position in relationship to the earth and the sun.

The moon is a satellite, a body that orbits, or revolves, around a larger body. When you can see all or part of the moon, it is because light from the sun is reflecting off its surface. The area that you are unable to see is not in a position to reflect the sun's light.

• What about those nights when you cannot see the moon at all?
• Where has it gone?

If you cannot see the moon, it is because it is positioned between the earth and the sun. In this position, the sun's light is shining on the side of the moon that is not facing the earth. Therefore, the sun's light is being reflected away from the earth, making the moon seem invisible.

You can perform a simple demonstration to see how the sun's light reflects off the moon, causing it to appear in different shapes.

1. Hold a kick-ball-sized ball at arm's length before you. This ball represents the moon, and you represent the earth.

2. Ask someone to shine a flashlight on the ball as they walk around you. They represent the sun. You should remain stationary while the other person moves.

3. As the other person moves, notice how the light shines on some parts of the ball while others remain dark.

4. Then, ask the person to stand facing you on the opposite side of the ball.

• When they shine the light on the ball, does any light show on the side of the ball facing you?

This is how the earth, moon, and sun are positioned when you cannot see the moon at night.

You are probably familiar with what a full moon looks like.

• But did you know that each of the moon's shapes has a name?

These are the phases of the moon. Look at the image below to see each of the moon's phases.

The new moon is the first phase of a lunar cycle. It takes about 29-30 days to complete one lunar cycle.

Learn more about the moon's phases as you watch the following video.

• Do you recognize each of the phases?

Pay attention to the moon during the next few days and see if you can identify the phases.

Keep it going in the Got It? section!