The Earth / Moon / Sun System

NC Standard:  3.02, 3.05

Activity:  Fun with Phases

Question: What causes the phases of the moon?

Vocabulary: reflection, phases, movement, shadow

Background: The moon orbits around Earth once every 27-30 days. During this time, the moon moves eastward about 13° per day. (just bigger than a fist at arms length), making the time of the moonrise later each day. From Earth, we see it as the moon changing position in the sky and changing the percent of the illuminated side we are able to see (called phases). At any given time, half of the moon has sunlight hitting it (the day side of the moon) and the half not facing the sun is dark. How much of the illuminated moon we can see from Earth determines the phase of the moon. The basic phases are New, First Quarter, Full, Last Quarter, and back to New. First Quarter occurs and we continue to see more of the moon until we see the entire illuminated side at Full Moon. The phases move to Last Quarter, and then the New Moon and we begin the cycle all over again. As the moon orbits around the Earth, it also rotates on its axis. We only see one side of the moon because it keeps the same side facing Earth. If it didn't rotate as it orbited Earth, we would see both sides of the moon. The side we see from Earth is the "nearside of the moon" and the side we never see from Earth is the "far side of the moon".

Materials: Styrofoam ball, pencil, flashlight

Procedure: 

• 1. Stick the pencil into the Styrofoam ball.

• 2. Draw a big X on one side of the ball. This marks the side we always see from Earth.

• 3. Explain that the ball is the moon, the flashlight is the sun, and the person holding the ball is Earth.

• 4. Have student Earth move, holding out the moon at arms length slightly over his / her head, until the moon is directly between the sun and Earth.

• 5. What phase is the moon in now? New moon - the side of the ball that faces Earth is dark.

• 6. Student Earth, stil holding the moon at arms length in front of and above his / her head, turns so his / her back is to the sun (flashlight).

• 7. What phase is the moon now? Full moon - the side of the ball that faces Earth is now completely lit.

• 8. Student Earth now moves very slowly counterclockwise until the student sees a thord quarter phase, then a crescent, and back to a new moon.
  

Conclusion: Light, movement, and shadow result in the phases of the moon.
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Line of Learning:  This line is drawn to provide students with a space to share their experimental learning in words or pictures.
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