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Measure the Moon

Measure the Moon Activity

See more activities in: Second Grade, Physical Science

Have your kids noticed how much bigger the moon looks when it's low in the sky? What's going on? The moon isn't changing size or getting closer: this is actually just an optical illusion. The moon takes up just about the same proportion of our field of vision no matter how high or low it is relative to the horizon.

If your kids don't believe you, here's a simple activity you can do to show them that the moon is always the same size. All you need is a paper clip to get started.

What You Need:

  • Paper clip
  • Clear night when the moon is low in the sky

What You Do:

  1. Help your child unbend the paper clip, then twist it into a U shape.
  2. When the moon is low in the sky, go outside and have her hold the paper clip at arm’s length in the direction of the low, large-looking moon. Show her how to use the paper clip like a pair of calipers, bending it so the tips are touching the top and bottom of the moon to record its apparent diameter.
  3. Wait an hour or more for the moon to climb higher in the sky.
  4. Go back outside and have your child hold her paper clip calipers at arm’s length again. What does she see? The moon should fit within the paper clip exactly.

If your kids liked this activity, try exploring other optical illusions by checking out a book on optical illusions from the library or researching them online.

Updated on Oct 12, 2012
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See more activities in: Second Grade, Physical Science
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