As the moon goes through its phases, it looks a little different each night, ranging from not there at all to full. Your group will act out how the sun illuminates the moon as it orbits Earth, to understand how the moon moves through its phases.
The moon shines because it is reflecting the sun. So why doesn’t it always look the same? As it travels around Earth, the half of the moon facing the sun is always “lit up.” What we see depends on where the moon is in orbit, and the relative positions of Earth and the sun. For instance, when it is a new moon, the moon is between Earth and the sun with its bright side facing the sun and its dark side facing Earth. When the moon is full, and we see a full circle of light in the sky, Earth is between the moon and the sun—the moon’s bright side is facing us. It helps to look at a diagram to fully understand the phases of the moon and there is a good one at Clear Skies on Demand.
Ask students to share any observations they have made about the moon. Ask: “Have you noticed when it is full? Or that sometimes you can’t see the moon? Why do you think that is?”
Pull up the Clear Skies on Demand diagram and ask your group to gather around. A projector is recommended so that students can refer to the image as they do the activity. Or, you can have students make a poster that shows the phases.
Walk students through the diagram on your own (not necessarily with what is written on the website). First remind students that the moon orbits Earth and it takes 29.5 days to do so. Point to the new moon and state that the dark side of the moon faces Earth. Remind students that Earth rotates and at night they are on the side facing away from the sun. Now point out the full moon and state that the bright side faces Earth.
Before students do the activity on their own, ask a couple of students to help you demonstrate the activity. One student should be Earth, the other student should be the sun, and you can be the moon. Walk around the “Earth” slowly and have the “Earth” also spin around so that student can see what the moon looks like. Help the student describe what he or she is seeing. “Earth” will always have the best view of the moon phases but if positioned properly the onlookers should be able to see some phases.
Now have students carry out the activity in pairs.
Give each pair of students a flashlight, ball, stick, and the By the Light of the Moon activity sheet.
Have the students follow the directions from the activity sheet. Ask them to think about what they are seeing.
If you have to break students into bigger groups because there are not enough supplies, be sure each student gets a turn holding the “moon” so that they can see the phases.
After they've completed the activity, they can answer the questions posed at the end of their student sheet and, if there's time, you can discuss the answers as a group.
If the moon is just a big hunk of rock, where does moonlight come from? The answer is the sun! Sunlight reflects off the surface of the moon, so we can see if from the Earth. In this experiment, you'll see why the moon goes from full to dark and back again.