Why does the Moon look slightly different each night? It is because we are all in motion. This is even a somewhat difficult concept for an adult because it surely does not feel like we are moving!
The best way to explain this is to use three balls: A large beach ball (the Sun), a soccer ball (the Earth) and a tennis ball (the Moon). Mark the soccer ball with an X indicating where you live.
1. One student holds the Sun in the middle of the room. Remind students that the Sun is a medium star and our source of light and heat. The force of gravity holds the Earth in an orbit around the Sun.
2. Now have the second student hold the Earth several yards from the Sun. The Earth rotates on its axis and revolves around the Sun. So the student should slowly spin and move around the Sun at the same time.
3. Student three has the Moon and should be placed a few feet from the Earth. The Moon rotates (spins) and revolves around the Earth while the Earth revolves around the Sun.
4. Freeze frame! Stop everyone. From where you live, where is the Sun and where is the Moon? Remember that the Moon reflects the light from the Sun. From where we live, we only see a certain part of the lighted surface because everything is moving.
5. A full Moon is when the Earth is between the Sun and the Moon and we can see the whole lighted surface.
6. Keep a calendar for a month and in each square draw a picture of what the moon looks like. The phases will range from new(totally dark), crescent, half, gibbous and full.