The Moon seems to change shape — Science, 4–6 years
The Moon is round, but we see different amounts of its sunlit half as it moves around Earth.
The Moon has phases
The Moon is a round rocky world, not a flat shape that grows and shrinks. Sunlight always lights up half of it, but from Earth we see different amounts of that bright half. These changing views are called phases, such as new moon, crescent, half moon and full moon.
Why does the Moon look different?
People noticed that the Moon’s bright shape changes in a repeating pattern, which helps us notice the passing of time. The change is not because the Moon makes its own light or because Earth’s shadow covers it every night. It happens because the Moon moves around Earth while sunlight lights it from one direction.
Model a full moon
Use a lamp as the Sun, a ball as the Moon and your head as Earth. Step 1: turn the ball so one half faces the lamp. Step 2: stand with your back to the lamp and hold the ball in front of you. Step 3: you can see the whole lit half, so the model shows a full moon. Move the ball to your side and only part of its bright half is visible.
The Moon is not growing
A crescent can look like a smaller Moon, and a full moon can look like a bigger one. It is reasonable to think the Moon itself is growing and shrinking, because that is what our eyes seem to show. In fact, the round Moon stays about the same size; our changing view of its sunlit side makes the shape appear different.
Watching the Moon outdoors
You can keep a Moon diary by drawing its shape and writing the date each time you see it. Notice whether it appears in the evening or morning, and compare your drawings after several weeks. Clouds, trees and buildings can hide it, so one missed night does not mean the Moon has vanished.
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