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The Moon and Its Phases
Have you noticed that the Moon looks different from night to night? Sometimes it is a full, round circle. Sometimes it is a thin curve, and some nights you cannot see it at all. In this lesson you will learn about our Moon and why its shape seems to change.
Our Moon
The Moon is a rocky ball that travels around Earth. Something that orbits a planet is called a moon or natural satellite. Our Moon is about a quarter as wide as Earth, and about 384,000 kilometres away.
The Moon has no air, no liquid water and no weather. Its surface is covered with grey dust and craters. Because there is no wind or rain, astronauts’ footprints from many years ago are still there!
The Moon does not make its own light
The Moon does not glow by itself. It reflects sunlight, like a mirror reflects a torch. The bright part of the Moon is the part lit by the Sun.
Why does the Moon change shape?
The Moon takes about 29 and a half days to go through all its shapes. As it travels around Earth, we see different amounts of its sunlit side. These changing shapes are called phases.
| Phase | What we see |
|---|---|
| New Moon | almost nothing, the lit side faces away from us |
| Waxing crescent | a thin curve of light, growing |
| First quarter | half of the Moon lit |
| Waxing gibbous | more than half lit, growing |
| Full Moon | the whole face lit |
| Waning gibbous | more than half lit, shrinking |
| Last quarter | half lit on the other side |
| Waning crescent | a thin curve, shrinking |
Waxing and waning
Waxing means the lit part is growing bigger each night. Waning means it is shrinking. After the waning crescent, the cycle starts again with a new Moon.
Model the phases at home
You can see how phases work with a simple model:
- In a dark room, put a lamp on one side of the room. This is the Sun.
- Hold a ball at arm’s length. This is the Moon. Your head is Earth.
- Turn slowly in a circle, keeping the ball in front of you.
- Watch how much of the lit side of the ball you can see as you turn.
Example
When Noah faced the lamp with the ball in front of him, the ball looked dark: a new Moon. When he turned with his back to the lamp and held the ball up high, it was fully lit: a full Moon. In between, he saw crescents and half Moons.
The Moon and the tides
The Moon’s gravity gently pulls on Earth’s oceans. This pull helps cause the tides, the rising and falling of the sea along the coast each day.
Key takeaways
- The Moon is a rocky natural satellite that orbits Earth.
- It shines by reflecting sunlight.
- Its phases repeat about every 29 and a half days.
- Waxing means growing; waning means shrinking.
Practice
- Where does moonlight really come from?
- What is the phase called when the whole face of the Moon is lit?
- What does “waning” mean?
Answers: 1 is the Sun, because the Moon reflects sunlight. 2 is a full Moon. 3 is that the lit part is getting smaller each night.