Pick one before you read on. It is fine to be wrong.
By the end you can
Model the phases of the Moon with a ball and a lamp
Draw the Moon each night for two weeks and name the phases
Explain why the Moon looks upside down in the other hemisphere
Some nights the Moon is a thin curve. A week later it is a half circle. Later it is a full circle. How can this be?
The Moon does not change. It is always a ball.
The Sun always lights half of the Moon. A torch lights half of a ball in the same way.
The Moon goes round the Earth. So each night we look at it from a new place. We see more or less of the lit half.
Draw it first
Draw why the Moon changes shape
1 Draw the Sun on the left and the Earth in the middle. Draw a ring round the Earth.
2 Draw the Moon in four places on the ring. Draw a line down the middle of each.
3 Draw sunlight reaching each Moon from the left. Shade the half that faces away from the Sun.
4 Write each name: new, half growing, full, half shrinking. Add an arrow on the ring.
Look at the Moon on the left. It is between the Earth and the Sun. Its lit half faces the Sun. We see the dark half. We cannot see this Moon. It is a new Moon.
The Moon on the right is far from the Sun. The Earth is between them. We see its whole lit half. It is a full Moon.
At the top and bottom the Moon looks half lit. Between new Moon and half Moon, we see a thin curve. A thin curve is a crescent.
The shape we see each night is a phase. The phases go round and round.
See it three ways
As a picture
In words
The Moon grows from new to full in about two weeks. Then it shrinks back to new in about two more.
Make a Moon diary. Start on the first evening you can see a thin Moon.
Look at the Moon at about the same time each clear evening. Draw it in a circle. Shade the dark part. Do this for two weeks.
If clouds hide the Moon, leave that circle empty. After full Moon, it rises later each night. Look a little later.
Write the name under each drawing. Use new Moon, crescent, half Moon, over half and full Moon.
One page of a Moon diary. Each circle is one evening.
Try it
Make the phases with a ball and a torch
You need: a torch, a pale ball, or a stone wrapped in white paper, a room you can make dark, a shelf or chair for the torch.
Be safe: Never shine the torch into anyone's eyes. Never look at the Sun. Do this indoors with a torch only.
Stand the torch on a shelf and switch it on. Make the room dark.
Stand a few steps from the torch. Hold the ball high at arm's length.
Face the torch. Look at the ball. The lit side faces away from you.
Turn slowly to your left. Stop at each quarter turn.
At each stop, draw the lit part in a circle.
What you will see: The lit part of the ball changes as you turn. First you see a dark ball. Then half is lit. Then the whole near side is lit. Then half again. The torch always lights half of the ball.
If you cannot try it, this is what happens.
People in the north and in the south see the same Moon. But they see it turned round.
North and south are opposite ends of the Earth. People there have their heads pointing opposite ways. So they see the Moon turned half way round.
In the north, a growing Moon is lit on the right. In the south, it is lit on the left.
The same phases, seen from the north and the south.
Near the equator, a thin Moon can lie on its back. It looks like a boat.
Turn a picture of the Moon upside down. You see the Moon as people in the other half see it.
A wrong idea many people have
The phases of the Moon are the Earth's shadow on the Moon.
Why it feels right: The dark part of the Moon looks like a shadow.
The test that breaks it: In the ball and torch test, you hold the ball high. Your head makes no shadow on it. The ball still goes through every phase. So no shadow is needed.
What is true: The Sun always lights half of the Moon. We see more or less of the lit half. The Earth's shadow falls on the Moon only in an eclipse.
Key words
phase
the shape of the lit part of the Moon that we see.
new Moon
the Moon between us and the Sun. Its lit half faces away from us.
full Moon
the Moon on the far side of the Earth. We see its whole lit half.
crescent
a thin curved shape.
Back to your guess
The answer is C: We see more or less of its lit half.
The Moon is always a ball. The Sun lights half of it. We see more or less of that half.
Check yourself
Try each one before you look. A wrong answer tells you where to go next.
What makes the Moon change shape?
See the answer
We see more or less of its lit half.
The Sun lights half of the Moon. The Moon goes round. We see a different amount of that half.
If you chose B: The Earth's shadow falls on the Moon only in an eclipse. The ball and torch test needs no shadow.
If you chose C: The Moon is always the same ball. Only the part we see is different.
Where is the Moon at full Moon?
See the answer
On the far side of the Earth from the Sun
From the Earth we see the whole lit half.
If you chose A: That is new Moon. The lit half faces away from us.
If you chose C: The Moon is in the Earth's shadow only in an eclipse. A full Moon is lit.
Ana lives far south of the equator. The Moon is growing towards full. Which side is lit?
See the answer
The left side
People in the south see the Moon turned round. A growing Moon is lit on the left.
If you chose B: That is how it looks in the north. In the south the Moon is the other way up.
If you chose C: A growing Moon is not yet full. Only part of it is lit.
A new Moon is on day 0. New Moon to new Moon takes 29 and a half days. About which day is the full Moon?
See the answer
About day 15
The full Moon is about half way round. Half of 29 and a half is nearly 15.
From an earlier chapter
The Moon shines. Where does its light come from?
See the answer
The Sun
The Sun lights the Moon. The Moon reflects some of that light to us.
If you chose A: The Moon makes no light. It sends back sunlight. Go to S2.9.5.
If you chose C: The light comes from the Sun. The Moon only sends it back. Go to S2.9.5.
Draw the Moon you saw last. Write its name.
See the answer
A circle with the dark part shaded. A name: new Moon, crescent, half Moon, over half or full Moon.
The shape of the lit part gives the phase its name.
The picture shows the Moon between the Sun and the Earth. What do we see from the Earth?
See the answer
A new Moon. We see its dark half.
The Sun lights the half of the Moon that faces the Sun. From the Earth we see the other half, which is dark.
If you chose A: At full Moon the Earth is between the Sun and the Moon. Here the Moon is between the Earth and the Sun.
If you chose B: A half Moon is off to the side. Here the Moon is in line with the Sun and the Earth.
If you chose C: A crescent shows when the Moon is just off the line. Here it is on the line.
After a full Moon, what do we see on later nights?
See the answer
Less and less of the lit half, night after night
The Moon keeps going round. Each night we see less of its lit half, until new Moon.
If you chose A: A full Moon shows all of the lit half. There is no more to see. After that we see less.
If you chose B: The Moon looks full for only a night or two. Then we see less of its lit half.
If you chose C: The change is slow. Each night we see a little less of the lit half.
Keep it
Copy this into your exercise book.
The Moon is always a ball. The Sun lights half of it. As it goes round, we see more or less of that half. These are its phases. North and south see it upside down.
Draw: Draw the Sun, the Earth and a ring. Put the Moon on the ring in four places. Shade the half of each Moon that faces away from the Sun.
