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The Moon and stars

Space and time · level 1, lesson 4 of 6

A question to start

Some nights the Moon is a big round ball. Other nights it is a thin curve, like a banana. Is the Moon really changing shape?

The idea

No. The Moon is always a round ball. It does not make its own light; it shines because the Sun lights it up.

The Moon goes round the Earth. As it does, we see different amounts of its sunny side:

  • When we see the whole sunny side, there is a full Moon.
  • When we see only a sliver, there is a thin crescent.
  • When the sunny side faces away from us, we can hardly see the Moon at all: a new Moon.

From one full Moon to the next takes about 29 and a half days: about a month. The word "month" comes from "Moon".

The stars are suns, very far away. They are in the sky in the daytime too, but the Sun is so bright we cannot see them.

newcrescenthalffull

Worked examples

1. A month. From one full Moon to the next is about 29 and a half days.

2. Two weeks. Half of that, about 15 days, takes the Moon from new to full.

3. Daytime Moon. Sometimes you can see the Moon in the daytime too, pale in the blue sky.

Try it

  1. Does the Moon make its own light?
  2. About how long is it from one full Moon to the next?
  3. What is a thin Moon called?
  4. Why can we not see stars in the daytime?
Answers
  1. No. The Sun lights it up.
  2. About 29 and a half days.
  3. A crescent.
  4. The Sun is so bright that it hides them.

Common mistake

"The Earth's shadow makes the Moon's shapes." The shapes come from how much of the Moon's sunny side we can see. The Earth's shadow only falls on the Moon during an eclipse.

Where it leads