Moon
Earth and Space

Why do we get day and night?

Teaching Guidance for 5-11 11-14 Supporting Physics Teaching

Common unhelpful approaches

Wrong Track: We get day and night so that we can sleep at night and do things in the day.

Wrong Track: It is when the Moon gets in front of the Sun and stops us getting sunlight and we call that night and then it moves and gives us the sunlight and we call that day.

Wrong Track: The Sun lights up the Earth so the Earth is shining brightly. It comes over the hills and mountains and when it starts to get dark the Sun goes back behind the hills and mountains.

Wrong Track: Because at night it isn't so warm and maybe the Sun goes behind a cloud.

Wrong Track: When the Sun comes to our side of the Earth, then it's day time.

Wrong Track: The Earth goes around the Sun every day. When it faces the Sun it's day.

Getting off along the right lines – a spinning Earth

Right Lines: The Earth spins on its axis, completing one turn a day. Day time for you is when your side faces the Sun.

Correct approaches and unhelpful starting points

Thinking about the learning

A reference to everyday life: We get day and night so that we can sleep at night and do things in the day.

Simple blocking explanations: These explanations all involve something getting in the way of the Sun, blocking its light and thereby creating the darkness of night. Common wrong tracks include arguing that the Moon, clouds or hills and mountains cause sunlight to be blocked.

Sun orbiting the Earth: Here the Earth is stationary and the Sun is in an orbit around it. According to this view, day-time comes when the Sun is on your side of the Earth and night-time when it is on the opposite side. For this model to work the Sun must orbit the Earth once a day.

Earth orbiting the Sun: Here the Sun is stationary and the Earth is in orbit around it. According to this view, day-time comes when your side of the Earth faces towards the Sun and night-time when it faces away from the Sun. It's the orbiting of the Earth around the Sun that is used here to explain day and night. For this model to work, the Earth must orbit the Sun once per day and also maintain the same orientation (facing the same way) in space, with no spinning. Here is a caricature of this suggestion.

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Thinking about the teaching

Here the Earth is spinning on its axis in front of the Sun, once every 24 hours. According to this view, day-time comes when your side of the Earth is facing towards the Sun and night-time when it faces away from the Sun. Here is a caricature of the model.

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Pupils' responses

Thinking about the teaching

There is an important progression in understanding here. For pupils to appreciate that the Earth is spinning, and that this is the cause of day and night, is a major step and suggests a more sophisticated understanding which you can build on.

Here are some responses from a mixed ability science class of 11-year-olds, before the year's work on the solar system, in a well established, rural comprehensive school to the challenge:

Teacher: Use words and diagrams to explain your ideas about why we get day and night.

These results suggest that it is worth probing your pupils' understanding of day and night right at the start of the teaching.

You might simply ask pupils to respond to the question:

Teacher: Why do we get day and night?

Alternatively you may wish to use a diagnostic question which actually confronts the pupils with possible alternative views and probes the link between ideas and evidence.

Moon
is a type of Satellite
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