Seasons are caused by the Earth's tilted axis, not its distance from the sun. Leaning towards the sun gives a higher noon sun (concentrated light) and longer days: summer. The two hemispheres have opposite seasons.
On 4 January the Earth is at its closest to the sun all year, five million kilometres closer than in July. That day it's summer in Canberra and winter in London.
The Earth's axis is tilted and always points the same way. This lesson: what that does across a year.
Engage: Commit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Explore: Try it on the board and compare what happens with your prediction.
Explain: Use the particle model to explain what you saw.
Practise: A few on your own, to check you have it.
Elaborate: Use the same idea in a new context.
Evaluate: Look back at your first ideas and what changed.
WidthMore contexts, same idea.
Make your prediction first. Help opens once you've locked it in.
EngageCommit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Engage: why is it hotter?
ExploreTry it on the board and compare what happens with your prediction.
Explore: December and June
Move the Date slider between December and June. Note the daylight, how high the sun is at noon, and the distance from the sun each time.
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Compare Canberra in late December and late June (daylight, noon sun and distance).
Use the board. This ticks when you get there.
ExplainUse the particle model to explain what you saw.
Explain: tilt, not distance
In your book: draw a torch shining straight down and at a slant onto paper. Use it to explain why a high sun heats the ground more.
Which go with Canberra's summer, and which with its winter?
Southern Hemisphere leans towards the sun
Noon sun high in the sky
About 9½ hours of daylight
Sunlight hits the ground at a low angle, spread over a bigger area
About 14½ hours of daylight
PractiseA few on your own, to check you have it.
Mix it up
PractiseA few on your own, to check you have it.
The other hemisphere
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Pick one date and compare London with an Australian city.
Use the board. This ticks when you get there.
Elaborate WiderUse the same idea in a new context.
Elaborate: no tilt
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Set the tilt to 0° and look at three different months.
Use the board. This ticks when you get there.
EvaluateLook back at your first ideas and what changed.
Evaluate: look back
Write one sentence: "At first I thought… Now I think… because…"
Revision summary
Seasons are caused by the Earth's tilt, not its distance from the sun (we are closest in January).
Leaning towards the sun: the noon sun is higher (light concentrated on a smaller area) and days are longer: summer.
The two hemispheres have opposite seasons. Near the equator the changes are small.
For teachers
Students explain seasons by the Earth's axial tilt, link tilt to the height of the noon sun and day length, and use opposite hemispheres and the distance data to reject the distance explanation (AC9S7U03, node 4, a hinge node). About 22 minutes.
I can explain that seasons are caused by the tilt, not distance from the sun.
I can link the tilt to the height of the noon sun and the length of the day.
I can explain why the two hemispheres have opposite seasons.
Before class
A concept tutorial for introducing or revising the idea; pair it with a torch shone straight and at a slant onto grid paper. Set the width with ?width=minimum, typical (default) or wider.
The hinge misconception is that summer happens because the Earth is closer to the sun. The board shows the real distance for each date: closest (147 million km) in early January, farthest (152) in early July.
Board notes: day lengths and noon sun heights are calculated for each city's latitude and date (ignoring the bending of light by the air, which adds a few minutes). The wider tier's tilt slider is a "what if": the real tilt is 23.4°. The Kakadu six seasons are described by Parks Australia with Bininj/Mungguy people; check local sources if you want students to explore a calendar from your own area.
Running the lesson
Engage: count how many chose 'closer to the sun'.
Explore: ask what the distance was in December and in June.
Explain: 'If distance caused seasons...' is the checkpoint.
The hard part (on purpose)
Explaining seasons by tilt, not distance. When a student says Earth is closer in summer, ask what the board says the distance is on 22 December and 22 June.
When students get stuck
A student says the Earth is closer to the sun in summer. Ask: What does the board say the distance is on 22 December and 22 June? Fix: Closer in December by about 5 million km, out of 150: and London is in winter then.
A student says summer is hotter only because days are longer. Ask: What about the height of the noon sun? Fix: Both: a higher sun concentrates the light, and longer days give more hours of it.
Stretch and support
Stretch: Why are the days around the equinoxes (about 20 March and 22 September) close to 12 hours everywhere?
Support: Give a table: date, daylight, noon sun height, distance, season, to fill for December and June.
Where it leads
Next: the moon (nodes 2, 3 and 5).
In class: the torch-and-grid-paper practical; a sunrise and sunset table for your town from the Bureau of Meteorology or Geoscience Australia.
What each step is for
Engage: why is it hotter?: The distance misconception is persistent; students who hold it will choose 'closer', and the board's distance readout contradicts it.
Explore: December and June: Reading daylight, noon sun height and distance for both solstices puts the evidence against distance in front of the student.
Explain: tilt, not distance: Linking tilt to sun angle and day length, and confronting distance with evidence, is the hinge.
Mix it up: The tilt that causes the seasons only works because the axis keeps pointing the same way as the Earth goes round the sun.
the other hemisphere: Seeing opposite seasons on the same date in London and Canberra is the strongest evidence for the tilt explanation.
Elaborate: no tilt: Removing the tilt in the model and watching the seasons disappear shows tilt is the cause, not just a correlation.
Now you can
Explain that seasons are caused by the tilt, not distance from the sun.
Link the tilt to the height of the noon sun and the length of the day.
Explain why the two hemispheres have opposite seasons.