KS3 · Physics

Seasons and Earth's tilt

Right now it can be freezing in Britain and beach weather in Australia — same planet, same Sun, same moment. Distance can't explain that. A lean can.

One trip round the Sun, one fixed tilt

1North leans in2Neitherleans in3South leans in4Neitherleans again

Stage 1 of 4: North leans in. paused

North leans in · 1/4scrub round the orbit →

The axis tips the Northern Hemisphere towards the Sun. The north gets summer: the Sun climbs high and days are longer than nights. The south is leaning away, so it has winter — at the very same moment.

Picture Earth's axis as a pencil through the North and South Poles, always pointing at the same far-off spot in space. Scrub Earth round its orbit and watch which half ends up leaning towards the Sun.

Two halves, one moment

Hemisphere tilted towards the SunvsHemisphere tilted away from the Sun

Read across each row: whenever one hemisphere is tilted towards the Sun, the other is in the opposite condition.

Focus

How high the Sun climbs

Hemisphere tilted towards the Sun

High in the sky at midday

Hemisphere tilted away from the Sun

Low in the sky, even at midday

The insight

This is the difference people miss. The Sun doesn't just shine for longer in summer — it climbs higher in the sky.

Day compared with night

Hemisphere tilted towards the Sun

Days longer than nights

Hemisphere tilted away from the Sun

Days shorter than nights

Season

Hemisphere tilted towards the Sun

Summer

Hemisphere tilted away from the Sun

Winter

Why summer is warmer

?

Reason it through

Why does the ground heat up more in the hemisphere tilted towards the Sun?

Link 1 of 3

First link · your turn

The hemisphere is tilted towards the Sun. How does sunlight arrive there?

2
Locked — reveal the link above first
3
Locked — reveal the link above first

What do you really think?

What actually causes the seasons?

Right now it's summer in one hemisphere and winter in the other. Your explanation has to cope with both at once.

Which is closest to what you think right now?
How sure are you?

Rebuild the year

Tick what's true for each hemisphere

Use the orbit you scrubbed. For each hemisphere at each point, tick every property that is true, then check your grid.

North, when the north leans in
South, at that same moment
North, when the south leans in
South, at that same moment
Either hemisphere, at an in-between point

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

Why it can be summer in one half of the world and winter in the other — at the very same moment.

What you need to know

  • Earth spins on an axis — an imaginary line through the North and South Poles — and that axis is tilted compared with the flat plane of Earth's orbit round the Sun.
  • One complete orbit of the Sun takes one year, and all the way round, the axis keeps pointing in the same direction in space.
  • So for part of the year the Northern Hemisphere is tilted towards the Sun, and for the opposite part of the year the Southern Hemisphere is.
  • The hemisphere tilted towards the Sun has summer; the hemisphere tilted away has winter — so north and south always have opposite seasons.

The big picture

Earth's spin axis is tilted, and it keeps pointing the same way in space as Earth makes its year-long trip round the Sun. So for part of the year the Northern Hemisphere leans towards the Sun, and for the opposite part the Southern Hemisphere does. The half leaning in gets summer: a high Sun, days longer than nights, and direct sunlight that packs its energy into a smaller area. The half leaning away gets winter. In between, day and night are roughly equal everywhere — and the two hemispheres always have opposite seasons, which distance can't explain.

Key points

1The tilt of Earth's axis causes the seasons, not changes in Earth's distance from the Sun.
2In summer the Sun is higher in the sky and days are longer than nights; in winter the Sun is lower and days are shorter than nights.
3Summer sunlight arrives more directly, so the same energy falls on a smaller area and heats the ground more; winter sunlight arrives at a shallow angle and is spread over a larger area.
4Each hemisphere has its longest days in summer and its shortest in winter.
5In spring and autumn neither hemisphere is tilted towards the Sun, and day and night are roughly equal in length everywhere.

Worked example

Problem

In the UK (Northern Hemisphere) it is the middle of winter. A friend lives in New Zealand, in the Southern Hemisphere. Describe what your friend's day is like — the season, the height of the Sun and the length of the day — and explain why.

⚠ Watch out

Saying summer happens because Earth is closer to the Sun. At any moment both hemispheres are practically the same distance from the Sun, yet one has summer and the other winter — only the tilt can explain that.

🧠

Memory hook

Lean in, summer's in. The half of Earth leaning towards the Sun gets the high Sun, the long days and the warmth — and the axis never changes where it points; Earth just carries it round the Sun.

✓

Check yourself

A hemisphere is tilted away from the Sun. Without looking back, say its season, how high the Sun climbs, how long its days are, and why its ground heats less.

Flashcards

(13)
What causes Earth's seasons?
The tilt of Earth's axis — not changes in Earth's distance from the Sun.
What is Earth's axis?
The imaginary line through the North and South Poles that Earth spins around.
Earth's axis is tilted compared with what?
The plane of Earth's orbit around the Sun.
How long does Earth take to orbit the Sun once?
One year.
As Earth orbits the Sun, does its axis change direction?
No — it keeps pointing in the same direction in space all year.
Which hemisphere has summer?
The one tilted towards the Sun.
How does the Sun's height in the sky differ between summer and winter?
It climbs higher in summer and stays lower in winter.
When does a hemisphere have its longest and shortest days?
Longest days in summer (days longer than nights); shortest in winter (days shorter than nights).
Why does direct sunlight heat the ground more?
The same energy falls on a smaller area, so each bit of ground gets more of it.
What happens to sunlight arriving at a shallow angle?
Its energy is spread over a larger area, so it heats the ground less.
When the Northern Hemisphere has summer, what does the Southern Hemisphere have?
Winter — the two hemispheres always have opposite seasons.
What is special about day length in spring and autumn?
Neither hemisphere is tilted towards the Sun, so day and night are roughly equal everywhere.
What fact rules out distance as the cause of the seasons?
Both hemispheres are practically the same distance from the Sun at any moment, yet they have opposite seasons.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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How this lesson was checked. This KS3 Physicslesson was published through Lightbulb Learning's human-designed editorial process — the educational standards, accuracy rules and publication checks it must pass were authored and approved by Philip Halpin. It passed subject-specific assessment, automated educational checks and technical publication verification before going live (publication checks completed 1 October 2026). Published pages are monitored, human spot-checking is ongoing across the lesson library, and anything found wrong is corrected or withdrawn. How our lessons are made and checked. Spotted a mistake? Email hello@lightbulblearning.co and we'll review it.