Why do we have seasons?
Not because Earth gets closer to the Sun. The tilt of Earth's axis does it, and a 10-year-old can see how with a lamp and a ball.
The idea
Earth's axis is tilted by about 23.4°, and it stays pointed the same way in space all year. So as Earth goes round the Sun, for half the year the northern half leans towards the Sun, and for the other half the southern half does. The half that leans in gets sunlight more straight-on and longer days: that's summer. The other half gets slanted light and short days: winter. Both happen at the same time, one in each half.
Where kids get stuck
- Most people, adults too, think summer is when Earth is closest to the Sun. It isn't: Earth is closest in early January, in the middle of the northern winter.
- Distance can't explain why Australia has summer while Canada has winter. Tilt can, and that's the test of whether the idea has landed.
Try it at home
A lamp for the Sun and a ball with a knitting needle through it at a slant for Earth. Walk the ball round the lamp, keeping the needle pointed at the same wall the whole way. Watch which half faces the lamp. Then shine a torch straight down on a sheet of paper, and again at a slant: the slanted patch is bigger and dimmer. That is winter light.