Why Do We Have Seasons? The Real Reason (and the Myth Most People Believe)

Ask a room of adults why we have seasons and most will say, “In summer, Earth is closer to the Sun.” It sounds sensible, and it is wrong. Earth is actually closest to the Sun in early January, in the middle of Northern Hemisphere winter.

This is one of the most common science misconceptions, and fixing it makes a great lesson.

The real reason: tilt

Earth’s axis is tilted about 23.5° from the plane of its orbit. As Earth travels around the Sun, the tilt keeps pointing the same direction in space. That means:

For half the year, the Northern Hemisphere leans toward the Sun. Sunlight arrives more directly, and days are longer. That’s summer in the north.
For the other half, it leans away. Sunlight arrives at a lower angle, and days are shorter. That’s winter in the north.
The Southern Hemisphere is always the opposite. When Calgary has winter, Sydney has summer.

Why direct sunlight is warmer

Hold a flashlight straight at a wall and you get a small, bright circle. Tilt it and the same light spreads over a larger, dimmer oval. Sunlight works the same way. When the Sun is high in the sky, its energy lands on a small patch of ground. When it’s low, the same energy is spread out, so each square metre receives less.

Longer days add to the effect. More hours of sunlight means more time for the ground to heat up.

The evidence against the “closer” myth

Here are three ways to show that distance can’t be the cause:

Hemispheres. If distance caused seasons, the whole planet would have summer at once. Australia has summer in December.
The numbers. Earth is about 147 million km from the Sun in early January and about 152 million km in early July. That’s a difference of only about 3%, which is not enough to explain the temperature swing.
The data. Compare real monthly average temperatures from cities in both hemispheres against Earth’s distance from the Sun. The distance pattern doesn’t match the temperature pattern. The tilt pattern does.

Our lesson Is summer when Earth is closest to the Sun? has students test the myth this way, using real orbit distances and temperature averages from five cities in both hemispheres. Then they walk a human orbit with a tilted Earth to see the real reason.

Try this at home

You need a lamp with the shade off, a ball (an orange works), and a pencil or skewer pushed through as an axis.

Put the lamp in the middle of the room. That’s the Sun.
Tilt the ball’s axis toward a fixed spot in the room, such as a window. Keep it pointing there.
Walk the ball in a circle around the lamp, keeping the tilt direction the same.
Stop at four points. At each, look at which half of the ball is leaning toward the lamp.

Put a sticky note on your hometown. Watch how the light falls on it at each stop.

What about the equator?

Places near the equator get sunlight at a steep angle all year, so they have little temperature change. Many tropical regions have wet and dry seasons instead. Our lesson Why are there seasons and why do some places barely have them? covers this for younger students.

Common mix-ups to listen for

“Summer is when we’re closest.” Closest is in January.
“The tilt changes during the year.” The tilt stays the same. Our position in the orbit changes.
“It’s warmer because the Sun gets bigger.” It doesn’t. We can’t see any change in its size.

Keep exploring

These activities come from the Reason for the Seasons unit (Grades 5 to 8). Sign up to get three lessons free, or browse the library.