A tilted planet
Why Do Seasons Change?
Earth leans over. That lean, not our distance from the Sun, makes summer and winter.
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Step 1 of 5
It is not about being closer to the Sun.
Almost everyone guesses summer is when Earth is nearest the Sun. It is not. Earth is actually slightly closest in January, in the middle of northern winter.
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Step 2 of 5
Earth leans to one side.
Our planet's axis is tipped about 23 degrees, and it keeps pointing the same way all year — like a spinning top leaning as it goes round.
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Step 3 of 5
The leaning half gets steeper sunlight.
When your half leans toward the Sun, the rays come down steeply and land concentrated on a small patch of ground. That patch heats up fast.
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Step 4 of 5
The leaning half also gets longer days.
Tilting toward the Sun swings your part of Earth through more of the lit half each spin. More hours of sun on top of stronger sun makes summer.
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Step 5 of 5
So the two halves swap.
When the north leans in, the south leans out. That is why Australia has Christmas in summer while Canada has snow.
At the poles the tilt is so extreme that the Sun does not set for weeks in summer, or rise for weeks in winter.
The short version
Seasons come from Earth's lean, which changes how steeply the sunlight lands and how long it lasts.
Try it yourself
Shine a torch straight down onto paper, then tilt the paper. Watch the bright circle stretch into a dim oval — that is winter.
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