Why Does the World Change Four Times a Year?

Imagine waking up one morning and the trees outside are bare and dark. Six months later you look out and those same trees are bursting with green leaves and bright flowers. What made them change? The answer is seasons — and they are caused by something happening millions of kilometres away in space.

Earth travels around the Sun once every year. As it travels, it is slightly tilted to one side — always pointing the same way, like a spinning top that leans. This tilt is the key to seasons. When your part of Earth tilts TOWARDS the Sun, the Sun sits higher in the sky. Its light is stronger and the days are longer. This is SUMMER. You feel warm, plants grow fast, and it stays light late into the evening. Six months later, your part of Earth tilts AWAY from the Sun. The Sun sits low in the sky. Its light is weaker and the days are shorter. This is WINTER. Temperatures drop, many plants stop growing, and it gets dark early. In between summer and winter we get two 'in-between' seasons. SPRING comes as your part of Earth moves back towards the Sun. Days grow longer, temperatures rise slowly, and plants begin to bud and blossom. AUTUMN (also called fall) comes as your part of Earth tilts away again. Days shorten, temperatures cool, and the leaves on many trees turn orange and red before falling. Here is an important point: when it is summer in the northern half of the world (for example, the UK or Canada), it is winter in the southern half (for example, Australia or South Africa). The tilt works in opposite directions for opposite halves at the same time. The order of seasons in the northern half is: Spring → Summer → Autumn → Winter → Spring again.