The seasons


The tilt of the Earth
This diagram shows how the Earth moves round the Sun in its orbit. Notice that no matter where the Earth is in its orbit it remains tilted in the same direction. During the year the tilt affects the amount of sunshine that each place on the planet receives.

When the Northern Hemisphere tilts towards the Sun, the Sun stays longer and rises higher in the sky. At the same time the Southern Hemisphere tilts away from the Sun, so the Sun stays in the sky for a shorter time and is lower in the sky. Six months later, when the Earth has moved in its orbit, the conditions are reversed.

Why does sunlight make it warm?
The rays from the Sun contain both light and heat. We see the light but it does not make us warm. It is the heat, which comes with the light, that makes us warm.
When rays of heat travel away from a hot object they spread out and heat a place less strongly. If the Earth were nearer the Sun it would receive more heat and the planet would be too hot for living things to survive. If the Earth was further away from the Sun it would receive less heat and would be too cold for living things to survive.

Why are the Sun's rays hotter in summer than winter?
In summer, when the Earth tilts towards the Sun, the Sun's rays heat a smaller area on the planet than in winter, just as rays light a smaller area more brightly. Try the planet orange test again and this time imagine that the spot of light is really heat and you will see the change.



What is a season?
It is a time of year when a place has a certain type of weather for a few months. For example, in winter there are months of cold wet weather with frost and snow.

What causes the seasons?
The main cause of the seasons is the tilt of the Earth. It changes the amount of sunshine which reaches most parts of the Earth.

Is it summer everywhere at the same time?
No. When it is summer in one hemisphere, it is winter in the other hemisphere. This is because their part of the Earth is tilted away from the Sun. When one hemisphere is tilted towards the Sun it will be summer there, and winter in the other hemisphere because it will then be tilted away from the Sun.
Do all places have four seasons?
No. Places near the equator such as tropical grasslands and rainforests are not affected by the tilt of the Earth and stay warm all year. However, instead of having changes in heat, they have changes in rainfall. Many tropical places have wet and dry seasons.

Do all planets tilt like the Earth?
No. Each one has a different angle of tilt . Here are the angles of tilt of all the planets in the Solar System Mercury 0°, Venus 2°, the Earth 27°, Mars 25°, Jupiter 3°, Saturn 26°, Uranus 97°, Neptune 28°, Pluto 62°.