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Seasons
Factfile |
 Seasons |
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What Causes Seasons ? |
The Earth also moves around the Sun along its orbit (path). Over thousands of years the shape of the Earth's orbit varies, but because the orbit is not quite circular, the Earth is closer to the Sun at certain times of the year than others. It takes a year for the Earth to complete its orbit.
However, as the Earth is moves round the Sun, spinning on its axis, it may surprise you to know that the Earth's axis is at an angle - a tilt of 23.5º from the vertical and It is this tilt that causes the changing seasons that we experience. If one hemisphere is tilted towards the Sun, the other is tilted away.
The Yearly Orbit of the Earth around the Sun
For example, when the northern hemisphere is tilted towards the sun, it is summer in the north. The sun is then higher in the sky than it is in the winter, so it spends more time above the horizon and the days are longer. The Sun's rays are also concentrated over a short area, so their heating effect is more. (Meanwhile, it is winter in the southern hemisphere as it is tilted away from the Sun).
Near the Poles, summer is never hot - but it is warmer than winter. The Sun's rays are not hot enough to melt the polar ice caps as the sun is very low in the sky, so its rays are spread over a wide surface making the Poles cold throughout the year.
In the tropics (the broad zone at the Equator - the world's hottest region) there are no real seasons in places like the Sahara desert, as the weather hardly changes over time. However, there can be two seasons in the year - one wet and one dry - which is typical of the tropical climate that can be found in most of India.
But what causes autumn and spring?
Between the poles and the tropics are the Earth's temperate regions. Temperate means mild or moderate and these places experience seasons, which change gradually. If you think about the weather in somewhere like Europe, which is classed, as temperate, the seasons slowly change from winter to spring, when the days start to get warmer. When spring is over, summer follows with lots of sunshine. Cooler weather starts to return in the autumn and then the weather finally changes to winter again.
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