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Transcript: The seasons are caused by the tilt of the Earth’s spin axis as it orbits the Sun. If there were no tilt of the axis there would be no seasons because the illumination at every point on the Earth’s surface would not vary throughout the year. In the winter in the Northern Hemisphere, the Northern pole of the Earth tips away from the Sun. So Northern parts of the Earth receive less direct sunlight, and the day is shorter than twelve hours. In the Northern Hemisphere summer, the Northern pole of the Earth tips towards the Sun. The day is longer than twelve hours, and Northern parts of the Earth’s surface receive more direct sunlight and therefore more heating. The cause of the seasons is entirely this tilt. Many people think that the seasons are caused by the changing Earth-Sun distance. Not true. This effect is very small, only a few percent, and in any case it could not possibly explain the fact that the Southern Hemisphere experiences the opposite seasons to our seasons in the Northern Hemisphere.
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