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The seasons change because the tilt of Earth's axis causes places on the planet to receive different amounts of sunlight during the year. When the North Pole has its greatest slant toward the sun, summer begins in the Northern Hemisphere, left. The sun's rays strike Earth from a high angle, and northern areas receive maximum sunlight. When the pole has its greatest tilt away from the sun, winter begins in the Northern Hemisphere, right. The rays come from a low angle, supplying minimum light. As Earth moves halfway between these positions, autumn and spring begin.

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