MARK GARLICK / SCIENCE PHOTO LIBRARY MARK GARLICK / SCIENCE PHOTO LIBRARY
Earth's orbit showing seasons. Computer diagram of the Earth's orbit around the Sun, showing how the planet's tilted axis gives rise to the seasons. Each hemisphere experiences winter when it is pointed away from the Sun, and summer when it is pointed towards the Sun. From top, clockwise, the seasons shown are (for the northern hemisphere), spring, summer, autumn and winter.
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