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llustration showing Earth's orbit of the Sun. The Earth is the third planet from the Sun, with an average distance from it of about 150 million kilometres. It takes just over 365 days to orbit the Sun and just under 24 hours to rotate around its own axis. Its axis of rotation is tilted to the plane of its orbit by 23 degrees, giving rise to the seasons. Each hemisphere experiences winter when it is tilted away from the Sun, and summer when it is tilted towards the Sun. For a labelled version of this image see C058/0999. (KEYSTONE/SCIENCE PHOTO LIBRARY/CARLOS CLARIVAN)