DAVID A. HARDY / SCIENCE PHOTO LIBRARY DAVID A. HARDY / SCIENCE PHOTO LIBRARY
Earth's orbit. Computer artwork showing the Earth revolving around the Sun. The Earth takes around 365 days to complete a full orbit of the Sun. The orbit is not perfectly circular, instead it is elliptical. The Earth is tilted on its axis (black line) as it rotates, and it is this that gives rise to the changing seasons. When the North Pole points away from the Sun (far right) it is winter in the northern hemisphere, and when it points towards the Sun (far left) it is summer in the northern hemisphere.
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