The Sun and stars all appear to travel across the sky because the Earth is spinning on its axis. They appear to travel in circles around a fixed point in the sky which, in the northern hemisphere, is called the North Celestial Pole. Since the stars don't appear to move relative to one another in the sky, whenever they can be seen or photographed, they always follow the same circles across the sky: some large, some small.
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photo by Gene Steeves |
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The Sun is different though. Because of the Earth's orbit around the Sun and because of the tilt of the Earth's axis in space, the Sun appears at different positions in the sky at different times in the year. The circle it follows during the day therefore depends on the time of year. In summer the circle is large and the Sun is in the sky for many more hours than it is in winter.
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So you can see that, in summer, not only is the sunlight spread over a smaller area, but the Sun is in the sky for longer each day. Both these effects help make summer warmer than winter. |
