Although the Sun is more than 100 times larger than Earth, it is also a very long way away—about 93 million miles (150 million km). At this distance it appears quite small in the sky. It radiates heat and light in all directions, but because of the distance, most of its radiation misses Earth altogether. As the diagram shows, we receive only a small fraction of it, and the radiation that we do receive falls only on the area of the surface directly facing the Sun. Some places are exposed to more intense sunlight than others and, because the Sun radiates heat as well as light, that is why they have warmer climates.
Imagine a huge disk with the Sun at its center and the Earth traveling around the edge, so that the edge marks the path of the Earth's orbit. This disk is known as the plane of the ecliptic. At noon, a person standing at a point where the plane of the ecliptic intersects the surface will see the Sun directly overhead. That point rests on a line marking a circle around the Earth, and the closer you are to that line, the warmer and sunnier the climate is likely to be—or would be if the solar energy did not produce such a large amount of cloud and rain.
Solar radiation. Because of the distance between the Sun and Earth, most of the Sun's radiation misses us.
Seasons and Tropics
axis of rotation (tilted about 23.5°)
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