|MadSci Network: Environment & Ecology|
Rays of light from the sun do not only follow a linear path to the earth's surface. If they did, the sky would not be blue and the sun would not look yellow or red. First of all, light spreads out in a cone from a point source. The sun consists of many point sources and therefore generates many cones of light, including the invisible UV, before it approaches the earth's atmosphere. Light is scattered by particles in the atmosphere, so that the rays do not just strike the earth on a straight line path from a point on the sun, but are scattered into all directions. To understand this analysis, it is not enough to know some geometry of the sun and the earth's orientation throughout the year. One also needs to understand the physics of light transmission and of scattering.
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