what happen to the refraction of air as the sun sinks lower on the horizon?

Answer 1

Sunlight bends toward the earth as the sun sinks lower on the horizon. This phenomenon occurs for two reasons, one since the earth's atmosphere is like a convex lens and another since the air is denser near the earth's surface. Sunlight bends before it reaches you and bends even further as the sun sinks on the horizon. For this reason, you will still be able to see the sun after it is physically below the horizon (along with another factor in that it takes eight minutes for sunlight to reach the earth anyway.)

To better understand what happens with the increasing air density near the earth, it may be useful to understand how fiber optic strands are constructed. Modern fiber optics use the principle of a density gradient. The refractive index is higher near the center of the fiber optic strand and gradually decreases toward the outside edge. Light traveling down the strand which starts to stray toward the edge of the strand will move toward an area of lower refractive indexes and be refracted back toward the center. Older fiber optic strands were a uniform density and light traveling down the strand simply bounced back toward the center once it hit the side of the strand. This made for some variation in the time it took for light to travel down the strand and a light pulse wasn't as clean as it is today with modern fiber optics. If our atmosphere was uniform, sunlight would bend once when it hit the atmosphere and would travel in a straight line until it either hit the earth or exited the atmophere.

Answer 2

The refraction (and dispersion) of the atmosphere remain relatively constant. But, as teh Sun goes to the horizon, the path length through the atmosphere increases quite a bit. This causes most of the refracted rays observed to be towards the longer wavelengths (the 'red' end of the spectrum)


Doug

Answer 3

It increases because there is much more of it between Earth and the sun at dusk. Hence the "large sun" at sunset.