Smog Creates Beautiful Sunsets?

SunsetAccording to urban legend, air pollution enhances the beauty of a sunset. And pollution does indeed change the appearance of sundown, but whether it tips it in the direction of beauty is a matter of personal taste—and the overall amount of that pollution in the air.

Be it the azure of high noon or the orange glow of dusk, the colors of the sky result from sunlight interacting with molecules in the air, primarily nitrogen and oxygen, which cause it to be deflected in all directions, a phenomenon called Rayleigh scattering. All wavelengths of light are scattered, but they are not scattered equally. According to John W. S. Rayleigh's approximate scattering law, colors with shorter wavelengths are scattered the most: violet, followed by blue, then green, and so on.

During the day, when the sun is directly overhead, light travels only a short distance through a relatively thinner section of the atmosphere. But as the sun edges toward the horizon, the light must travel increasingly longer paths and is scattered by more air molecules. By the time it reaches the end of this journey (our eyes), "most of the blue has been scattered out of that beam" explains Stephen Corfidi, a meteorologist at the National Oceanic & Atmospheric Administration (NOAA). What remains are the warmer hues of yellow, orange and red, which blend into a yellowish-orange sunset.

Yet, scattering by nitrogen and oxygen can only explain how sunsets can be orange and perhaps reddish, not how the sky can blush blood red. "In an atmosphere with no junk at anytime, you'll never get a sunset that would make someone with normal color vision say, 'Wow that's red!'" says Craig Bohren, professor emeritus of meteorology at Pennsylvania State University. "It is certainly true that the 'pollution' results in redder sunsets."

Read the full story after the jump.

Thanks, Scott !

Link & Image: Sciam
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