Blue Skies over Texas

from: Crawford Ranch

It's one of the questions that has plagued man since the beginning of time. Well, maybe not. It probably comes up in the minds of kids every once and a while though. The question is: Why is the sky blue?

The sky appears blue to us on a clear day, because the atoms of nitrogen and oxygen in the atmosphere separate the suns white light into its many colors, and scatter them throughout the atmosphere.

The wavelength of the blue light scatters better than the rest, predominates over the other colors in the light spectrum, and makes the sky appear blue to us.

The scientific name for this phenomenon is the Tyndall effect, more commonly known as Rayleigh scattering.

This phenomenon describes the way in which light physically scatters when it passes through particles in the earths atmosphere that are 1/10th in diameter of the color of the light. The light spectrum ranges in wavelength from red to violet, and, since the wavelength of the blue light passes through the particles with greater ease than the wavelengths of the other colors of light, the sky appear blue to the naked eye.

The human eye has three types of light receptors, known as cones, located in the retina. The cones are either considered to be red, or blue, or green, based upon their strong response to light at these wavelengths. As light stimulates these receptors, our vision translates the signals into the colors we see.

When gazing at the sky, the red cones respond to the small amounts of red light scattered, and even less strongly to the orange and yellow wavelengths. Although green cones respond to yellow, their response to scattered green and green-blue wavelengths is stronger. Finally, colors near the strongly scattered blue wavelengths stimulate the blue receptors.

In short, the skylight stimulates the red and green cones almost equally, while stimulating the blue cones more strongly. For these reasons, our vision naturally adjusts as clearly as possible to separate colors.



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