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Photographer's Note

Light from the sky is a result of the scattering of sunlight, which results in a blue color perceived by the human eye. On a sunny day Rayleigh scattering gives the sky a blue gradient — dark in the zenith, light near the horizon. Light that comes in from overhead encounters 1/38th of the air mass that light coming along a horizon path encounters. So, fewer particles scatter the zenith sunbeam, and therefore the light remains a darker blue.

The blueness is at the horizon because the blue light coming from great distances is also preferentially scattered. This results in a red shift of the far lightsources that is compensated by the blue hue of the scattered light in the line of sight. In other words, the red light scatters also; if it does so at a point a great distance from the observer it has a much higher chance of reaching the observer than blue light. At distances nearing infinity the scattered light is therefore white. Far away clouds or snowy mountaintops will seem yellow for that reason; that effect is not obvious on clear days, but very pronounced when clouds are covering the line of sight reducing the blue hue from scattered sunlight. This can be observed at the bottom part of the picture on top of the article.

The sky can turn a multitude of colors such as red, orange, purple and yellow (especially near sunset or sunrise) and black at night. Scattering effects also partially polarize light from the sky, most pronounced at an angle 90° from the sun.

Sky luminance distribution models have been recommended by the International Commission on Illumination (CIE) for the design of daylighting schemes. Recent developments relate to “all sky models” for modelling sky luminance under weather conditions ranging from clear sky to overcast.
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source: wikipedia

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Additional Photos by Daniel Draghici (dkmurphys) Gold Star Critiquer/Gold Star Workshop Editor/Gold Note Writer [C: 5845 W: 83 N: 11973] (79107)
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