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Atmosphere and sunlight

The effects of atmosphere on the sun's light


Spectacular sunset colors are due to the increased amount of atmosphere that the sun's rays must travel through
Spectacular sunset colors are due to the increased amount of atmosphere that the sun's rays must travel through

THE ATMOSPHERE SCREENS OUT WAVELENGTHS IN VARYING DEGREES

The Earth’s atmosphere screens out most of the sun’s wavelengths that are shorter than those of visible light by absorbing them when the short wavelengths strike atmospheric molecules. The shortest of the invisible sun’s rays that get through the atmosphere and that can affect ordinary films are those of the ultraviolet group.

Other wavelengths get through the atmosphere in varying degrees dependent on the amount of moisture, smoke, dust, clouds, carbon dioxide and even the angle at which the sun’s light strikes the Earth which is dependent upon the seasons and the time of day. More or less light waves get through under different atmospheric conditions, and it is this variance (which rays are or are not blocked by the atmosphere) that results in, for example, the different colors of the sky and clouds at noon or at sunset.

SCREENING IS MORE OR LESS AT DIFFERENT TIMES OF DAY

The sun’s rays have a greater distance to travel through the Earth’s atmosphere at sunrise and sunset than they do when the sun is directly overhead at noon. Longer rays (reds and greens) tend to penetrate the atmosphere more readily than shorter rays (blues), which the atmosphere more easily scatters. This is why the sun looks to us to be yellow, because as we saw earlier, a combination of red and green waves produces yellow.

SCREENING IS GREATEST AT SUNRISE AND SUNSET

At sunset, the sun becomes more reddish because its rays have to pass through more atmospheric molecules, so proportionately more scattering of green and blue wavelengths occurs while more longer wavelengths (red) penetrate. The color of the sun then appears more reddish and its “warmer” light paints clouds, smoke particles and atmospheric dust to give us spectacular sunsets. (See our tips and hints section on Photographing Sunsets.)

The quality of light changes throughout the day. When the sun is low on the horizon, light becomes
The quality of light changes throughout the day. When the sun is low on the horizon, light becomes "warmer," resulting in illumination like this.

LIGHT'S QUALITY IS DETERMINED BY THE SUN'S POSITION

The quality of overall light changes too when the sun is low on the horizon because more of the sun’s rays have been scattered by the relatively-increased amount of atmosphere the light must travel through. The light captured by the sky illuminates shadow areas, softening contrast, giving us that pleasant overall illumination known as “photographer’s light” that can produce such beautiful and delicate portraits and pleasant scenes.

Invisible longer wavelengths that can penetrate the Earth’s atmosphere include infrared, which are longer than the most intense visible red wavelengths and can be detected by special infrared film. (See our section on Infrared film for tips and hints for its special applications.)

Beautiful sunsets are due to the increased amount of atmosphere the sun's light must travel through, and also sometimes due to smoke and other pollutants in the air.
Beautiful sunsets are due to the increased amount of atmosphere the sun's light must travel through, and also sometimes due to smoke and other pollutants in the air.

 
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Infrared film