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COLORS IN THE SKY
Which ever way you look
at it, from space or here on Earth, the sky looks blue while clouds look white.
The reason for this is not because there are colorful pigments in the atmosphere,
but rather, it's due to the reaction of sunlight with air molecules. Sunlight
consists of white light which is a combination of all colors of the rainbow.
Light travels as waves and each color has its own unique wavelength. Light will
also travel in a straight line unless something sends it off it course.
As it turns out, air molecules
are just the right size to send the shorter wavelengths of light, mostly blue,
off in different directions. Longer wavelengths, like red, are not scattered
by air molecules. Therefore, as white sunlight enters the atmosphere, the blue
light is scattered and is spread all over the sky. Clouds are white because
their water droplets or ice crystals are big enough to scatter light of all
wavelengths, which combine to produce white light. Clouds may appear dark when
they're in the shadow of other clouds or surrounded by bright light.
Sometimes, additional air
molecules or lack of lead to differing sky colors. On hazy days, large numbers
of relatively large particles in the air make the sky white or gray. Larger
particles scatter more wavelengths of sunlight. Sunlight is white light made
up of all the colors in the rainbow. Pollution can make the sky look brown or
yellow because the particles are the right size to scatter those colors. When
the air is cold and dry, the sky takes on a deep blue hue because of the lack
of any large air molecules.
At sunrise or sunset, the sky turns red, orange or yellow because sunlight is
traveling through more air when the sun is low in the sky. The long path through
the air means most of the blue and other colors with shorter wavelengths have
been scattered out in different directions. Few reach your eye. You see the
yellow, orange, and red colors which pass more freely through the air. The most
vivid sunrises and sunsets, however, are brought by volcanoes and forest fires.
This is because the expelled particles are just the right size to scatter light
in the red end of spectrum.
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www.weather.gov 
