Scattering and Sun Altitude

As the sun nears the horizon the light passes through a much greater distance in the atmosphere. This increases the amount of blue light that is scattered out of the beam by molecules in the air.

With the sun almost 10 degrees above the horizon this cumulus cloud rising into clear air appears clean and white.

Two hours later the sun is more than a degree below the local horizon. This cumulus cloud is now catching sunlight that is heavily reddened by the much longer passage through the atmosphere.

Canon EOS 5D   10th April 2012
Wiltshire, England

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