Space shuttle crews see a sunrise or sunset every 45 minutes
as they circle the Earth at 27,300 kilometers (17,000 miles) per
hour, crossing the surface at 6.4 kilometers (4 miles) per second.
From their unique perspective they see clearly defined bands of
color through the atmosphere as the sun rises. High-peaking cumulus
clouds, topping out in anvil-head cirrus can be seen as black
shadows against the sunlit horizon. The brightness of the colors
in the atmosphere in this photograph taken over the South China
Sea is due to concentrations of dust in the atmosphere. Greater
concentrations of dust are found in equatorial regions. There
are various sources for such upper level dust. Many dust storms
in Africa, intensified by several years of drought, have been
responsible for putting large amounts of dust into the atmosphere
in recent times. Ash clouds from major volcanic eruptions can
have a similar effect. Recent discussion of the climatic and environmental
effects of a "nuclear winter" centering on upper atmosphere
pollution has drawn from the atmospheric effects of catastrophic
volcanic eruptions (Courtesy LPI/NASA)