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Sunset, also called
sundown in some American English dialects, is the time at which
the Sun disappears below the horizon in the west. It should not
be confused with dusk, which is the (variously defined) point
at which darkness falls, some time after the Sun itself sets (which
begins twilight). The red hues of the sky at sunset are caused
by the Rayleigh scattering of blue light by atmospheric dust.
Relatively little red light is scattered in this way, and so the
sky often takes on shades of red, orange and yellow. The color
of a sunset may be enhanced by atmospheric phenomena such as clouds,
smoke and smog produced by natural processes or human activity,
and by ash from volcanic eruptions. A number of eruptions in recent
times, such as those of Mount Pinatubo in 1991 and Krakatoa in
1883, have been sufficiently large to produce remarkable sunsets
(and sunrises) all over the world.
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The sunset is often more brightly coloured than the sunrise. The
atmosphere responds in a number of ways to expsure to the Sun
during daylight hours. In particular, there tends to be more dust
in the lower atmosphere at the end of the day than at the beginning.
During the day, the Sun heats the surface of the Earth, lowering
the relative humidity and increasing wind speed and turbulence,
which serves to lift dust into the air. However, differences between
sunrise and sunset may in some cases depend more on the geographical
particulars of the location from which they are viewed. For example,
on an west-facing coastline, sunset occurs over water while sunrise
occurs over land.
Above Images Are From The NOAA
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