 Most
of us who have ever cleaned a house would be much happier if
there were less dust.
However, without dust there would be less rainfall and sunsets
would be less beautiful.
Rain is formed when water molecules in the air collect around
particles of dust. When the collected water becomes heavy
enough the water droplet falls to the earth as rain. Thus
water vapor could be much less likely to turn to rain without
the dust particles.
The water vapor and dust particles also serve to reflect
the rays of the sun. At sunrise and sunset, when the sun is
below the horizon, the dust and water vapor molecules reflect
the longer, red, wavelengths of light such that we can see
them for more time (starting earlier in the case of sunrise
and lasting longer in the case of sunset) than any of the
other wavelengths. The more dust particles in the air the
more colorful the sunrise or sunset.
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