Why the moon is red-orange sometimes?
It is the same reason that the sun is red at sunset and sunrise. Blue light is
scattered more strongly by haze, soot, and other aerosols than red light is, so
if there is haze, etc. in the air the red light will come through more strongly.
Note that this effect is strongest when the moon is nearest the horizon, when the
moonlight has to pass through a greater thickness of air.
The moon is also red during lunar eclipses. This is because the only light that
reaches it has passed through the edges of the earth's atmosphere.
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Update: June 2012