Tyler- Nice question. The reason is that the sky is blue. That's also
why the Sun changes color when it rises or sets, compared to when it's
overhead.
So how does that work? The molecules in air scatter blue light more
than red light. That's why when you look at the sky in the day, you see
mainly blue, because that's the type of light that bounces around most
and comes in from all over the sky. When the Sun or Moon is straight
overhead, the light goes straight through the atmosphere, and not too
much is scattered. So when you look at the Moon you see a color close
to the white color of the light reflected by the Moon.
When the Moon is near the horizon, the light from it travels
close to the surface of the Earth for a long way, so it travels through
much more air than when it's overhead. More blue light gets scattered
away. That leaves mostly redish-yellow light coming straight from the
moon.
Mike W.
p.s. If you're wondering why the air molecules scatter blue light
the most, we can try to answer that too, but the answer is not so
simple.
(published on 10/22/2007)
