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Q & A: Moon rise

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Most recent answer: 10/22/2007
Q:
Why is there a difference in the color of the moon as it rises and when it is overhead?
- tyler (age 17)
coshocton,Ohio,USA
A:
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)

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