what causes the sun to appear deep orange or red at sunset?

Answer 1

Monica's answer points to a website that gives the right answer, but here is a shorter explanation:

It's the same thing that makes the sky blue.
The earth's atmosphere tends to bend the sun's light, but it does not bend all of the frequencies (all of the different colors) by the same amount. The blue frequencies (and frequencies close to blue) are bent the most. That's why you can see blue coming at you from every direction during the day; it's light from the sun that wasn't beamed directly toward you, but was refracted (bent) by the earth's atmosphere.

So what about the colors farthest from blue? The reds and oranges are bent the least, so the light coming directly at us has more red and orange, and less of the blue light (whose rays were refracted away and made the sky blue for other locations on earth).

When the sun is high in the sky, we don't notice that it is a little more red/orange and a little less blue than what we think of as "sunlight." But, when the sun is setting and is low in the sky, its light passes through more of the atmosphere before reaching our eyes. As a result, it has more opportunity to lose its blue rays to refraction, and the light rays that make it all the way through all that atmosphere are mostly red and orange. Thus the reddish-orange setting sun.

Answer 2

It's called air pollution. Basically the light spectrum gets diffused by the dust particles.

Answer 3

It is being viewed through a greater amount of the Earth's atmosphere and all of the crud in it.

Answer 4

I always thought it was pollution, but this gov't weather guy says it's not ...

http://www.spc.noaa.gov/publications/corfidi/sunset/

Answer 5

usually the atmosphere and where you are..if there's a lot of lights around and what's in the air...

Answer 6

diffraction of light by particulates in the atmosphere

Answer 7

Pollution , sand and dust .