Wx Savvy | Science

Why Is The Sky Red At Sunset & Sunrise?

During a sunset, light travels through more atmosphere. In the diagram, notice how much longer the path of light is at sunset. Thus, as the light travels through more atmosphere, the light is subjected to more and more gas molecules in the air.

The result is that the blue light is removed by scattering (see why the sky is blue). Normally the air scatters the blue colors of light. But with such a longer path for the light to take to get to our eyes, all of the blue, indigo and violet are scattered out.

The colors that are not scattered and do reach our eyes are red, orange and yellow.

When the blue has been scattered out, even the clouds which usually scatter all colors and thus look white, actually appear red too. That's because the only color the clouds can reflect, is the color that shines on it. If blue is scattered out, only red will be reflected and scattered off of the clouds and into your eyes.

In space the sky appears black because space has no atmosphere to scatter the blue color. In fact, there's no atmosphere in space to scatter any colors, hence it appears black.

Why is the sun yellow? Although the sun emits all colors, it peaks in the yellow range(1). Different stars peak in different color ranges depending upon their temperature (2).

Picture: http://scifun.chem.wisc.edu/HOMEEXPTS/BlueSky.htm

(1) http://www.madsci.org/posts/archives/dec99/945169710.As.r.html

(2) http://zebu.uoregon.edu/~soper/Stars/color.html