Why does the setting sun appear red ?

Explanation

As sunlight travels through the earths atmosphere, gets scattered by the large number of molecules present. This scattering of sun light is responsible for the colour of the sky, during sunrise and sunset etc.
The liht of shorter wave length is scattered much more than light of larger wave- length. `"Scattering "prop(1)/(lambda^(4))`
Most of blue light is scattered, hence the bluish colour of sky predominates.
At sunset (or) sunrise, sun rays must pass through a larger atmospheric distance. More of the blue colouris scattered away only red colour which is least scattered appears to come from sun. Hence it appears red.