Why sun looks reddish at sunset and sunrise.

 We all know that, the light of sun consists of a seven colours in it. They all are of different wavelength and frequencies. 

When Sun is at horizon of earth. i. e at morning and at evening. At that situation the light coming out of the sun has to suffer a longer distance than at other positions. 

So, out of seven colours only red light has the maximum wavelength, which can travel a longer distance than other six colours. At horizon, when light ray from the sun emerges and enters into the earth's atmosphere then all the other ray except red, scattered into earth's atmosphere and only red light comes to our eyes. 

So, we see any objects in that colour when light that colour comes to our eyes. Since, only red light comes to our eyes,, so, we see sun in reddish. 

This is natural phenomenon.. we appears to be seen only at sunrise and sunset, due to longer distance... of sun's light and our eyes....