Question

Draw a labelled diagram to show (i) reddish appearance of the sun at the sunrise or the sunset and (ii) white appearance of the sun at noon when it is overhead.

Answer 1

i) The reddish appearance of the sun at sunrise or sunset is due to the scattering of light by the molecules of air and other fine particles in the atmosphere that have the size smaller than the wavelength of visible light from the sun near the horizon. Light travels larger distances at the horizon in the earth's atmosphere before reaching our eyes and most of the blue light and shorter wavelengths are scattered away by the particles. So, only red light, being of higher wavelength reaches us which gives the reddish appearance of the sun at sunrise or sunset. 

ii) At noon, the sun appears white, not red, as only a little of the blue and violet colors are scattered because light from the Sun overhead would travel a relatively shorter distance.