Why does the Sun look reddish at the time of sunrise and sunset?

At sunrise or sunset,the Sun is near the horizon. The light from the Sun has to travel a larger distance through the Earth's atmosphere to reach our eyes.
During this journey,most of the blue light and other shorter wavelengths are scattered away by the atmospheric particles (Rayleigh scattering).
Only the light with longer wavelengths,such as red light,is able to reach our eyes as it is the least scattered.
Therefore,the Sun appears reddish at the time of sunrise and sunset.