Near the horizon sunlight passes through thicker layers of air having larger particles that scatter light of longer wavelength such as the red end of the spectrum. Also it travels larger distance at horizon before reaching the earth. However, light from the Sun overhead travels relatively shorter distance. At noon, the Sun appears white as only a little of the blue color is scattered whereas, near the horizon, most of the light of shorter wavelength at the blue end of the spectrum are scattered away by the small particles of the atmosphere. Therefore, the light that reaches our eyes is of longer wavelength which gives rise to the reddish appearance of the Sun.