On clear days the sky appears blue. However, on hazy, foggy, or cloudy days the sky appears white. Why the difference?

Kainantu

...the sun will degenerate into a white dwarf, at which point its energy output will drop steadily until it becomes a black dwarf, giving off no energy. Though neither will occur for billions of years to come, these two events will put a serious damper on the blueness of the sky. Realistically, we are having the greater effect on color changes. The sky is whiter with increased dust content, and other pollution makes it both whiter and more like the color of the pollution. . . . Small particles like molecules scatter a larger proportion of the short-wave radiation, the blue and violet light, than the longer-wave yellow and red light. That is the reason the sky is blue in the absence of haze or smog. Haze, fog, and smog contain larger particles, which scatter more nearly equally in all wavelengths. When they are present, the sky tends to be white, particularly near the horizon, except when smog with absorptive properties gives it a yellow or brownish color. (Neiburger 56) - Neiburger, Morris, et al. Understanding Our Atmospheric Environment. San Francisco: W.H. Freeman and Company http://www.cise.ufl.edu/~dcc/old/chris/whyblue.htm Dec 06 02, 8:21 AM