Question

Why is the sky blue and clouds white on a clear day?

Answer 1

A clear cloudless day-time sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light.  When we look towards the sun at sunset, we see red and orange colour because the blue light has been scattered out and away from the line of sight.

Visible light comes at us in many different wavelengths, each corresponding to a slightly different color. When all the wavelengths combine, they show up as white light. White light may be a combination of wavelengths, but it's not a permanent combination of them. Under certain circumstances, wavelengths can be separated out. For example, earth's atmosphere tends to scatter blue light, while letting the other wavelengths of light pass through in a straight line. Because of this, the sky is blue – made up of diffuse, scattered light – while the sunlight that falls around us tends to be more golden, because the blue wavelengths of light have been filtered out. That's called Rayleigh scattering.

Clouds also scatter light. Unlike oxygen and nitrogen molecules, which are picky about which kind of light they scatter, larger water droplets scatter all kinds of light in all directions. This is called Mie Scattering. When we look up at clouds, we see red light, blue light, yellow and orange and green light, all coming at us. We can't see the individual colors, though, because since they're all coming at our eye from the same place. Together, they all combine - Power Ranger style - to make white light. That's what hits our eyes, and makes us perceive clouds as white.......