More cool but very basic mysteries of life you have wondered about...

Today, io-9 answers the question, "why are clouds white"? 

After all, we know that water droplets are transparant since we see them when they fall on us.

So, why are clouds - which are nothing but a whole bunch of water droplets - white?  Anyone?  Bueller?

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.

Rayleigh Scattering, check.  Mie Scattering, check. Sunlight is golden, check.  It's all good.