Science: July 2010 Archives

Why Are Clouds White?

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clouds2.jpgWhen you look at the sky on most days, you'll see a few clouds slowly drifting past, pushed by the wind. You might see the shape of a camel in one and a flower in another. You probably already know why clouds exist: water evaporates in the sunlight and rises into the sky, where it again forms tiny water droplets. When the droplets are too large to stay in the air, they fall to the ground as rain and the cycle begins again. But did you ever wonder why clouds are white, and why they become gray during a storm?

Katrianna wrote about why the sky is blue in a previous article, which explained how light is made up of many different colors. White light is a combination of all of the colors. Clouds are white because the water droplets or ice crystals (at a certain altitude, the water freezes to become ice) reflect all of the colors of light in a process called Mie scattering. (All of the colors are reflected in the same way, so they combine to become white light.)

Clouds are dark when they are so thick that the sunlight is blocked by the moisture. When you look down on dark clouds through an airplane window, the clouds will always look bright white. This is because the water or ice on the surface of the cloud is still reflecting the light. Thus, every cloud will have a silver lining -- if you view it from an airplane!

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This page is a archive of entries in the Science category from July 2010.

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