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Why Are Clouds White?

To understand why clouds are white we need to talk about color. What is color?

Color is light energy. Energy emitted in such a way that we can see it is called the "Visible Spectrum". There are other types of energy we can't see, like Infrared light energy or microwave energy.

The different levels of visible light energy all have different color. If all colors of the visible spectrum are present (Red, Orange, Yellow, Green, Blue, Indigo, Violet) then the color of light is white. If no light at all (not any of the colors above) are seen, then the color is called black.

White = all colors

Black = no colors

So, since clouds are typically white then clouds must reflect ALL colors of the rainbow, right?

You betcha.

 

And that is the simple answer to why clouds are white, because cloud particles happen to scatter and reflect all colors. For more on what's in a cloud, click here.

When all wavelengths or "parts" of light are scattered equally by a particle it is called Mie scattering. This type of scattering of all colors is different from the type of "selective scattering" responsible for the blue color of the sky. You can read more on why the sky is blue clicking here.

Now back to our discussion on cloud color, which is usually white. Some clouds however can appear different colors.

If the light hitting the clouds does not have all colors of light, then the clouds will scatter only the colors present in the light hitting the cloud. This may sound confusing, but it's easy to understand when you think of it like this; If you are shining a red light on a piece of paper the paper will look red. Why? Because the light hitting the paper is red to begin with.

Clouds, like the piece of paper, can act like a canvas for the reddish sunset sky. If you're curious as to how and why the sunset sky is red you can find out by clicking here.