CLOUD COLORS -- The 8th graders in Sarah Gullett's class (Bedford, TX) wanted to know "why are some clouds gray and some clouds white?" -- 3/21/00

Clouds are quite reflective. If you fly over clouds and look down on them (or view clouds on visible satellite images), you will see just how white they can be. When viewed from Earth, the tops and sides of many clouds (cumulus especially) are very white. The whiteness is a measure of how much visible light (from all the colors of the spectrum) is being reflected.

The bottoms (and sometimes the sides) of clouds (most noticeable in cumulus type clouds) are varying shades of gray. This is because of shadowing. The cloud itself or clouds above it or to its side) block sunlight from reaching some parts of the cloud. The thicker the cloud (or the more cloud layers present), the more shadowing, and hence the darker the cloud. If the cloud bottom is almost black, the cloud is most likely a cumulonimbus or thunderstorm cloud.

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