May 19, 2003
A: FROM MENTOR JOAN LUSK IN RI
As usual I wanted to check my answer, so I found
http://spacekids.broaddaylight.com/spacekids/FAQ_52_6639.shtm where it says
"Dark clouds aren't necessarily rain clouds. The water vapor, that
forms clouds, is dense enough to block out the sunlight and makes
clouds appear dark. If the clouds have enough water vapor in them and
certain other conditions are just right, then rain may fall." The
whiteness of clouds is scattered sunlight of all wavelengths,
reaching our eyes. When the clouds look black, obviously much less
light is reaching our eyes. Where is it going? is it scattered back
into space? Is is scattered so many times that eventually it loses
energy and no longer is visible? I agree with you that it shouldn't
be _absorbed_ by clear raindrops (or ice crystals). I wasn't able
easily to find a good answer to that question - other articles on
light scattering by clouds were too technical for me.