Red Lunar Eclipse

Why does the mood appear red during a lunar eclipse? Since the earth prevents the sun's rays to be reflected on the moon, should not the moon be black instead of red?
- Anonymous

During a full lunar eclipse, some light from the sun can still get to the moon if it bends a little going through the earth's atmosphere. Blue light tends to scatter a lot in the atmosphere, changing direction a big amount. That's why on a clear day you see blue light coming in from all directions, i.e. the sky is blue. The red part of the sun's light scatters some also, but not as much. It seems that the light that has changed directions a bit, but not a lot, is mostly that red light. So the moon looks red in a lunar eclipse.

Mike W.

(published on 12/19/2010)