Crepuscular rays are bands of
sunlight which shine through breaks in a
cloud formation. These rays diffuse through
haze,
rain,
snow, or
dust in the
air to make visible contrasting bands of
light and/or
shadows in mid-air.
One of the most interesting pictures of crepuscular rays which I have seen recently was an astronomy picture of the day during a space shuttle launch at sunset with a full moon. Although this was caused by a man-made event, it is still very interesting.
http://antwrp.gsfc.nasa.gov/apod/ap010219.html
There is a more stereotypical picture as well as an in-depth description of crepuscular rays at
http://www.ems.psu.edu/~demark/471/CrepuscularRays.html
These are also very common elements of religous artwork.