sun angle and clouds

Hi,

I'd like to render a realistic scene with terrain shaded based on the
actual sun angle and a Alpha cloud that you can partially see that
terrain through.

1) How hard would it be to handle the sun angle effect?

2) Why can't I see a solid surface through an Alpha rendered field? What
is the potential for this to be corrected?

Thanks,
Doug

-- 
*----------------------------------------------------------------------*
| Doug Lindholm, Software Engineer          |  E-mail: lind@xxxxxxxx   |
| Research Applications Program             |   Phone: 303-497-8374    |
| National Center for Atmospheric Research  |                          |
| P.O. Box 3000                             |     There's no place     |
| Boulder, Colorado 80307-3000              |        like $HOME        |
*----------------------------------------------------------------------*