control sun position

Im making some tests with Caelum and everything goes well until I enable shadows. The problem seems to be that the sun is at the same level as terrain, thus some objects casts almost infinite shadows on the terrain. How can I make sure that the sun appear and disappear at a reasonable level above the "horizont"?

I am also having problems with this. My idea was to calculate the angle between the light and the horizontal and disable the shadows if too small or enable the shadows for the moon, instead.