smoothing out shadow

[gib65]

Hello,

I'm wondering if there's a way to smooth out shadows. I have a few buildings and the shadows cast by the light are very choppy. They almost look like steps. Is there any way to smooth them out into straight lines?

Here's a diagram to show you what I mean:

http://www.shahspace.com/fig11.jpg

The one on the left is what it looks like now. The one on the right is what I'd like it to look like.

Thanks for any forthcoming help.