This should allow you to animate your scene without looking odd. It provides a constant sky so you can do your animation. Mess with it until it's perfect for you.

If you need more help let me know!

OH and this was only to give the idea of how to do it. I'm sure the size of the terrain and sphere will turn out different for you! And i'm sure your going to make it look like more of a desert I only did this to show you the path to how to do it. Hope it helps!!!