Graphics Light shines through backside of ground

While checking out the cool new sky, I rotated the sun light under the ground and saw this. You get a sort of eclipse effect appearing to light up the ground from underneath it. I'm not sure if this is really an issue or not. If it's night time you probably shouldn't have a sun anywhere in the scene.

 

Come to think of it, this might just be the material I was using. It might have alpha or something that's letting the light shine through. I tried another material and it didn't do that.

Feel free to delete this thread if it turns out to be pointless clutter.