The lighting/shadows situation is a little weird

[mramato]

I don't have a great solution, but I wanted to write an issue to start a discussion regarding our current lighting/shadow situation.

1. If you have lighting on and zoom in to the dark side of the earth, the lighting fades out when you get close to the ground. (I like this behavior).
2. If you have lighting on and terrain with normal lighting on, the lighting stays dark when you zoom in. (otherwise I guess the terrain would end up not lit at all)
3. If I have shadows on, but lighting off it still acts as if lighting is on except that the atmosphere is still drawn on the dark side of the world.

Perhaps having shadows on should force lighting on, that would get rid of 3? The current mix of behavior is kind of confusing from an end-user point of view. Perhaps an enum would help here, I'm not sure.

[pjcozzi]

CC #2594