Cool idea as the others have said! Really nice land shape too. The best bit is that you've worked out so much of the physics, though I just noticed one thing that doesn't seem right, even with magic; When the sun is rises and sinks, the equator would get the most extreme seasons, because it has the biggest variation in heat. The further away from the sun, the colder it will obviously be, but it will also be more even because the distance to the sun doesn't vary as much.