I'm not sure what's happening out there in the universe, but since the Bill Nye/Ken Ham debate, this question seems to be popping up more frequently.
I regularly update and maintain my pet project, Atheist FAQ, and have a mechanism for anonymous feedback (which I mostly get pharmaceutical promotions through), and the above question landed in my inbox.
I'm not sure - is this a real question?
Go outside, when it's early morning or late evening, where you can see the sun. Pretend your head is the Earth, where you're looking outwards, and twirl around. Note how the sun appears to "rise" on one side and "set" on the other.
Where, exactly, does God enter the equation? If this question is serious, I'm not sure the person would understand the answer.
I have a blanket response to the "If there is no God, how do you explain ____?" questions. Maybe he/she just didn't read that far? In this case, the answer is not "we don't know".