But how, exactly?
Well, the Eight Aedra orbit the Mundus as the Eight Planets, of definite form but infinite mass.
Nirn's moons, Masser and Secunda, are the flesh of Lorkhan.
Tiber achieved godhood by mantling Lorkhan.
Ergo, Tiber Septim is the moon.
This is obviously a ridiculous notion, but raises a very important question: Where is Talos?