Board Thread:Lore Discussion/@comment-14027812-20130913213949/@comment-24489208-20130914183933

From what I know, I think:

1. Well, we have the planets which orbit Nirn:

http://images4.wikia.nocookie.net/__cb20121124012635/elderscrolls/images/3/30/Dwemer_orrery.jpeg

We have the moons which orbits Nirn, we have the sun (Magnus) which seems to orbit Nirn and is an exit out in to Aetherius and we have the stars which also seem to orbit Nirn (The Star children) which are also a way to Aetherius. In the Tes universe, similar to old beliefs, Nirn is the centre of the Mundus, which is the centre of the Aurbis.

2. The spiritual world is very vague, it, I think, is Aetherius.

3.  Aurbis is the Universe.

Read this for a much better explanation:

http://www.uesp.net/wiki/Lore:Aurbis