To make things simpler on myself, and because I don’t want to study astronomy, I decided to make my other world quite earth-like. There is but one moon, about the same size as our moon, and only one sun, about the same size as our sun, and they are both about as far from the planet as their real world equivalents. There are ten planets in the solar system and they are a bit different, with their own names and number of moons, but they’re only likely to come up as mentions during alchemical talks (and even then, only maybe) so I didn’t go into much more detail with them rather than risk getting the solar system wrong. The stars are suns burning billions of kilometers away, though different races think otherwise.
The primary difference is that this is animistic world. There is a spirit in everything of varying ages and strengths. Some of these spirits can materialize from their physical anchor. Some can free themselves of it and clothe themselves in flesh (the sidhe) and even forget that they were anything but creatures of meat and matter. Some mostly exist in the in-between-places that are not in the world of matter, yet not devoid of it, like pocket realms that exist where nothing else should. These can be an oasis behind a desert tree, a Narnia in a closet, or a hiding place in a shadow.
In space, the spirits are ancient and unchanging beings, hostile to life, that slither between the black spaces and coil in the hearts of ancient suns. They sometimes crash to this world on the meteors or are summoned to this planet and whenever this happens, devastation soon follows. These are monstrous and unknowable though some confuse them for a God that may never have even existed. These beings do not comprehend life as we understand it. Some would toy with us. Some destroy us or craft us anew. Some simply wouldn’t notice us but their presence would be as bad. Some say that the dragons were spawned from these places and that they took flight to our planet so long ago – either from a place of monsters or another living planet that suffered some long-lost calamity. They came to our world, slipping through the in-between-places and laying claim to territories that they could control on an almost base level. But then, few claim to have seen a dragon, so perhaps they are but a myth.