My talk about the planes brought up a few questions by one of my faithful readers who wanted more information about how I perceive that the planes work, so, I figured, for a fun post, let's do a Q&A:
Q. Given the needed propulsion, would it be possible to, say, write my name on the sky? I'm assuming he means on the planar edge of the prime material, or, for that matter, any planar border and the answer is no.
The Domains of the gods in the Astral Plane have little to no border between them and the Astral Sea they float in, as one floats through the Astral and comes up a Domain, it begins to dominant their relative horizon until eventually you fall into that Domain and are no longer in the Astral. It's a smooth transition, there is no "pop" or cue that signifies you're in a Domain, it's much like leaving Earth's atmosphere and entering space. Scientists settled on a
"line" that separates the two, but it's not a physical separation you feel, it's just an imaginary line they all agreed upon. The same is true for the separation of Domains and the Astral, so there is no physical line to write on, anymore then you could do so on the Kármán line.
The Prime Material Plane is separated from the Astral by the Elemental Planes, these planes form a sort of shell around it, one part to have all the building blocks of Deminar readily available and one part to make it difficult for something from the Astral to wander into the Prime Material. Whatever constructed the Prime Materiel as a source of mortal life wanted to make sure it wasn't easily destroyed by beings from Beyond, and thus the Elemental Planes serve as a good barrier. And while you enter an Elemental Plane the same as you would a Domain from the Astral, you have to travel through a lot of Elemental to get to the Prime Material, and many planes are almost impossibly large, near infinite, so strolling across them from one "end" to the other is no simple journey.
The barrier between the Elemental and Prime is an actual barrier however, to stop all the Elemental stuff from constantly seeping in, but this is a Planar Barrier and is more metaphysical then physical. It exists, there is "something" there, but it's not like a hard shell or crystal sphere, it's just something stopping you from entering the Elemental Planes and stop them from entering the Prime Material.
There are holes in this Barrier, one into each of the six Elementals that allowed all that building material into the Prime to build Deminar in the first place. Some of these breaches are visible, the one into the Elemental Plane of Fire is the "Sun" which all of Deminar sees, the two "moons" are simply light reflected off the Elemental Planes of Earth and Water. There are breaches into Air, Positive, and Negative too, but those are not visible from Deminar's surfaces (thought there are claim that islands floating around the north pole of Deminar can see a radiant light show brilliance at night sometimes, possible a window in the the Elemental Plane of Positive Energy. These breaches are like that which separates the Astral from Domains, in that someone from Deminar could, in theory, fly into them and enter an Elemental Plane. However, much like earth's magnetic field, the Planar Barrier that separates the Prime from the Elementals gives off an energy that, even at its breaches still holds back stuff from tumbling into the Prime, though I wouldn't recommend getting close to the breach of the Elemental Plane of Fire without some sunscreen, cause the heat given off from it can still be felt (and indeed is felt all the way to the surfaces of Deminar)
The separation between the Prime and Ethereal is gossamer thin, which is why ghosts and such can still be seen if you know how to look, but, you can't simply pass through it, as the two planes exist in the exact same spot. Though, given the right circumstances, the veil could be thin enough that people from the Prime Material could suddenly find themselves in the Ethereal, it would make for a good adventure start at the very least.
As for what separates the Astral and the "Nothing" or Shadow Plane, well, no one, divine or otherwise, as been to the "edge" of the Astral Sea, so no one knows.
Q. Could I make an awesome shot and launch something into another plane through the sun, or a moon? See the above discussion about the "length" of the Elemental Planes, something could eventually reach the edge and wind up in the Astral Plane, but that would have to be a helluva throw, and you have to hope nothing blocks it along the way (or it's not vaporized, crushed, dissipated, or any of the other dangerous things that can happen in those planes)
Q. Do jerk beings on other planes throw their trash into Deminar?Well the Domains don't have trash, things on those planes (planar creatures included) are made from "soulstuff" and revert back to soulstuff upon being destroyed or "killed." This then gets recycled back into the Domain to be used again as needed. Though if the thing is destroyed in another Domain, say some Angels "killed" while attacking our version of Hell, the place they fall gets the "soulstuff" instead of the original owner, which is why gods are hesitant to send armies invading other Domains, it's just a good way to make a different Domain stronger. If they did have some other form of "trash" that was not soulstuff convertible, they'd have to get it through all the barriers talked about above to get to the Prime Material. One can circumvent that by opening up Planar Gates and Portals, but it's not worth the energy or effort to do so, so you probably won't find a lot of divine trash in Deminar.