Aethra ☰
Aethra is not the only planet in its solar system. It has one moon, Suki, which is similar in nearly every way to Earth's own Luna Selene; however, Suki itself has its own, much smaller satellite - Suki Minor - that orbits it and affects Aethra's tides in minor ways. Will expand later.
The planes of Aethra's universe, while they do exist physically, do not exist in the same dimension as the Central Plane, instead each occupying their own layer of reality, overlapping and coexisting with each other separate, but together. Inherently different, yet intrisically linked in a way that is impossible to comprehend for mortal minds that do not exist in such a cosmic paradigm.
At the center of all of the Elemental Planes, taking a piece from all of them and becoming greater for it, is the aptly-named Central Plane. The planes themselves can be read about in further and greater detail here.