Part of what makes Tiezerakan different is the cosmology. It is somewhat based on the ideas of Philolaus and Pythagoras rather than the Ptolemaic universe seen in D&D over the years. The differences take a bit of getting used to and at this stage, I may not have all the details figured out yet. Having said that, take what you like and adapt the rest.
For many years, it was believed that Tol, the home planet, was the center of the universe. Once humans built ships to explore the skies, it soon became very evident that this was not the case. The center of the universe is called the Central Fire or the Hearth depending upon whom you ask. Many clerics and church officials focus more on the Hearth as the lands of the Gods. Other, less religiously inclined folk, focus more on the Central Fire as a gateway to the Elemental Plane of Fire. Travel to the Central Fire has been limited as will be detailed later.
Beyond the stars is a sphere of fire called the Outer Fire. The Outer Fire is fed from the Central Fire, those the mechanism for this is not clear. Beyond the Outer Fire, it is believed that there are other spheres with planets, stars, and other central fires.
Between the Outer Fire and the Central Fire, exists the planets, the moon and the stars of the night sky. Except the sun and stars, the planets and the moon have a twin that revolves around the Central Fire exactly half a revolution away. Tol, the home planet is closest to the Central Fire. Unlike other planets, the underside of Tol has a long narrow passageway that connects to its twin planet, presumably going through the Central Fire, itself. The passageway has been called The Needle. It serves as the most reliable trade route to Tol's twin planet. Travel through the Needle requires no special protections from fire or need for extra air.
The twin planet, Lot has been explored extensively. In many ways, Lot is almost identical to Tol except that the denizens of Lot never considered extraplanetary travel.
Outside Tol, the home planet, Bulan the Moon orbits around the central fire. The moon is inhabited by a race of intelligent giants. The twin of the Moon, Ay is similar to Bulan in every way. The giants that inhabit Bulan and Ay believe that they are descendant from the Titans.
Outside Bulan/Ay lies the Sun named Caiya. Caiya is about 20 times larger than Tol and is entirely composed of a glass/quartz material. It reflects the light and heat of the Central Fire. Nothing lives on the surface of Caiya, though some believe that the interior may be inhabited.
Outside Caiya, the Sun, lies Raksa/Civah. Raksa is a tropical planet full of dense jungles. It is primarily the home to elves. Civah, it's twin, is a colder planet marked by snow for almost half the year followed by very warm summers. Mostly dwarves, gnomes and halflings make residence there. Both planets are very rich in resources and are frequent destinations for traders.
The other planets that make up the system are:
Saokin/Zohr - Zohr is an arid planet known for its magic. Saokin is considered a resort planet. It also houses the main financial center of the sphere with several trading companies headquartered here.
Peran/Muhari - Muhari is a vast swamp. Peran is the name given to a cluster of asteroids. Both planets are pirate strongholds.
Besa/Boyuk - Little is known about these planets now. Besa serves as the battleground for wars of all kinds. Boyuk is uninhabitable.
Sinsin/Uzu - Icy planet twins believed to have access to the elemental plane of water.
That's just the barest thumbnail sketch of the sphere. As always more later.