Spheres are the ever-present bodies of earth that float high above the Infinite Ocean. They are inhabited by a number of races, and each is unique in its own way.
Spheres are often located at least 100 km from the surface of the Infinite Ocean's waves, rooted in place and incapable of being moved from their place. A central sphere is unanimously agreed to be the "center" of the world of Aurora, as the density of Spheres in the sky decreases evenly in all directions as one moves away from this Sphere.
In this central location, Sphere density is so high that neighboring Spheres are at times no more than a few dozen miles away from the surface of another. Their orientation compared to each other varies, some being higher than others or lower comapred to the Infinite Ocean which is considered the "ground" so to speak.
As one moves away from the central Sphere into the horizon of the ocean, this density decreases and Spheres become increasingly distanced from another. Eventually, when one travels far enough, the Spheres become so distant that one could travel for years and fail to see another Sphere in the sky. It is believed that eventually Spheres cease to exist at a certain distance.
All Spheres exist in the same sky above the ocean, meaning that they share the same atmosphere as one another. Even as one leaves the surface of their planet, oxygen and "air" does not cease to exist or thin in any way.
The area far above the Spheres and their sky appears to be a black space, much like in our own universe. A sun exists in this area, far beyond the reach of Aurorans. However, much like the Spheres, this sun does not move from its place. Instead, it ignites (becoming bright) and extinguishes (becoming dark) daily to create the effect of day and night. As Spheres rotate in place, they get periods of "dim" and "bright" during the daytime, depending on one's position on the Sphere. When the hemisphere one is standing on for their Sphere points towards the ocean and away from the sun, it is the Dim Period (they still recieve reflected sunlight from the ocean below). When it is facing upwards, it is the Bright Period, recieving sunlight directly from the source.
When the sun extinguishes at night, darkness is the same for all Spheres. Only the light of many stars barely lights their night sky. The transition between daytime and nighttime is gradual just like ours, with the sun growing brighter or darker through the daily period.
Spheres all possess their own gravitational pull, which is universal for all Spheres no matter their size; the largest Sphere will have the same gravitational magnitude as the tiniest Sphere. What does vary between size, however, is the distance at which their gravity affects things. This distance is called the "Gravity Threshold Distance" and defines the point at which gravity is no longer created by the Sphere, and switches to that of the Infinite Ocean's. This sphere of influence is not gradual in effect, causing an abrupt shift in gravity when airships go beyond it.
The GTD is related linearly to the diameter of the Sphere by the following equation:
G = 0.107 * D
...where G is the GTD in kilometers, and D is the diameter of the Sphere in kilometers.