Celestial Sphere

The following is an excerpt from Dark Dungeons, Chapter 15: Out of This World:

Although incredibly huge, the void is not endless. It is bounded by a shell of crystalline material called the Celestial Sphere.

The sphere is impervious to any physical or magical damage, even from Immortals.

Assuming your campaign world is not terribly unusual, the sphere will contain either a sun in the centre with a number of planets orbiting it, or a central planet that is orbited by a sun and one or more other moons and planets.

In either case, the radius of the sphere will always be at least twice the radius at which the outermost planet orbits.

Dotted around the sphere are glowing points of light that can be seen as stars from the various planets in the sphere. These are a part of the sphere, and cannot be moved or damaged in any way. However, they are useful for navigation, and provide a dim light in the absence of a sun.

Astronomical Bodies

The astronomical bodies—planets and sun(s)—in the sphere can be loosely categorised into four types, corresponding to the four states of matter:

  • Gaseous Body: A gaseous body is a gas planet. The body of the planet is made of air or some similar gas, and it is not usually possible to tell where the air envelope stops and the planet itself starts. A gaseous body may have a small core at the centre, composed of debris that has accumulated there, but generally it is entirely composed of air. A gaseous planet usually has extremely violent weather patterns.
  • Solid Body: A solid body is a solid planet like our own Earth. It will be primarily composed of rock, and have a normal atmosphere. Dark Dungeons assumes that the campaign is set on a solid body.
  • Radiating Body: A radiating body is a sun. There is usually one per sphere, and it is often in the centre. A sun provides light for the whole sphere; without a sun the sphere is dark and lit only by the stars. However, a sun is not necessary to provide heat in the void. A sphere without a sun will be cold enough to freeze water, but will still be warm enough to survive in. If the gravity and air envelope of a radiating body is entered, treat it as if on the elemental plane of fire, with the exception that there is no ground. The planet is usually fire all the way to the centre, since any debris that would accumulate there will typically burn up.
  • Liquid Body: A liquid planet is basically a large blob of water or a similar liquid, forming a planet that is entirely sea. It may have a small core made of debris, and may also have small islands of floating debris, possibly even with settlers or refugees living on them. The atmosphere of a water planet is normal.

In a sphere without a sun, a liquid planet will be a frozen ball of ice and snow rather than liquid water.