Much like a body in space carries its own air envelope, a gathering of celestial bodies carries between them a sphere of vacuous, empty space on the Prime Material Plane. This area is known as Wildspace, and the planets and suns within make up a Wildspace System, or Sphere. Each sphere varies in size but typically they are twice the diameter of the orbit of the planet farthest from the sun or planet at the center of the sphere (the system’s primary).

Spelljamming ships normally move very, very quickly, covering a hundred million miles per day. In comparison to these great speeds, the planets move incredibly slowly; so slowly that they can be thought of as being fixed points on the firmament. A ready comparison is the continents and islands in an ocean, rather than being fixed in place, moving very slowly in comparison with the ships that move about them.

A wildspace system usually, but not always, centers around a primary celestial body, orbited by an array of other objects and plants. The primary of a system is usually a star or other elemental fire body. Whether operating under Newtonian physics, riding on the back of giant turtles, or rolling across the velvet of the gods’ pool table, most planets array themselves in orbits around the system’s primary body. In the case of Oerth, the planet containing Greyhawk is at the center of the system and all other bodies (including the sun) revolve around it.