Editing Spelljammer (section)

===Crystal spheres===
{{redirect|Crystal sphere|the fortune-telling object|Crystal ball|Dungeons & Dragons adventure module|Crystal Spheres|the short story by David Brin|The Crystal Spheres}}
A crystal sphere (also known as a crystal shell) is a gigantic spherical shell which contains an entire [[planetary system]]. Each sphere varies in size but typically they are twice the diameter of the orbit of the planet that is farthest from the sun or planet at the center of the sphere (the system's primary).

The surface of the sphere is called the "sphere wall" and separates the void of "wildspace" (within the sphere) from the "phlogiston" (that surrounds and flows outside the sphere). The sphere wall has no gravity and appears to be impossible to damage by any normal or magical means. Openings in the sphere wall called "portals" allow spelljamming ships or wildspace creatures to pass through and enter or exit from a crystal sphere. Portals can spontaneously open and close anywhere on the sphere wall. Magical spells (or magical items that reproduce their effects) can allow a portal to be located. Other magic can open a new portal or collapse an existing one. Ships or creatures passing through a portal when it closes may be cut in two.

Unlike the [[Ptolemaic system]], the crystal spheres are not nested within each other.