Gravity plane

A gravity plane was a geometrical plane generated by certain large, non-spherical objects towards which other objects "fell". Gravity was what held an atmosphere around planets and spelljammers and what allowed an inhabitant to walk on the surface of a world or a spacefarer to stand on the deck of a ship.

Most residents of wildspace recognized that every physical object had its own gravity and assumed that the direction of the force was always towards what was most convenient for sentient life. For planets, this was always toward the center of mass, but for spelljammers and other space objects, such as asteroid cities, the force was usually perpendicular to a horizontal plane. More knowledgeable scholars of wildspace recognized that gravity planes were not natural occurrences, as was the gravity of planets, but rather the result of the special magic of spelljamming helms.

A gravity plane extended along the two horizontal axes of the massive body producing it. The plane did not terminate with the object but extended out past it such that objects fell toward the empty space surrounding the body. The object would pass through the plane and be slowed down by the suddenly opposing force in the opposite direction until it reversed direction and crossed the plane again. This would continued until it would eventually come to an equilibrium at the plane. An object resting in an empty region of the gravity plane like this would bob up and down, much like something floating on the ocean, and slowly drift away from the source of the gravity until the outer reaches of the plane, which typically extended outwards from the inducing massive object by a distance equal to that object's width. (See the figure above.)

Gravity planes had two sides; that is, they attracted objects from both the bottom and the top. It was thus possible for someone to walk on the bottom of a spelljamming vessel "upside-down".

Some vessels took advantage of these two sides in their craft designs, but most sentient creatures preferred to have only a single "up" and did not build inhabitable decks on the "bottom" side.

One of the main reasons for this "single-side" preference, was the fact that the force from a larger object's gravity plane would overcome and negate a smaller object's plane. Entering a planet's gravity well, for example, would cancel the effects of a spelljammer's gravity plane so that only the planet's gravity could be felt. Anyone walking on the bottom of a spelljammer when nearing a planet would thus plummet to the ground.