The planes of the multiverse are like bubbles of reality floating in an endless sea of stars. Each material plane is a discrete, physical universe consisting of a celestial sphere (such as Earth) and a number of heavenly bodies revolving around it in empty space, all surrounded by the infinitely far-off firmament. There are dozens of known material planes that are magically connected to the Starsea, or the astral plane, which is an endless void also enclosed by the same firmament. Inter-dimensional travel is made possible by “astral channels,” naturally occurring points in the planar fabric that can be manipulated to create a bridge between the astral plane and a material plane. Certain arcane rituals can open long-lasting portals, or astral gates, along these channels. Powerful spells can create a temporary portal along the nearest astral channel, with not-always-predictable results.
The cosmography of the Starsea loosely corresponds to the geography of “nearby” material planes; that is, astral channels close to one another in a material plane are usually clustered close together in the void. The void is also dotted with enormous, floating chunks of rock, known as “freeholds,” which are often settled by inhabitants of the physical planes. Material beings must construct elaborate magical vessels to travel or live within the astral plane, which is rich in magic but inhospitable to ordinary life. Without a constant supply of magical energy, the air would slowly freeze and the flow of time would grind to a halt. Individual living beings would fall into the Deep Sleep, as frozen in time as an insect in amber, while their starships drift through the Starsea for a timeless eternity.