For my home campaign, I want a universe with Black Holes (and White Holes), Nebulae, Quasars, Pulsars and Stellar Nurseries. Also, I like the concept of navigation by stars, and that Suns are stars. So this is the cosmology for me.
ASTRAL PLANE (Hyperspace, Firmament)
The Astral Plane is a great, endless "sea" of clear silvery sky, both above and below. Occasional bits of solid matter can be found here, but most of the Astral Plane is an endless, open domain. Both planar travelers and refugees from other planes call the Astral Plane home.
The Astral Plane has subjective directional gravity. It is also timeless. Age, hunger, thirst, poison, and natural healing do not function in the Astral Plane, though they resume when the traveler leaves the Astral Plane. Travel on the Astral Plane for Voidships is relatively easy once an Astral Gate is used. Ships find this route between stars quite useful. Unfortunately the Astral Plane is haunted by a number of aggressive and dangerous species, not least of which are the Astral Pirates.
CELESTIAL BODIES (Asteroids, Planets, Stars, Etc)
Celestial Bodies can have any gravity, elemental and energy traits, or magic rules, depending on the concept of the world in question. Alignment of Celestial Bodies are usually some variation on Mildly Neutral (Lawful Neutral, True Neutral, Chaotic Neutral), but some few are more strongly aligned. Celestial bodies can have any shape, though the most common is spherical. Still, there are flat worlds, elliptical worlds, cubic worlds, amorphous worlds, ring-shaped worlds, hollow worlds. Some astronomers from have even theorized the existence of a mobius world.
Large orbiting clusters of Celestial Bodies are called Solar Systems (sometime Crystal Spheres), and function almost like mini universes. A primary, core celestial body is always at the center of a Solar System, around which the other bodies "dance". Solar Systems vary greatly in size with some being only large enough for a primary Sun and a cluster of asteroids to massive systems full of immense worlds. See Planetary Zones for a more indepth description of a Solar System.
ETHERIC PLANE (Aether, The Rainbow Ocean, The Phantom Zone)
The Ethereal Plane overlaps with the Material Plane. The Material Plane is visible from the Ethereal Plane, but appears muted and indistinct, its colors blurring into each other and its edges fuzzy. While it is possible to see into the Material Plane from the Ethereal Plane, the Ethereal Plane is usually invisible to those on the Material Plane. Normally, creatures on the Ethereal Plane cannot attack creatures on the Material Plane, and vice versa. A traveler on the Ethereal Plane is invisible, incorporeal, and silent to someone on the Material Plane. The Ethereal Plane is mostly empty of structures and impediments. However, the plane has its own inhabitants. Some of these are other ethereal travelers, but the ghosts found here pose a particular peril to those who walk the fog. The plane has no gravity.
Spells function normally on the Ethereal Plane, though they do not cross into the Material Plane. The only exceptions are spells of force (magic missile, wall of force, etc.) and abjuration spells that affect ethereal
beings. Spellcasters on the Material Plane must have some way to detect foes on the Ethereal Plane before targeting them with force spells, of course. While it’s possible to hit ethereal enemies with a force spell cast
on the Material Plane, the reverse isn’t possible. No magical attacks cross from the Ethereal Plane to the Material Plane, including force attacks.
WILDSPACE (Starry Sea, Space)
Wildspace is the "space" between celestial bodies (planets, suns, etc) and between solar systems. It is considered coterminous with the Material Plane, the Astral Plane and the Etheric Plane. Wildspace is also coexistent with the Ethereal Plane, The Astral Plane, and the Plane of Shadow. Wildspace doesn't have an atmosphere of any kind and is a perfect vacuum. Conventional interplanetary journeys around a solar system take place within wildspace. It is the first obstacle that must be conquered by would-be space travelers.
Wildspace has no gravity, and is infinite, stretching out between the stars themselves (see The Void below). It is neutral in alignment, and has no elemental or energy traits. While, for the most part, magic works normally in wildspace there are some limits. Magical fire doesn't need air to work properly but if the end result a spellcaster wants requires an atmosphere (i.e. oxygen) then that end result cannot occur. For example, a Fireball spell will work but it hasn’t any chance of lighting an object or person on fire.
THE VOID: The Void is the region of wildspace beyond the edges of a solar system, and so it is a dark and deadly place. It is an airless, lifeless void so huge that distance here is measured in centuries. The Void has no gravity and has strong negative energy traits and cold dominant traits.
Spells are maximized and extended in The Void. Undead in The Void are always powerful, having maximum hit points and regenerate special abilities, with only positive energy attacks dealing permanent damage.
NAVIGATING THE SPACELANES
Travelling between planets functions as describes in Helms, however traversing the distances between Stars is another matter. The distances between stars (ie Suns) is so vast that it is measures in years rather than miles, and so even with a really fast helm, it would take centuries to manage. So some magic is needed.
The Astral Plane and The Etheric Plane are both used to travel these distances, but the Astral is the most common to Voidships. This is because the Astral is timeless, and passengers need not eat, drink or sleep. Ships with a proper course set can make it to even the farthest reaches in days, though there are dangers.
GETTING ONTO THE ASTRAL OR ETHERIC
Getting onto one of these planes can be managed via several ways. Naturally occurring gates (called Wormholes) can be found by canny navigators and pilots. Such natural gates are highly prized when discovered and those along established routes will often have asteroid bases nearby. Use of the Create Portal spell (see below) is another common means by which to use these planes. Many space creatures have a natural form of this ability.
Some enterprising species have created artificial gates for use by Voidjammers. The Fraal in particular have an affinity for creating Astral gates, even being able to do so closer to habitable worlds and subsequently easier to get to.
SETTING THE COURSE
Setting a course through The Astral Plane can be accomplished via a successful Decipher Codes check*. Success indicates that the course has been successfully set through the Silver Void. Failure results in the ship running off course to a destination of the DMs choosing.
Ships using the Astral Plane to travel to distant star systems (Spheres) take 7d10 ship days to reach their destination, regardless of travel distance. During this time the crew need not eat, drink or sleep, though many still do to repel the sheer alien-ness of the Starry Void.
*Certain spells might grant bonuses on this roll. Such as Divination, Commune, Find the Path, Scrying, Vision and similar.
Level: Cleric 5, Sor/Wiz 5
Range: Long (400 ft. + 40 ft. /level)
This spell can be cast only in the outer regions of a solar system (at the Oort Cloud). The spell causes a large area of space to become a temporarily gate onto the Astral or Etheric Plane, allowing a ship (or anything else) of suitable size to pass through. The effect lasts up to 2 hours, during which time any other ships or items may pass through, DM rolls 10d12 to determine how many minutes the portal remains open.
It takes but a fraction of a round for a ship to pass through a portal opened in this fashion. However, if the portal is dispelled or otherwise prematurely closed, roll 1d10 to determine the fate of the object passing through the opening as it closes (see table).
1–5 Portal closes before ship reaches the portal.
6 Portal closes on the ship. Ship is cut in half.
7–10 Portal closes after ship passes through.
Portals created by this spell are magical and temporary, and can be dispelled. Portals that appear naturally cannot be dispelled.
This campaign setting uses the Blood and Treasure RPG rules. Its a melding of Old School gaming and the newer, smoother-running games rules. Its a game that is fairly rules light, but has just enough crunch to satisfy my gaming appetite. All the cool kids are doing it.