Greyspace is the common name given to the planetary system of Oerth.
Unlike most planetary systems, Greyspace is geocentric; a terrestrial body—in this case, Oerth—is the center of the system, about which other celestial bodies orbit.
The Missionaries of Celestian
As the name suggests, the Missionaries are followers of Celestian, God of the Universe. They are somewhat different from most followers of Celestian, in that they rarely sign on to other ships. The Missionaries are a specific order of priests and paladins that travel about on modified Barges of Ptah. They actively search for damaged ships, and when they find one, they immediately do what they can to heal anyone on board who requires aid. Failing that, they try to get the injured party to a world or asteroid where better medical facilities are available. If even this is impossible (the person dies), they make certain to grant the individual a burial in space, with full honor. To view a Missionary barge as a "hospital ship" would be fairly accurate.
This group is at odds with the followers of Ptah, as is to be expected, but they do not fight. In fact, the Missionaries only fight other ships when they must. The barges they use often have magical devices or spells to increase maneuverability or armor rating.
Most spacefaring groups let the Missionaries go where they will, and NEVER attack them (even pirates let them pass). The reason is simple: you never know when you may need their help. Those groups that have offended the Missionaries in the past (the Tenth Pit for example) have never received their aid, no matter how desperately they need it.
Sadly, many pirates have tried to take advantage of this "hands off" attitude that most have toward the Missionaries, and have tried to pass themselves off as members. This has forced many leaders to search the Barges before allowing them docking or landing rights. The most notable examples of this are the Kingdom of Ratik on Oerth, the city of Waterdeep on Toril, and the Rock of Bral. The Missionaries understand this, and allow it to continue. So far, the number of pirate impostors has been quite low.
The Missionaries of Celestian are based on Oerth.
The crystal sphere
Greyspace, like all planetary systems in the Spelljammer universe, is encased in a vast sphere of an indestructible substance. At 16 billion miles across, Greyspace's sphere is one of the largest known. From the outside it is as reflective as polished steel, and from a distance beautiful colors, like the iridescent hues in mother-of-pearl, can be discerned. From the inside it is night-black and completely nonreflective. It is, in fact, the night sky itself. It cannot be touched, exactly; it is perceivable only as a barrier beyond which nothing can go, except through portals opened magically into the chaos outside.
The "stars" that can be seen on clear nights are actually titanic gemstones somehow buried in the surface of the sphere. It has been surmised that they contain portals within them to the Positive Energy Plane or the Quasielemental Plane of Radiance, or that they were mined from the gods from the stuff of the Positive Energy Plane. The heat from them can only be felt from less than a hundred feet away (where it is deadly), but their light can be seen (obviously) for billions of miles. The constellations are described as occupying the midpoint between Law and Chaos; patterns can be discerned, but the greater order behind them, if any, seems elusive. Oerthly sages identify 12 Lairs of the Zodiac and have given names to many other constellations as well, such as the Druid, the Dancer of Swords, and the Swan.
Terrestrial planet and home to the city of Greyhawk
Tidally-locked terrestrial body. Covered with the ruins of a humanoid civilization, but lacking any air whatsoever. A magical cataclysm is suspected to have caused the depopulation. Also known as Celene, one of Oerth's "moons."
Terrestrial planet, covered with earthlike features, including animals and monsters, but no sentient life. Also known as Luna, one of Oerth's "moons."
Liga, the sun
Star. Has many small lakes of elemental water to keep it from burning too hot. Larger than Oerth, but orbits it anyway.
Spherical asteroid belt.
Gas giant, populated primarily by dragons.
Dark-red gas giant, with blobs of lava and shards of ice in the interior. Contains a gate to the Negative Material Plane. Populated primarily by undead.
Elliptical water world with two solid cores that orbit around each other. Populated by many piscine creatures, including merfolk and sahuagin.
Crescent-shaped world that resembles a sphere with a giant bite taken out of it. Has an atmosphere on the inside of the crescent. Basic civilized fantasy world.
Spherical asteroid cluster with a common atmosphere. Formerly a planet inhabited by orcs, goblins and other humanoids, it was devastated by the magic of the elves.
Another spherical asteroid cluster with a common atmosphere, although many of the asteroids bear huge forests. Home to elves.
A flat, circular disc of rock that appears to vanish and re-appear as it is seen edgewise, then rotates to show its full face. Also called The Wink. Has an atmosphere and water, but no life.
At least three objects similar to Spheres of Annihilation, but several miles in diameter.
The Great Sargasso
A region of dead magic a million miles in diameter.
- A mile-long ellipsoid of some dark blue-gray metal (perhaps
superficially resembling the far smaller artifact in the Pits of Azak-Zil).
- A constellation of nine star-like objects, resembling a single
bright star from Oerth. They are surrounded by a region of reverse gravity and dead magic. Those who pass between them end up far removed in space or time.
Cannonfire Homepage- http://www.canonfire.com/cf/index.php
Greywiki Greyspace Article- http://www.canonfire.com/wiki/index.php?title=Greyspace
Spelljammer .ORG Greyspace Article- http://www.spelljammer.org/worlds/Greyspace/
Spelljammer Wiki Greyspace Article- http://spelljammer.wikia.com/wiki/Greyspace