Forget everything you think you know about space.  In the fantasy realms of magic, the rules are quite different.  You have solar systems where the star orbits the inhabited planet, some worlds are carried around in circles by giant mystical beasts, and others just don’t move at all.  There is no limit to what can be in the Wildspace of Spelljammer.

There are some things that are consistent though.  Each system is enclosed in a gigantic crystal sphere.  These crystal spheres are completely opaque and create no gravity.  Some have small stars burning along their inside edges, others may have glowing creatures crawling along the surface creating the lights in the night sky.  All are completely unbreakable and immune to all magic and physical force. 

The impervious nature of the crystal spheres does not typically stop travel though.  Most crystal spheres have naturally occurring portals that allow ships, beings and other objects to pass through.  While a few of these portals are stationary, most move in some way.  Some drift along their crystal sphere, others teleport to a totally new location, or come and go at random times and locations.  Portals appear as a shimmering disk on the surface of the crystal sphere.  While most allow travel in both directions, there are some that are one way only and show no signs of their presence on the other side.  Stable, static portals become well know and can become very busy areas.  These areas can become economic centers, or highly pirated Wildspace highways.

The random nature of most portals can cause great difficulty in travel between crystal spheres.  There has been much magical research into these portals.  Magic spells have been devised to divine the location of portals from either side of the crystal sphere.  There are even rumors of powerful magic that can instantly create portals in the crystal spheres.  There are also stories of naturally occurring creatures than can create portals and pass through the crystal spheres.

Which leads us to the obvious question. What is outside the crystal spheres?  The phlogiston, or the phlo (pronounces “flow”) as it has come to be called.  The phlogiston is a rainbow river like substance that fills the area between crystal spheres.  It flows around them and creates natural pathways from one sphere to the another.  The crystal spheres bob like enormous corks in the rainbow rivers of the phlogiston.  Some of these rivers have been found to be quite stable and easily traveled leading to safer travel and trade between certain crystal spheres.  Others are wild and dangerous or ever changing leading to dangerous journeys between realms inside the crystal spheres. 

There is one more aspect of the phlogiston that is quite important.  It is incredibly explosive.  Any open flame will cause a rather large explosion at its source.  Any crew with any knowledge of inter-sphere travel will know to extinguish all flames before entering a portal.  All efforts to capture the flow to bring inside a crystal sphere to study or use for its combustible properties have proven ineffective, as the flow simple vanishes upon arrival inside a crystal sphere.

Inside of these crystal spheres is what is known as Wildspace.  Wildspace is all that nothing inside of the crystal spheres.  Most crystal spheres are gargantuan; their radius being double the distance from the center to the outer most orbiting body or more.  This means there is a lot of Wildspace.  Luckily, Spelljamming ships can travel at amazing speeds when outside of gravitational forces.

Which lead us to gravity.  Gravity is simple a force created by an object of mass.  All objects create gravity, their size and shape determine how that gravity affects those around it.  A spherical planet body’s gravity pulls to its center because of its shape.  The same for asteroids, moons, and the like.  Creatures, like all other objects, create their own gravity although it’s force is affected by its size with a larger gravity pull overpowering a smaller one.  It is for this reason that a Halfling adrift with a hill giant would be able to walk along the hill giant assuming the hill giant didn’t violently object.

A Spelljammer ship creates a gravity plane along it’s deck.  This gravity fields extends out a certain distance depending on the size and shape of the ship.  The double sided gravitational field can lead to much distress and complications to those who are unaccustomed to Wildspace travel.  It also causes an interesting “bobbing” effect to anything, or anyone, that is dropped overboard.  Once reaching an equilibrium along the gravitational plane, object will begin to slowly float away from the ship, eventually flying off into Wildspace once it reaches the edge of the gravitational pull of the ship.  This keeps Spelljamming ships from accumulating a debris ring, and can lead to a very dangerous situation if one should fall overboard with no way to return to the ship.

All objects that create gravity take with them an air field.  This small pocket of air is enough to provide breathable air for a man sized creature for up to 20 minutes.  Large objects bring larger air pockets.  Most ships have an air pocket that can sustain its crew and passengers for four months, even longer with less creatures using the precious air.  Once the air becomes stale, creatures will find it difficult to breathe, leading to exhaustion, disorientation, and eventually death.  Air envelopes can be refreshed off of other objects atmospheres, or through magical means. 

Spelljammer ships move through Wildspace using magic powered through a helm.  There are many different types of helms, but minor and major Spelljammer helms are by far the most common among the civilized races.  These helms take magic channeled through a magic user to move the ship.  There are helms that use other, and sometimes more nefarious, forces to power their ships. 

Throughout populated area of Wildspace, many ports exist to accommodate Spelljammers.  These ports are necessary to provide fresh area, areas to trade goods, as well as rest and relaxation for Spelljammer crews.  Ports come in all aspects from asteroids with seedy pirate towns, to moons with highly organized and protected cities built on inter-sphere trade.  There is as many different types of structures and civilizations spread throughout Wildspace as sentient being can conceive and create.

So join the crew of a Tradesman today.  See the wonders of Wildspace and the people and creatures that inhabit it.  There are adventures for everyone.  The riches of Wildspace and other realms await you, just watch out for the Neogi slavers and the Beholder war ships.  But those horrors are mostly exaggerated for effect.  The Illithid, now those are real, but are very willing to enter into mutually beneficial trade, assuming they are not very hungry.