Similar to Planescape, the Spelljammer meta-setting is used to connect Morus and various other campaign settings, as well as to provide background for players wishing to explore the reaches of space. Like Planescape, some small modifications have been made to the lore and mechanics of the Spelljammer campaign setting, but for the most part it should be recognisable.
Although this is primarily a lore page, a complete rules reference can be found here.
Cosmology of the Material Plane
It is common to think of the Material Plane as a series of isolated worlds, much like the other planes of the multiverse - and that traversing from one to another is possible only with powerful magic. In practice, however, it is quite possible to physically travel from one world to another - though difficult. The medium that makes this possible is known as the Phlogiston, which resides within the Flow. Although the Flow refers to the plane itself while the Phlogiston is the medium that fills it, the two terms are often used interchangably.
The Flow is a Transitive Plane, much like the Ethereal and Astral Planes. The Phlogiston that it is made up of is what some scholars would refer to as "semi-elemental" in nature - this is to say that unlike the Elemental Planes, which are (mostly) homogenous expanses of a single element, the Phlogiston is a chaotic mixture of all of the fundamental building blocks of creation. This rich substrate forms the vast majority of the Material Plane - a great sea of potentiality just waiting for the right catalyst to impose order upon it.
The Phlogiston itself is physically invisible, but can nonetheless can be easily detected by the light it sheds - a constant, ever-changing rainbow kaleidoscope of every imaginable color. There are a few other ways it can be interacted with, as well. It burns - in fact, it is extremely flammable. Exposing any kind of open flame to the Phlogiston is suicide - the result is a massive explosion, which will continue for as long as there is fuel to burn. Once any flammable materials have been completely combusted, the fire will wink out as suddenly as it started.
The other way in which the Phlogiston can be detected is that it flows - indeed, this is where the plane gets its name. Given the vastness of the Phlogiston, this is a great boon. Although a spelljammer moves very fast when travelling at maximum speed - up to 100 million miles per day - this is nothing compared to the distances that must be covered to travel between the crystal spheres. By following the "flow rivers" that form a complex three-dimensional grid within the Phlogiston, it is possible for navigators to travel from one sphere to another in days or months rather than years.
Although flow rivers cannot be seen with the naked eye, they can be felt. An experienced helmsman will be able to feel when he has entered a river, as well as its direction of travel. This is not of much comfort, however, when "becalmed" in the vastness of the Phlogiston, with no sign of a river in sight. Many spacefaring civilisations have charts, similar to sea charts, that map out known rivers and the spheres to which they travel - a wise explorer obtains such a chart rather than venturing into the universe without preparation.
Finally, while the Phlogiston may seem like a seething ocean of unformed chaos-stuff, it is not entirely uniform. There are "sargassos", dead magic zones with very little Phlogiston. These zones will immediately cause a Spelljammer to stop functioning if it enters, and are in some cases littered with dead vessels that have met this fate. There are also strange and often dangerous creatures that dwell in the Phlogiston itself, and some foolhardy types even try to establish colonies in the Flow.
The Crystal Spheres
As noted above, the Phlogiston is composed of amorphous elemental material, fluid in form. There are places, however, where this chaotic medium has been collapsed, separated and ordered into recognisable matter by some force or another - into rock and iron, air and water. Theories abound as to what it is that causes this to happen - ranging from natural phenomena to divine intervention - but none can say for sure how order is brought to this primal chaos. It is known, however, that the gods cannot influence the Phlogiston directly. Their influence on the Material only extends into crystal spheres where they have worshipers.
A crystal sphere is a massive "shell" of an unbreakable, unidentifiable material - large enough to enclose an entire solar system, though they vary in size. When viewed up close, it appears to be a dark, glass-like material that feels like ceramic when touched. Although the material is completely transparent, the shifting colors of the Phlogiston cannot be seen through a crystal sphere - it effectively renders them invisible. This means that distant features such as stars can be seen from the surface of a world even though they may reside in crystal spheres many millions of miles away. Although the spheres are unbreakable by most physical and magical means, there are various ways to pass through them and into the Flow - these are documented at the bottom of this page, in the section on spelljamming.
Within a crystal sphere, the Phlogiston gives way to the vacuum of wildspace - a black, airless void. It is very similar to what most people would think of as "space", although the laws of physics (especially gravitation) operate very differently than they do in the real world. It is within the reaches of Wildspace that one finds stars, planets, asteroids, moons and all other manner of celestial body. However, each sphere is self-contained and has its own natural laws. In one sphere, planets may orbit the sun; in another, stars may orbit planets; in a third, planets are placed upon the back of a great turtle - and so on.
It is impossible to bring the Phlogiston into a crystal sphere in its natural and chaotic form. Any attempt to do so results in it dissipating with a bright flash and a hissing sound, presumably separating into various gases and dusts of ordered matter.
It is a common misconception amongst those who dwell on the surface of a planet that the glittering lights that twinkle in the sky are all members of a single numerous class. This is far from the truth - a star is simply any large, luminous object within a crystal sphere that is bright enough to be seen from other crystal spheres.
The majority of stars are similar to stars in the real world - massive sources of light and heat that serve to provide energy to the worlds in their system. Instead of great fusion reactors, however, these suns are usually massive portals to the Plane of Fire or the Plane of Radiance. It is unclear who is responsible for the presence of suns in so many habitable systems; it is possible that they form naturally under the right conditions when a crystal sphere is created. After all, if the Phlogiston is formed of all four elements, there should logically be Elemental Fire in there somewhere. As they are so essential to life, it is also possible that the unknown architects of the crystal spheres are also responsible for furnishing them with a star.
Other stars that can be seen in the night sky have different origins. Some are not so far away as they may seem - they might be a distant planet, an outpost in wildspace or a great interstellar portal created by some deity to watch the world through. Still others are natural portals on the inner surface of a crystal sphere, by which one may egress into the Phlogiston. Some may indeed be distant suns in other systems, while others may be other sources of bright light that are shining from far away.
The crystal sphere that surrounds the world of Morus is about 6500 years old, and has been fairly stable since it was first created. The system it contains is very much like our own, without pyramid-shaped suns or spacefaring turtles. It contains a sun, around which revolve planets with or without moons. The planet furthest from the sun is Rimtar, and thus the size of the crystal sphere is only slightly larger than the orbit of Mars in our own solar system (a radius of about 160 million miles).
At present, only two known flow rivers connect Moruspace to other spheres, both one way. A one-way river flows from Greyspace to Moruspace (this is the one that Melf uses), and another flows from Moruspace to Winterspace. Note that this section may be expanded as new features of Moruspace are discovered.
The largest and principal world of Moruspace, it is the most developed civilisation within the sphere. Despite this, however, it has almost no spacefaring capability. Outside of some very experimental forms of magic being developed in Kyujitai and a few ancient wreckages of fallen spelljammers from prehistory, there is no space travel to speak of from Morus.
Morus is a large, earth-like planet about double the size of our own world. It is bisected along the equator by the Boiling Ocean, a magical body of water that is impassable by sea. The "known world" of Morus is entirely based within the northern hemisphere, with the southern hemisphere being firmly in the territory of "mare incognita". Indeed, there is intense debate about whether there is anything south of the Boiling Ocean at all.
Morus is orbited by two moons: Wintera and Sanguina.
From the surface of Morus, Wintera appears to be the larger of its two moons. In truth, however, it is smaller but closer - a mere 170,000 miles away. Wintera appears to be pure white in color, with no visible blemishes or features of any kind. Because Morus is not a spacefaring world, there are many theories and legends about its twin moons - and none capture the imagine so much as Wintera. The elves of Morus believe it carries the essence of Selune the Lady of Silver, waxing and waning as her attention wavers between the many worlds she safeguards.
Whether these legends are true or not, one thing is true of Wintera - it is a moon that moves constantly in and out of the Material Plane. Unlike most moons, which change in phase as they orbit the world, Wintera is always fixed in place. As it waxes and wanes, it disappears into the Ethereal Plane and returns to the Material. Since it is in constant movement between the worlds of the physical and the spirit, it is a haven for beings of ethereal nature and a powerful gateway into the spirit world.
Although few have managed to visit Wintera and return, it is said that the surface of the moon is covered constantly by heavy snows - a consequence of a river that flows through it while it is in the spirit world. When it returns the Material, the extreme cold freezes over these rivers and causes the clouds to fall to its surface as snow. There are strange shapes and structures on the surface of the moon which can be observed by powerful lenses - these are thought to be the homes of the fey beings which make their homes there.
Just as Wintera appears to be large due to its close proximity to Morus, Sanguina only appears small because of its great distance. In truth, it is much larger than Wintera, but is a remote 350,000 miles from Morus. Whereas Wintera is stark white, the surface of Sanguina is bright red as a result of high concentrations of iron in the soil. It is known as the "blood moon" on Morus, and where Wintera is an object of mystery and wonder, Sanguina is commonly looked at with reverence and even fear. It is a focus of many cults and is popular with necromancers. As Sanguina waxes and wanes especially slowly - growing to fullness only once every 3 months - the full mooon is often incorporated into rituals dealing with blood magic or spirit magic.
Perhaps because of the dire worship directed towards it, or perhaps because of the great quantities of iron to be found there, the surface of Sanguina is a very active place. Although it is very thin and difficult to breathe, Sanguina does have an atmosphere of its own - produced by deep underground fungi that feed on rust and magical energy. Frequent storms blow across the landscape, laced with tiny fragments of iron that can shred flesh like paper. Most notable, however, are the iron elementals that sporadically animate from the surface of the moon, roaming the surface and killing any they come across.
Despite its inhospitability, Sanguina is not completely uninhabited. A number of duergar have used pathways through the Plane of Elemental Earth to establish colonies beneath the surface, using it as a lucrative mine to extract large quantities of iron ore from. They frequently come into conflict with the iron elementals and the other unusual native denizens of Sanguina, whose caves are home to many types of animated fungi.
At the outer edge of Moruspace (30 million miles from Morus), dimly visible as a reddish star from Morus, is the great planet of Rimtar, which means 'Our Castle' in dwarven. A small planet about 1/8th the size of Morus, it is home to the only spacefaring civilisation within the sphere, a dwarven one called the Moredi. They are descended from the Ancestor Dwarves of Morus, who perished in ancient times in battle with what they called the "Ancient Masters". While most of the Ancestors perished, and some chose to hide themselves beneath the earth, another group banded together and called upon the power of Moradin to lift their fortress from the surface of Morus and carry it safely into wildspace. They settled upon Rimtar and have called it home ever since.
As planets go, Rimtar is a fairly desolate one. While it has an airy atmosphere of its own, its surface is rocky and devoid of any vegetation at all. Air and water to the planet is supplied by portals into the Elemental Planes operated by Moredi priests, who specialise in such transportive magics. If these were to fail, the lack of plant life or naturally occuring water would render it into an uninhabitable rock. Most sadly for the dwarves, however, Rimtar is very poor in natural resources - iron, steel, gold and all the other things that the dwarves need to make their crafts.
This is why the Moredi's journeys through wildspace did not end with their settlement on Rimtar. Travelling throughout Moruspace on massive vessels carved out of small asteroids, the Moredi spacefarers provide their colony with everything it needs to persist. They land on the asteroids that dot Moruspace and mine the valuable minerals to be found within. Their massive spacecraft are too large, however, to land on the surface of Morus. There may be other reasons the Moredi have chosen not to return to the homeworld of their ancestors, but they are not known.
As might be surmrised from their ability to travel through space, the Moredi are a highly advanced race. The wisdom and magics that were lost by the dwarves of Morus when they retreated into the Ancestor Forges were retained by the Moredi, and they are especially proficient at the creation of spelljamming devices and transportive rune-magic. Once every Rimtaran year (2 Morus years), the planet draws very close to a portal in the crystal sphere of Moruspace. During this period, which lasts about a month, the Moredi send expeditions into other spheres.
Ishtar, the final planet in the system, is closer to the sun than any other - 40 million miles from Morus, and 60 million miles from the sun. The surface of Ishtar is incredibly hot, reaching temperatures of 400 degrees, and its atmosphere is incredibly dense. Although it has no known vegetation, its thick (and poisonous) atmosphere is expelled by the massive amounts of volcanic activity present on the planet's surface. It is the brightest star in the night sky of Morus, appearing as a glimmering white light.
Ishtar is one of the more mysterious planets in Moruspace, and very little is known about what lies beyond its opaque, reflective atmosphere. It is about 3/4 of the size of Morus and has an orbital period of about 9 months.
The Broken World
About 10 million miles from Morus along the most direct route to Rimtar, there exists an asteroid field of unprecedented size. This asteroid field - one of the most profitable regions for Rimtaran mining colonies - is the broken and shattered remains of a planet that was destroyed long ago. Little is known about what this planet was like before it was destroyed, or even how long ago it happened. However, there are the remnants of stone edifices on some asteroids which imply a distinctly illithid background. As yet, however, the Rimtaran dwaves have yet to uncover anything beyond ruined stonework in their operations.
Burning in the center of the crystal sphere 100 million miles from Morus, the sun of Moruspace is typical in many ways. Like many such suns, it is a massive portal to one of the deepest regions of the Plane of Elemental Fire, releasing massive amounts of heat and light into the void around it. It is totally unknown to any of the denizens of Moruspace how it came to be, and none have attempted any kind of serious investigation.
Surviving In Space
Luckily, gravity is far more accomodating in the Material Plane than it is in our real world. It follows a principle of convenience; in planet-sized objects, it pulls towards the center of mass. In smaller objects, such as spacecraft, it is a bi-directional plane that cuts through the object horizontally. This means, for example, that you can stand on the deck of a ship. It also means that you could stand just as easily on its hull, if you desire. The only requirement is that the object's axis is at least 25 feet long.
An object that falls into the gravity plane of a vessel, then, will oscillate back and forth between the two gravity planes. A slight outward force is applied along the plane, meaning that such an object will get further and further away until it eventually escapes the ship's gravity and is expelled into wildspace.
Gravity within the Spelljammer universe is an all-or-nothing deal. If an object is large enough to exert gravity, it exerts the same amount of gravity as one would experience on the surface of Morus. The only thing that changes is how far out that gravity extends. The gravity field of an object extends to an all-around depth equal to the object's cross-sectional diameter.
It is entirely possible for the gravity fields of two large objects to intersect each other without difficulty. Crew members and so on are affected by the gravity of whichever object is closer to them, making it possible to jump from one ship to another while boarding, for example. It is only when the two objects come into physical contact that this changes - at this point, the gravity (and spelljamming helm, if any) of the larger object asserts itself and is dominant.
Another problem facing spacefarers is also (partially) solved by the unique way in which gravity works. Although wildspace is an airless void and Phlogiston is unbreathable, the gravity of an object that leaves its own atmosphere is sufficient to drag an "air envelope" along with it. For most living creatures, this envelope only contains enough air to sustain them for 2d10 turns. More massive creatures like ogres and giants bring more air with them, but also need more - they can last for twice as long. Even so, this is scarcely enough to travel anywhere. Larger objects, such as ships, are rated by tonnage. Each ton represents 100 cubic yards of space, which brings along enough air for a single human-sized creature to breathe comfortably for 4 months.
Once your air envelope "runs out", you do not immediately suffocate. Instead, the air quality degrades into "foul air". This is air that is humid, smells bad and is partially depleted. For a human-sized creature, the air is fouled from the time it runs out until the thirieth turn (larger creatures double this, as before). For a ship, the air remains foul (but breathable) for as long as its original "clean duration". So an envelope that can comfortably support you for 4 months can be breathed at a stretch for 8 months.
After the fouled air expires completely, it becomes deadly air - full of carbon dioxide. Breathing this air requires a saving throw vs. poison each turn. Failure causes you to pass out, and a second failure causes death. A creature that has passed out due to deadly air can only be revided by fresh, clean air. The only time this changes is in the Phlogiston - there, running out of air does not result in death, but a state of suspended animation where the skin becomes grey and stonelike until revival.
Combat in weightless conditions is extremely difficult for those who are unaccustomed to it. On board a ship or other gravitating object, there is no difference between terrestial combat and combat in space. While weightless, however, a lack of familiarity with zero-gravity, three-dimensional fighting causes characters to take a -6 penalty to initiative and a -2 penalty to attack rolls. Taking the Weightless Combat fighting style for one slot will mitigate this, as will being a native to space.
Within a gravity field, missile combat functions normally. Once a missile leaves the gravity field, however, the forces of gravity and air resistance cease to function. As such, it can effectively continue endlessly - this means that all missile weapons have an "extreme range" which is equal to the maximum distance that can be seen. Shots fired at extreme range are made at a -10 penalty, and they travel at a rate per round equal to their long-range distance.
Attacks with fire and other gases in space behave very unusually. Obviously, using fire in the Phlogiston is strongly inadvisable due to its inflammable nature. In wildspace, fire-based spells will work normally within the air envelope. However, it's impossible for a fire spell to cross wildspace. Once it leaves the air envelope, it will simply fizzle. Likewise, sound-based attacks with rely on air cannot be transmitted through wildspace, and neither can gaseous attacks that rely in dispersion through air.
When it comes to space travel, most mundane magics simply do not have what it takes to traverse space. A magic carpet might be a powerful magic item, but compared to the immense distance between worlds it is utterly impractical. Only a spelljamming helm can provide enough motive force to propel a vessel over millions of miles in the space of a single day.
The most basic form of helm are the minor and major spelljamming helms, which can be aquired for around 100,000 and 250,000 gp respectively, in places where Arcane merchants sell them. They allow spell energy - from either mages or priests - to be channelled directly into motive force. This energy is mostly used to propel the ship forwards, with most maneuvering coming from the sails and oars.
The minor helm confers a ship rating (SR) of 1 for every 3 levels of experience of its pilot. The major helm confers 1 SR for every 2 levels. Any spellcaster who operates a helm loses their ability to cast spells for the rest of the day. Activation time is not important; the spellcaster is drained of all spells the moment it is activated, and thereafter he is simply directing the helm in how to use the energy it has drawn from them. Spells may be cast again once the spellcaster has rested and studied or prayed, as normal.
A minor helm can move a ship of up to 50 tons, while a major helm can move up to 100 tons. There are various other types of helm - series helms used by illithids with psionic powers, forge helms used by dwarves that are powered by creative endeavours, and even furnace helms that work by consuming magic items. These can be found in the Spelljammer rulebook.
While seated on the spelljamming helm, a pilot feels as though immersed in warm water. The ship becomes an extension of their own body, and they can see around the deck as if he were standing on it. Piloting requires minimal effort, and is akin to walking in terms of how much concentration it requires - it is quite possible to converse with others while piloting, for example. Either type of spelljamming helm can be comfortably used for 12 hours without tiring; after this, the SR will drop by 1 every hour to a minimum of 1. After 24 hours, the pilot will collapse from exhaustion and will not be able to use the helm again until fully rested.
Travelling within the atmosphere of a planet is the most dangerous and slow of all for a spelljamming vessel. Ships move at a rate of 500 yards per round for every point of the ship's rating (SR) that it has. This translates to 17 MPH or 400 miles per day for each point of SR. However, if travelling at faster than 500 yards per round, any crew members on deck must make a saving throw vs. paralyzation each round or be blown off by the wind. Although this may seem like a very fast speed, it is mitigated by a few factors.
First of all, ships that are flying far above the surface of a planet have weather to contend with; spelljamming ships are ill suited to deal with storms and powerful winds. When a spelljammer is caught in a storm the vessel must make a saving throw versus crushing blow each turn. This save can be modfied in several ways. If all sails are taken down and secured (reducing the ship's maneuverability to "F") then the save is made at +4. Additionally, if the helmsman has the Spelljammer proficiency, he can add +1 to the roll. Regardless, if the roll fails the ship suffers a random critical hit.
The second impediment to atmospheric flight is the air resistance and gravity of the planet they are visiting. Taking off from a planet or planetoid (of size class A or greater) takes 1d8 rounds before enough energy is built up by the helm to overcome the force of normal gravity and take off. After take off, the time taken to escape a planet's gravity well and enter wildspace can vary from 10 minutes to 16 hours, depending on the size class of the planet. Landing safely takes about the same amount of time, and can only be done by ships that are able to touch down on land or water.
Once you have escaped the atmosphere, a spelljammer can reach incredibly high speeds in a straight line - up to 100 million miles per day, or about 4 million miles per hour. However, "straight line" is the operative word. If the ship must make a turn, or if it comes within the gravity well of any body of more than 10 tons in size, it deccelerates to its "normal" (tactical) speed. Luckily, objects that are smaller than 10 tons are not a danger at this speed - they simply get caught in the ship's gravity well, bounce around a bit, then get deposited behind it.
The only thing that complicates travel in wildspace is the aforementioned celestial bodies. If the most direct path to your route will take you through the gravity well of another planet, then your journey will be accordingly slowed. If you wish to move straight on after slowing down, you can do so, but only after the obligatory 1d8 rounds required to "warm up" and escape the planet's gravity well. This is mostly a problem when navigating areas of wildspace crowded by dense ships or asteroids, where you are constantly deccelerating and accelerating.
Getting to the Phlogiston is the difficult part of Phlogiston travel - bypassing the crystal spheres requires that you find a naturally occuring portal through the sphere or wield a suitable spell or device that will allow you to pass through it safely. Once you have done so, however, Phlogiston travel is not particularly difficult. Except in certain respects, such as the flammability of Phlogiston, travel in the Flow is the same as in wildspace.
There is, however, one significant difference. While the distance between planets in wildspace might be millions of miles, the distance between even nearby crystal spheres in the Flow might be tens of trillions of miles. Even for the fastest of craft, this would take years to traverse. The solution, of course, are the flow rivers, but travelling them requires either a great deal of luck or some foreknowledge of where to find them. Star charts are essential for any spacefarer attempting to travel the universe.
Assuming a suitable flow river can be found that will take you to another crystal sphere, travel in the Phlogiston generally takes between 10 and 100 days between spheres.