The Great Wheel as a Planar Orrery

This is a work in progress, but I thought I'd post what I've gotten done so far here for feedback. There's a lot in Planescape that really implies that the multiverse functions according to the orrery model - the Modron Orrery, the celestial aetherscopes, the way the doors in Doors to the Unknown work, the weird diagrams and things in the margins of the poster maps, and of course the Outlands calendar on the Mimir, which is the primary basis of this.

Ultimately, this sort of system governs the opening and closing of portals - even, perhaps, in Sigil itself. Whether a given opening is a portal to Baator, Arborea, or Neth the Demiplane That Lives depends on the relative positions of the various planes in some vast metaphysical scheme.

This could get really complicated if I let it. Many of the layers of the planes could move in complex patterns relative to one another. I'm thinking Mechanus originally had eight seasons, for example, based on the influence of the Outlands, the four layers of Acheron, and the three layers of Arcadia (until one layer disappeared - though that might make the whole Nemausus incident to obvious and hard for the Harmonium to cover up). And do the inner planes cast an influence over the Outer Planes, however slight? There could be a complex chart showing how various outer planes change depending on whether earth, air, fire, water, positive, or negative energy is dominant, even though the inner and outer planes don't touch anywhere directly (aside from a few artificial portals).

And how much do the various material spheres influence the outer and inner planes? Is it important to Arcadia that Eberron is currently waxing and Athas is waning? Probably not very. The influence over the outer, inner, transitive, and demiplanes over much of the Prime can't be overestimated, however.

Incidently, Oerth's calendar conveniently has exactly 364 days in a year, just like Sigil and the Outlands. It's harder to synchronize Toril's calendar, which has 365 1/4 days in a year.

Definitions of Terms

True conjunction means that the planar traits of another plane have begun bleeding into another plane. Portals open where none existed before, and permanent portals become usuable without keys.

Conjunction means the two planes are coterminous. Spells that cross planes can affect a plane in conjunction with another, and natural portals between the two planes may exist (though they usually require keys).

Severance means that at least one plane exists between the two planes. Spells may not affect a plane in severance with another directly. Any portals between two planes in severance will be artificially created.

The Outlands

Planes in conjunction: Abyss, Carceri, Hades, Gehenna, Baator, Acheron, Mechanus, Arcadia, Celestia, Bytopia, Elysium, Beastlands, Arborea, Ysgard, Limbo, Pandemonium, Astral Plane, Material Plane.

Each plane on the Great Ring enters into true conjunction with the Outlands for approximately 21 days. For a week each year, the Outlands enters into true conjunction with the Astral Plane.

The Outlands never enters into true conjunction with the Material Plane. The presence of the Spire is thought to prohibit it.

The Abyss

Planes in conjunction: Pandemonium, Gray Waste, Outlands, Astral, Material Plane, Shadow

The various layers of the Abyss enter in and out of conjunction with one another randomly, most circling, more or less, around the Plain of Infinite Portals. The Outlands enters into true conjunction with the Plain of Infinite Portals for approximately 21 days a year, usually at about the same time. Carceri and Pandemonium both enter into true conjunction with the Abyss for several months at a time, though this period varies. On a random week most years, the Plain of Infinite Portals enters into true conjunction with the Astral Plane. Other layers of the Abyss seldom enter into conjunction with other planes, but this occasionally happens. Complicated calculations with celestial aetherscopes make these times easier to predict.

Occasionally, one or more layers of the Abyss may enter into true conjunction with the Material Plane. The timing of this is uncertain, but acts of extreme depravity and the sacrifice of souls to demon princes may hasten it.

Carceri

Planes in conjunction: Abyss, Gray Waste, Outlands, Astral, Material Plane

For several months at a random time each year, the Abyss and Carceri enter into true conjunction in an event known as the Rotting, The weather becomes cold and the foliage of the Red Prison begins to decay. New portals do not open from Carceri's end, but on a single day each year a few portals may become passable without keys. The prisoners of Carceri wait eagerly for this time and search for these ellusive portals, but they are seldom discovered.

More rarely, and much more randomly, Carceri may enter into true conjunction with layers of the Abyss other than the Plain of Infinite Portals.

For a few months at the beginning of each year, in an event known as Forlorn, Carceri and the Gray Waste enter into true conjunction. The weather in Carceri becomes gloomy and gray, plants wilt, and everyone's mood becomes infused with sorrow and apathy. No new portals open from Carceri's end, but on a single day each year a few portals to Oinos may become passable without keys. Some years Forlorn combines with the Rotting.

Three months before Forlorn, Carceri enters into true conjunction with the Outlands in an event known as the Veiled. The weather becomes miserable and rainy, the terrain filled with mist, fog, and smog. During a single day, the portal to Curst becomes passable without a key. Few escape that way, because Curst is nearly as hard to leave as Carceri itself, but during that time the gate-town becomes flooded with Carcerians.

Only Othrys experiences seasons; the inner layers of Carceri are sheltered from planar conjunctions, although they may (very rarely) collide with odd layers of the Abyss.

Carceri only enters into true conjunction with the Material Plane once every 333 years. At that time, portals may open between the two planes, often in deep caverns and the hearts of dormant volcanoes.

Carceri has no season associated with the Astral Plane, however brief - it is too isolated and turned on itself. The only thoughts that breathe on its orbs come from within itself.

Gray Waste

Planes in conjunction: Carceri, Gehenna, Outlands, Astral, Material Plane

For about a quarter of the year (91 days, or 13 weeks), Oinos is dominated by a phenomenon known as Ironskies, when Carceri's planar traits (but not its color) bleed over into Oinos. For the next quarter, the time of Infernus dominates, as the planar traits of Gehenna bleed in along with sulfurous fumes and a terrible, oppressive, muggy heat.

The other two Glooms of the Waste come into true conjunction for the other two quarter-years. During the time of Deep Mourning, Pluton dominates, shrouding Oinos in darkness while Pluton receives some of Oinos' plagues. During the time of Spiritchill, Niflheim dominates, and Oinos experiences its equivalent of winter while Niflheim feels the plagues of Forlorn. Then Ironskies returns with its thick black clouds, razorvine, political tension, and paranoia, and the cycle begins again.

For the last four weeks of Spiritchill, the temperature becomes warmer and the fogs of Niflheim blend with the miserable rain, smog, and sleet of the Veiled, the time of true conjunction with the Outlands.

One of the three layers of Azzagrat was ripped from Niflheim, and the two layers still irregularly come into true conjunction. During that period, Niflheim experiences the Rotting and Azzagrat experiences Forlorn.

Limbo

Planes in conjunction: varies

Most of the time, Limbo is coterminous with the Astral Plane, Ysgard, Pandemonium, and the Outlands. Sometimes it isn't coterminous with any of these. Sometimes it's coterminous with the Elemental Plane of Water, or the Far Realm, or the 408th layer of the Abyss. It enters into true conjunction with random planes at random, into severance with other planes at random, and generally makes a mess of everyone's charts and orreries. Only a few artifact-level models, like the Great Orrery of the Modrons, can accurately predict Limbo's conjunctions - and even those often get it wrong. Planar aetherscopes are accurate only at a DC 20.

Gehenna

Planes in conjunction: Outlands, Hades, Baator, Astral, Material Plane

Gehenna's year has seven months of 52 days each. Each month has four weeks of 13 days.

The first month, Firetime, represents the time when Khalas, Mungoth, and Krangath are in true conjunction with Chamada. In Khalas, all the volcanoes become as furious on this layer as they normally are in Chamada. In Chamada, this month is known as Fire's Ebb, and the volcanoes actually calm down to approximately the same level Khalas normally experiences. In Mungoth, the cold volcanoes of the layer spark into life and magma flows at Khalas' normal rate, though the rest of the layer gets no warmer. In Krangath there is no obvious change, but the dead volcanoes of the layer become open portals to Chamada; much wandering through dark tunnels is required to make the journey, however.

The second month, Agony, represents the time when Mungoth is in true conjunction with the other furnaces. Ice and sleet fall from the void above all four layers, and biting cold is added to the torments of fire and darkness.

The third month, Shadowrule, represents the dominance of Krangath. The other furnaces are eclipsed, and are no longer visible in the sky. While the volcanoes continue to spew lava and ash, the lava streams no longer glow, and they flow invisibly through the darkness. In the city of Void's Edge in Khalas, the first day of Shadowrule is called the Day of Nighttides, and even artificial lights are snuffed out to allow all manner of debauchery to take place under cover of darkness.

The fourth month is Silverwinds, when the thought-winds of the Astral impinge upon the four furnaces (beginning in Khalas). Silver clouds blow above the furnaces, visible everywhere but Krangath, and in Khalas the infinite astral conduits can be seen twisting above them. Alien thoughts whisper through everyone's heads, and portals may change, vanish, or be created. Why this conjunction lasts for so long in Gehenna is unknown, but it is thought that the yugoloths have invited this season in order to better monitor the other planes.

After the silver clouds fade, the other neighboring planes begin to impinge. The end of Silverwinds marks the beginning of Forlorn, the long period of gloom and depression, where all activity slows down and the ultroloths typically merge with the plane in their period of hibernation. Even the light of the volcanoes takes on a grayish tint.

When the light of the volcanoes changes from orange-gray to hell-red, the month of Hecatomb has begun. This month is characterized by storms and flaming meteors from Avernus, though sacrifices to the gods or the ruling yugoloths can avert the worst storms.

The first week or so of the next month, the Veiled, is called the Perfumed Days in the city of Void's Edge. This is the time they celebrate the end of the nupperibo shipping season and their accompanying reek with perfumes and incense of all kinds until the smog gets too thick to enjoy it. Across the Fourfold Furnaces, the month of the Veiled is characterized by smog and pollution as the mists and rain of the Outlands combine with the volcanic fumes of Gehenna in the most terrible way. Visibility gets very short in all layers. When the smog is burnt away by an increase of volcanic activity in Khalas and Mungoth, the month of Firetime has begun again, and with it a new year. The smog remains for a few weeks longer in Krangath.

Gehenna enters into true conjunction with the Material Plane every 188 years. Natural portals to Khalas often open up in active volcanoes.

Baator

Planes in conjunction: Outlands, Gehenna, Acheron, Astral, Material Plane

Baator has 10 months of 35 days each, plus two extra weeks each year that are allocated at the discretion of the Ministry of Supply, which controls each baatezu's allotment of time. Officially, the government of Baator denies these weeks exist, so they are usually selected to coincide with activities that Baator also denies the existence of. Alternately, missing weeks can be stored up in order to provide plausible deniability for entire years (in at least one case, 297 years disappeared from the records at once).

Baator's ten months are as follows:

Zariel is the first month of Baator's official year. Although Bel has ruled in Zariel's place for centuries now tradition in Baator dies hard, and the first month still belongs to his predecessor.

Zariel is followed by Dispater, which is followed by Minauros, Belial, Fierana, Levistus, Malegard, Triel, Mephistopheles, and the Dark Month. There is little to distinguish one month from another on most of Baator's changeless layers. However, Avernus comes into true conjunction with a number of different planes. The first week of the year it is in true conjunction with the Astral Plane, the next two with Acheron, the next three with Gehenna, the next four with the Outlands, the next five with Acheron again, the next six with Gehenna, the next seven with the Outlands, the next eight with Acheron, the next nine with Gehenna, and the final seven with the Outlands again.

The Astral's dominance is associated with silver clouds and ghost-winds; Acheron's domination is associated with storms; Gehenna's influence brings sulfurous fumes and acid rains; the Outland's time brings mists, fog, and drizzle. The changing seasons are not actually dignified with names in Baator - only the names of the months are permitted to be used.

Baator falls into full conjunction with the Material Plane once every 66 years, its portals opening into places of iron and darkness.

Mechanus

Planes in conjunction: Outlands, Acheron, Arcadia, Astral, Material Plane

There were, until fairly recently, exactly eight planes with a heavy influence over Mechanus. Now one of the seasons seems to be missing, and no one can say why. The gears have been turned out of order.

Arcadia

Planes in conjunction: Outlands, Mechanus, Celestia, Astral, Material Plane

The seasons here are controlled by the Storm Kings. Arcadia rarely comes into true conjunction with other planes; as little as one day a year with Mechanus, the Outlands, and Lunia, and one day per century with the Material Plane.