Plexus

The Plexus refers to the cosmology of the material plane. In short, it is the "glue" that holds the material plane in place. Scholars have studied its complex nature for centuries.

Overview
There are various models that have been constructed by scholars to explain the Plexus. Generally, it is thought of a cosmic weave: a sort of mostly-invisible tapestry holding the material plane together. The heart of the material plane is Aål, the burning star named after the Firstborn God. This is thought to be the pivot of the Plexus, around which all other components revolve. Spaced around the sun are the various plexic anchors (planets), as well as the non-anchor planets Noctis and Equis. The extent of the Plexus is believed to form a spherical shell around Aål, which forms the boundaries of the material plane. Beyond those boundaries lies unrefined Chaos.

Plexic Anchors
The various planets around the sun, except for Noctis and Equis (possibly), are called plexic anchors. They are the points at which the material plane is tied to other major planes. It is generally believed that the gods created their own dominions somewhere out in Chaos, and joined them to the material plane through the planets. There are three schools of thought about what the anchors actually are, but without some means of space travel, it is impossible to determine which of these theories is correct.
 * One theory posits that the plexic anchors are planets in the same sense as Noctis and Equis, but have an ethereal connection to their respective planes. Landing on them shouldn't transport the lander anywhere outside the material plane, but when the anchors cease to exist, their connection to their plane and any related High Magic is lost to the material plane. This is the most common theory on Equis. The main flaw in this theory is that it does not account for the continued High birth magic-infused nature of the shattered Jana stones, even after the connection to the Cradle of Creation was rendered inert.
 * Another popular theory states that the plexic anchors are just "color veils," spherical portals to their respective planes with no physical presence. It is the most commonly-held theory on Noctis. The main flaw in this theory is that it does not account for the physical forms of the moons, such as during the Skyshatter when the Lockean moon broke apart and bombarded Equis.
 * The third theory, which is slowly gaining popularity in both worlds, is a hybrid which states that the plexic anchors are somehow both portals and solid masses. Numerous variations exist, including the idea that the anchors "bounce" back and forth from portal and solid state, that they are simultaneously both, or that they are one or the other but can be forced to change form.

Inner Anchors
There are two inner anchors, which are the planets closest to Aål. One corresponds to the Plane of Order, and the other to the Fluid Nothing. Their orbits are the same, though on opposing sides.

Elemental Anchors
After the inner anchors, the next planets nearest to Aål correspond to the planes of the four basic elements: the Floating Ocean, the Boundless Sky, the Infernis, and the Plane of Earth. Uniquely, the elemental anchors do not seem to orbit Aål at all. Indeed, they never move, but rather are fixed in space in a roughly square shape. Diametrically opposed elements (fire and water; earth and air) are on opposite corners of the square. As Equis and Noctis orbit Aål they move closer to each planet at various points of the year, causing effects related to the plane the planets are closest to at any given time. including stronger High Magic for that element and weaker magic for the opposing element. In the same vein, travel to the closest elemental plane is easier, and travel to the farthest is harder.

The Three Sisters
Equis and Noctis once had three moons, but only two still remain. These are the Janan and Lefan moons. The Janan moon is in shambles since the Age of Creation, and the Lockean moon was destroyed completely during the Skyshatter. The three moons orbit Equis and Noctis in a figure-eight pattern. All Three Sisters are (or were) anchors for the dominions of their respective goddesses.

Outer Anchors
A number of planets orbit Aål beyond the orbit of Equis and Noctis. These are referred to as the outer anchors.

Transient Anchors
Some anchors exhibit a strange activity: they appear and disappear completely from the Plexus, sometimes in patterned intervals, and sometimes seemingly at random. It is unknown as yet what causes this shifting.

Unanchored Planes
Some planes are known to exist which are not anchored in the Plexus. The most notable of these are the Brilliant Sanctum, the Eternal Void, and the Grey Demesne: the planes of Light, Dark, and Shadow respectively. Rather than having plexic anchors, the planes of light and dark are "anchored" wherever there is illumination or darkness, respectively, and shadow is ubiquitous.

A few others are known, belonging generally to lesser gods. These have thus far only been accessed by passing through another intermediate plane first, such as the Boundless Sky (which allows for relatively easy planar travel).

Plexic Weave
The plexic weave is the fabric joining the anchors together. It is a web of complicated connections which can be thought of as threads of magic, running between Equis, Noctis, and the various anchors. Most inter-planar portals take advantage of these threads, traveling along them to enter other planes.

One type of high magic -- the kind most commonly used by mortals -- also uses the threads. The Weavers, the group that first developed this sort of High Magic, visualized their craft as pulling on the threads to obtain power. This kind of High Magic actually makes small, temporary holes in the plexic weave, and pulls the power released from this act to produce magic.

Tear in the Plexus
At one point, a tear in the plexic weave appeared, forming a rift. The result was an interruption in the relatively ordered flow of power, causing chaotic storms of High Magic to run rampant throughout the material plane. During this time, some mortals obtained High Magic "naturally" for the first time in history, beginning with Caius Mastis of Korbath.

Though the tear was eventually repaired and the plexic weave restored to order by Skool, observant mortals calling themselves the Weavers discovered a way to slightly manipulate the weave themselves. This gave rise to the discipline of wizardry, High Magic that does not require solitary dedication to a particular school of magic.