The Discworld is a flat planet carried on the backs of four giant elephants - Berilia, Tubul, Great T'Phon and Jerakeen - which in turn stand upon the pock-marked shell of the star turtle Great A'Tuin. It exists right on the edge of Reality, and as such 'the least little thing can break through from the other side'.
The Disc is about ten thousand miles across (as proved by Ephebian philosopher Expletius). It;s about thirty miles thick at the Rim, but increasingly thicker near the centre (the Hub), maybe to hold an internal layer of molten rock, enabling the Disc's continental plates to move. How the molten state would be maintained is one of the two great mysteries of the Disc; the other would be how come, even though all the water on the planet is constantly falling off the Rim as the Rimfall, it is always replaced. One theory is that it's all done by Magic - vast amounts of the magical metal Octiron under pressure. This would explain the heat and the Discworld's vast magical field.
In some ways, the Disc's geology is fairly similar to our own world. The continents have certainly moved (possibly on little wheels, if the molten rock theory is put to one side for a minute).
Several hundred million years ago, the Disc's continents were arranged in one supercontinent, Pangola. The supercontinent was then hit by an unexpected meteorite (which some claim was the legendary Fifth Elephant, killing off most of the life on the Disc and splitting the landmass in two. It may also have been this that caused the Disc to change its direction if spin (this happens every hundred thousand years or so. No-one knows why, but it may have something to do with the comfort of the elephants).
About one hundred million years before the present, the Disc entered the perioud known as the Borassic Era, named after the wizard Venter Borass. By then, Pangola had split into two smaller continents, Howondaland and Lauragatea. The mountain ranges of the Disc were raised at about this time, by what has gone down in Disc history as 'a generally confused banging-about' as the world's spin direction changed.
Thirty million years before the present, Lauragatea lost the smaller (and deeply mysterious) continent of XXXX. Borass held that it had 'wandered off by itself, in search of the geographical equivalent of a nice cool drink.'
The Discworld as we know itEdit
The Disc apparently gives the impression, when seen from space, that the Creator had designed it specifically to be seen from above. From such a vantage point, you can really appreciate the thirty thousand mile circumference (one-third of which is guarded by the Circumfence to stop sailors from falling off the world, a more common problem than might be imagined).
Its sun (considered by some to be more of a sunlet, anyway) has a fixed elliptical orbit, taking about eight hundred days to come full circle. Owing to the rather cramped and inefficient astronomical arrangements (the Disc is the only place in the multiverse where an elephant sometimes needs to cock its leg to let the sun past), the small moon shines with its own light.
The effect of this is that the 'spin year' has two of each season - two winters, two summers, etc. But this is very much a purist's view of the calender, and most people deal quite sensibly with half years; maybe the sun rises on different sides as you face the Hub, but other than that, they follow the natural seasonal cycle. You plough, you sow, it grows, you harvest. That's a year. No matter what some daft old bugger with a pointy hat in Ankh-Morpork says.
The Disc week has eight days; the normal Earth seven, and Octeday. Hence the common phrase, 'we pretty much work 24/8 around here...'
The Hub is the equivalent of our polar regions - plenty of snow, ice and permafrosted mountains - while the Rim is similar to equatorial oceans - plenty of sunny islands and balmy days.
The Discworld seems to have four major landmasses:
- The Unnamed Continent in the middle of the Disc
- The Counterweight Continent, AKA 'The Aurient'
- XXXX, also spelt as Ecksecksecksecks and also known as Fourecks.
It has already been said that the Discworld exists right on the edge of Reality. It clearly should not exist. Planets are not naturally flat and turtles do not grow to more than ten thousand miles across, unless people have been getting really careless with genetic engineering.
Because it is right on the edge of reality, as well as the normal things (gravity, cause-and-effect, eventuality, etc., etc.), Discworld has a few little extras to physics.
- Life Force,
- The Power of Metaphor and Belief,
- Narrative Causality.
- The entire Discworld Series. That's more or less the point.