Discworld: The eight seasons

Pratchett goes into a bit of detail about the physical appearance of the Discworld in this first book, mentioning facts which are never repeated.

For example on pg 11, he states that the Discworld rotates once every 800 days ("to distribute the weight fairly upon itds supportive pachderms). (How could the Discworld rotate? Granted that it's a disc resting on the backs of four giant elephants, there's no way it could!)

The disc also has a tiny orbiting sunlet.

"Since the disc's tiny orbiting sunlet maintains a fixed orbit while the majestic disc turns slowly beneath it, it will be readily deduced that a disc year consists not of four but of eight seasons.The summers are those times when the sun rises or sets at the nearest point on the rim, the winters those occasions when it rises or sets at a point around ninety degrees along the circumference.

Thus, in the lands around the Circle Sea, the year begins on Hogs' Watch Night, progresses through a Sppring Prime to its first midsummer (Small God's Eve) which is followed by the Autumn Prime and, straddling the half-year point of Crueltide, Winter Secundus (also known as Spindlewinter, since at this time the sun rises in the direction of spin..."