The Night Shade of Greyhawk and the Hallowed Revenant Amphoras
According to the paper by Gary Holian in Oerth Journal, Oerth's circumference is about 42,024 km, and its radius measures 6,714 km, about 1% more than that of Earth. There is no flattening of the planet sphere due to rotation, and divine power is again hinted at.
Oerth has at least four continents, the largest of which is Oerik, lying mainly in the Northern Hemisphere. Southeast of Oerik lies the much-smaller landmass of Hepmonaland, lying in the tropics. Hyperboria, also called Telchuria (after Telchur, the god of winter), lies at the north pole, while an unnamed fourth continent lies in the southern hemisphere. Oerth is thought to have four oceans, including the Solnor Ocean, the Dramidj Ocean that circles Telchuria, the Ocean of Storms south of Oerik, and the Sea of Thunder encompassing Polaria.
Oerth also has a number of islands, the largest being Fireland in the northern Solnor, depicted on maps as being roughly half the size of Hepmonaland. Polaria is a chain of mountainous islands covered for at least part of the year by the southern polar ice cap.
Telchuria is an ice-covered continent at the north pole of Oerth. Telchuria is sometimes referred to as "High Boros" or "Hyborea."
It is possible that, in the depth of winter, a natural ice bridge forms between Telchuria and the Land of Black Ice.
Oerth in the "Solar" System
It takes exactly 24 hours for Oerth to make one revolution on its axis. Oerth lies at the center of Greyspace. Unlike most planets, Oerth does not orbit its sun, Liga. Instead, the sun, and all other planets in the crystal sphere, orbit Oerth. Thus, Greyspace houses a geosystem, rather than a solar system. Oerth's "moons," Celene (Kule) and Luna (Raenei), are in fact the first and second planets in the geosystem, with Liga being the third. From Oerth, planets beyond Liga appear to the naked eye as wandering stars.
Liga orbits the Oerth once every 364 days, thus the Oerthly year is slightly shorter than that on Earth. Luna has a 28 day lunar cycle, while Celene's cycle is 91 days.