|Oerth, as depicted on the cover of the 3.5 Dungeon Master's Guide (2003). Art by Henry Higginbotham.|
|Planetary Body Type||Earth|
|Size||8,021.5 miles in diameter.|
|Rotational Period||24 hours|
|Orbital Period||N/A; Liga orbits Oerth every 364 days|
|Satellites||Celene (Kule) and Luna (Raenei); technically, as the prime, all planets in Greyspace are Oerth's satellites.|
|Distance from Primary||0 (prime)|
|Native Inhabitants||Humans, elves, dwarves, orcs, halflings, gnomes, goblinoids, many others.|
Oerth is the name of the planet on which the World of Greyhawk campaign setting is located. Oerth has an axial tilt of 30 degrees, which should cause greater extremes of temperature in different seasons but for wizardly and divine magic shifting weather patterns to be more favorable to the populace (at least the god-fearing folks).
Oerth has 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 the archipelago known as Fireland in the northern Solnor. Polaria is a chain of mountainous islands covered for at least part of the year by the southern polar ice cap.
The easternmost part of Oerik, the Flanaess, has received the lion's share of detail, though Hepmonaland has received significant attention. Western Oerik was the setting for Wizards of the Coast's original miniature line, Chainmail, which was cancelled in 2002.
Author Frank Mentzer, in a series of early modules, added a small territory called New Empyrea to the world across the Solnor Ocean from the Flanaess, but it has not been mentioned in subsequent Greyhawk products.
Oerth's planetary 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 is geocentric. Oerth's "moons," Celene (Kule) and Luna (Raenei), are in fact the first and second planets in the system, 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.
In a 1984 interview for Polyhedron Newszine, Gary Gygax revealed several "alternate Oerths" while explaining the setting for his Heroes Challenge game books, co-written with author Flint Dille and published under the aegis of the Dungeons & Dragons Entertainment Corporation by the Wanderer Book division of Simon & Schuster.
"By the way, action takes place on Yarth, a place somewhat similar to Oerth, the setting of Greyhawk, et al. It has fewer magical properties than Oerth but more than Earth. It is not impossible that additional works will be contracted for in months to come, action being set on Yarth or perhaps another alternate world, Aerth. On Earth, magic is virtually non-existent. On Uerth, dweomers are weak, chancy things. Yarth has a sprinkling of things magical, and Oerth is pure magic."
Other references to these alternate Oerths appear in the Gord the Rogue short story anthology Night Arrant as well as in Gygax's Epic of Ærth campaign setting for the Dangerous Journeys roleplaying game.
The five parallel worlds of Oerth—Oerth, Aerth, Uerth, Yarth, and Earth—were mentioned in the 3rd Edition adventure Expedition to the Ruins of Greyhawk and thus found their way into 3rd edition canon.
- Gygax, Gary. Epic of Ærth. Bloomington, IL: GDW, 1992.
- -----. Night Arrant (New Infinities, 1987).
- -----. "Why Gargoyles Don't Have Wings but Should." Polyhedron #21. Lake Geneva, WI: TSR, 1984.
- -----. World of Greyhawk Fantasy Game Setting. Lake Geneva, WI: TSR, 1983.
- Holian, Gary. "Measuring up the Oerth." Oerth Journal #4. Council of Greyhawk, 1996. Available online:
- Holian, Gary, Erik Mona, Sean K Reynolds, and Frederick Weining. Living Greyhawk Gazetteer. Renton, WA: Wizards of the Coast, 2000.
- Mentzer, Frank. Doc's Island. Lake Geneva, WI: TSR Hobbies, 1983.
- -----. Egg of the Phoenix. Lake Geneva, WI: TSR Hobbies, 1982.
- -----. The Investigation of Hydell. Lake Geneva, WI: TSR Hobbies, 1982.
- -----. To the Aid of Falx. Lake Geneva, WI: TSR Hobbies, 1982.
- Moore, Roger E. Greyhawk: The Adventure Begins. Renton, WA: TSR, 1998.
- -----. "Oerth from the Ground Up." Oerth Journal #3. Council of Greyhawk, 1996. Available online:
- Williams, Skip, and David C. Sutherland III. "Beyond the Flanaess." Dragon Annual #1. Lake Geneva, WI: TSR, 1996.