Nirn

Nirn is largely known by otherworldly beings as Mundus, or the mortal plane. The exact reasons and specifics of Nirn's creation are largely debated; however, all agree that the deity Lorkhan inspired, and played a large role in, the creation of the watery planet known as Nirn. Two moons, Secunda and Masser, orbit Nirn. Metaphorically, they represent Lorkhan's sundered halves. Nirn orbits an unnamed sun, and is, so far, the only discovered planet in the solar system. The heavens beyond Nirn are star-filled. Astrology, a science of the planet's intelligent organisms, has been used to graph an attach spiritual meaning to these celestial bodies.

Creation myths
There are many theories on how he created Nirn; ranging from the other Aedra agreeing to willfully help, to Lorkhan tricking them into it. However, it is universally acknowledged that the Aedra gave their energy and power for it, and that the majority gave up on the project after realizing the cost, and that those who did not, became the Eight Divines, or the Earth Bones. In, Mankar Camoran proclaims that Nirn is possibly an extension of the realm of Oblivion.

Lunar activity
Two moons, Secunda and Masser, orbit Nirn. Metaphorically, they represent Lorkhan's sundered halves. Masser, Nirn's larger moon), revolves around Nirn. It can be spotted that in Oblivion, Secunda, Nirn's smaller moon, revolves around Masser. Thus, some opinions say that Masser is actually a planet, but since it is revolving around a planet, it could simply be a bi-revolving moon system.

Axial tilt and climate
It is never stated, but can be assumed, that Nirn's axial tilt is negligible, since days and nights remain more or less the same length throughout the year, even in the northern part of Skyrim. There also appears to be minimal variation in climate from month to month.

The northern regions are iced. The land of Atmora, far to the north of Skyrim is said to be primarily frozen plain. Skyrim, and by some extension, Bruma, are typically snowy, especially farther north, towards Winterhold and mages college there. Towards the center of the planet lies Elsweyr and Black Marsh, relatively tropical and warm locations.

Weather
Snow and rain are common forms of precipitation on Nirn. Certain areas within the mountainous tundras of Skyrim experience rare celestial weather called "Aurora".

Geography
The notably large continent on the planet is called Tamriel, which is where all of the Elder Scrolls games take place. With another similarly large continent to the east named Akavir, the landmasses are separated by the Padomaic Ocean, a massive saltwater body of water. In-land water bodies are fresh, low in sodium, and are drinkable.

To the North of Tamriel is the cold, barren land called Atmora, which is where the Nords of Tamriel hailed from. To the west of Tamriel lies Yokuda, which was the former homeland of the Redguards of Tamriel. To the southwest of Tamriel lies Pyandonea.

Tamriel
Tamriel is geographically interesting as it has mountains, tundras, cold deserts, hot deserts, swampy regions, grassland, tropical rainforests and an arguably large volcano. The diversity of biomes is unique as the hot desert is bordered by cold mountains to the north.

Tamriel also holds home to a series of islands called the Summerset Isles and is where the Altmer, or "High Elves", hail from.

Yokuda
Not much is known about Yokuda since it was nearly obliterated in a cataclysmic event, but it seems to have a dull, rocky, hilly, desert landscape. It is known to be the original home to the Redguards of Hammerfell.

Atmora
Atmora is a barren and freezing wasteland. It is this extreme cold that caused the water of the Sea of Ghosts that borders Tamriel and Atmora to become icy. This frozen land is also where the Nords of Skyrim are originally from, although not many trips back are made.

Akavir
Next to nothing is known about the geography of Akavir. The only thing known about Akavir is that it is the original home of dragons. The Blades, former dragon hunters, turned to serve Reman Cyrodiil in their search for a Dragonborn. These Blades were originally from Akavir, and their culture, although dying, persists in the fashion their instigated.

Pyandonea
Pyandonea is the island-continent located to the far southwest of Tamriel and home to the elusive Maormer. The island consists of dense rain forests which provide shelter for the southern water spirits.