Nirn

 is referred to by otherworldly beings as the mortal plane. The exact reasons and specifics behind Nirn's creation are largely not known for certain. However, all agree that the deity Lorkhan and the Eight Divines played pivotal roles in the creation of the waterlogged planet. Two moons, Secunda and Masser, orbit Nirn. They are Lorkhan's sundered corpus. Nirn is the center of Mundus, which itself is the "hub" of The Elder Scrolls universe's "wheel." The heavens beyond Nirn are star-filled. These stars are holes or portals through Oblivion to Aetherius, and carry magical significance due to the beings which tore them open, the Magna Ge.

It is, of course, the Elder Scrolls equivalent of the planet Earth.

Creation myths
There are many theories on how Lorkhan 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, that the majority gave up on the project after realizing the cost, and that those who did not became the Eight Divines In, Mankar Camoran proclaims that Nirn is possibly an extension of the realm of Oblivion.

Lunar activity
Two moons, Secunda and Masser, orbit Nirn. They are Lorkhan's sundered corpus. Masser, Nirn's larger moon, revolves around Nirn. By observing the nighttime sky in and, it is revealed that Secunda, Nirn's smaller moon, revolves around Masser.

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 frigid. 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. Closer to the equator lies Elsweyr and Black Marsh, relatively tropical and warm locations.

Weather
Snow and rain are common forms of precipitation on Nirn. Certain areas in northern Tamriel, such as Skyrim and Solstheim, experience rare celestial weather called "Aurora".

Geography
The planet has a notably large continent, Tamriel, which is where all of the Elder Scrolls activity take place, with another similarly large continent to the east named Akavir. The land masses are separated by the Padomaic Ocean, a massive saline body of water.

The cold, barren land called Atmora is to the north of Tamriel, 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 south-west of Tamriel lies Pyandonea. It is unknown if these are the only continents, as there are very few maps or globes showing all of Nirn. The known Nirn (the part that has been currently mapped) is a mere 11 times smaller than Earth and since they both have very similar gravity it must mean that only a very small part of Nirn has been mapped.

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.

Also known as dawns beauty in the language of the Altmer, Tamriel also has an archipelago of islands called the Summerset Isles, which became the home of the Altmer, or "High Elves", after they abandoned their original homeland of Aldmeris.

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

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. It is known that the continent is split into four warring kingdoms, each boasting its own race: Tang Mo, Kamal, Ka Po' Tun, and Tsaesci. Akavir is known to have been a home to dragons. The Blades, originally from Akavir where they were known as the Dragonguard, but turned to serve Reman Cyrodiil in their search for a Dragonborn.

Pyandonea
Pyandonea is the island-continent located to the far south-west of Tamriel and home to the elusive Maormer. The island consists of dense rain forests which provide shelter for the southern water spirits. Due to its populace being Merrish, there is speculation that Pyandonea may in fact be part of Tamriel.

Thras
Thras, also known as the Coral Kingdom has been a powerful, antagonizing power against the Summerset Isles since before recorded time. The Sload may at one time have even called Summerset part of Thras.

Aldmeris
Little is known about Aldmeris (including if it still exists). The Altmer claim that this continent was the birthplace of both elves and mankind.

Trivia

 * 'Nirn' means 'Arena' in Ehlnofex.