The sun and the moon

[Knightmare]

The sun and the moon of Faerún, what are their true names, does anyone know? Or, are they just refered to by our RL names?

Is there any specific "must know" lore to them?

[Maecius]

The moon is named Selûne. The sun is just "the sun."

An introduction to the planet of Abeir-Toril and its solar system:

Abeir-Toril is an Earth-sized planet dominated by a large continent in its northern hemisphere as well as a number of other large landmasses scattered about its surface. This northern continent is called Faerûn in the west, Kara-Tur in the east, and Zakhara in the south. It is the primary purpose of this tome to deal with the western portion of this huge landmass, in particular the region in Faerûn between the Sword Coast and the Inner Sea.

Abeir-Toril has a single satellite, Selûne (also the name of the goddess of the night sky and navigation). This luminous, heavenly body is followed in its path across the sky by a collection of shining shards, called the Tears of Selûne. These tears are said to be nothing more than a cluster of ordinary asteroids and debris that trail the moon in its path, yet the Tears remain reflective and bright even when the moon is new in the sky.

In addition to the moon, there are seven visible planets that wander against the star-misted sky. They are dusky Anadia, green Coliar, blue Karpri and Chandos, ringed Glyth, odd-appearing Garden, and disk-shaped H'Catha. All follow regular paths around the sun. The stars are distant and eternal, and form themselves into patterns and constellations that each culture names according to its own desires.

A Torillian year is 365 days of 24 hours each. An orbit of Selûne is roughly 30 days.

Source: Forgotten Realms Campaign Setting (Second Edition), 4.