Moon of Selûne

Selûne, or Leira to some civilisations, is Toril's only natural moon. Named after the goddess of the Heavens, it orbits Toril and is visible to all civilisations across the face of the planet. As one of the largest divine bodies on the prime material plane, it is highly magical, coated in a magically induced atmospheric shell which can support some extra-terrestrial life, and is drawn on by various divine spell casters. As such, it is highly central to many religious doctrines of the mortal world.

Geography

Selûne was about 2,000 miles across and was located 183,000 miles away from Toril. Since the revolution and rotation period of Selûne's orbit around Toril were the same, only one side of the of the moon faced Toril, while the far side could never be seen from the planet. The surface of Selûne had enormous lakes and two large seas. Three large mountain ranges ran the surface of the moon from North to South. The mountaintops of the 12 tallest mountains were constantly molten and gathered heat from the sun during the moon's 15-day-long day. As they cooled down, they shone an incandescent light that was bright enough to read by during most of the moon's 15-day-long night.
Selûne had a remarkably stable temperature, thanks to its magical blanket. Except for the hot mountain tops, the surface of the entire moon was relatively cool, although temperatures never dropped below freezing.

Lunar Phases

Selûne orbits Toril on an wide elliptical path every 28 days, 10 of which are spent close to the planet and 18 far from the planet. The days where the moon is closer result in an eclipse every four months, and larger tides on the shores of the hemisphere the moon is closer too. The days where the moon is further away result in calmer and more stable tides throughout the day, and a fainter moon in the sky. For those who magic lunar magic, the phases of the moon impacted the potency of their spells, peaking in the full moon and dipping in the new moon.
The phases of the moon can be seen by the art below

The Tears of Selûne

Orbiting Selûne is a large celestial body dubbed "Selûne tears", a large asteroid cluster visible from Toril, which appears to follow Selûne along its path around the planet. There are hundreds of them, trailing the moon and orbiting one another. Several are home to air pockets and caves which are home to various extra-planar and void-breathing bodies.