Isil the Sheen was the name given by the Vanyar to the Vessel of the Moon, created from the last flower of Telperion. He cherishes the memory of the Elves.

Tilion was chosen to guide the Moon. When he first took the Moon into the skies, many things stirred and woke that had waited long in the sleep of Yavanna. Fingolfin blew his silver trumpets and began his march into Middle-earth. The Moon traversed the sky 7 times before Arien and Anar were released into the Heavens.

Tilion was wayward in his course and speed, and he was ever drawn towards the brightness and splendour of Arien. However, the flame of Anar scorched him, and the island of the Moon was darkened.

After Isil's journey through the sky, Tilion did not linger long in Valinor, but would pass swiftly over the west and plunged into the chasm beyond the Outer Sea, making his own way among the caves and caverns at the roots of Arda. There he would wander long, and sometimes would return late into the sky.
Encyclopedia entry originally written by atalante_star