Tilion, the Huntsman of the Silver Bow, was chosen by the Valar to be the steersman of the Moon. He was also known as the ‘Horned’.
Originally, he was a servant of Oromë, hunting through the woods with his silver bow. He loved silver, and when he wished to rest, he would lie and dream by the pools of Estë in Lórien, bathing in Telperion’s flickering beams.
When the time came to appoint a guardian of the last silver flower of Telperion, Tilion begged for the task. The vessel for the moon, Isil, was wrought before that of the sun, and so the moon rose into the sky first, and became the elder of the two new lights. Tilion had traversed the skies seven times before Anar and Arien were released into the heavens.
Initially, it was Varda’s intention to have the sun and the moon working somewhat like the Two Trees, so that they would pass in their course, mingling their lights, in the middle of the Earth. But Tilion was erratic in his course, and uncertain in his speed, and he sought to come close to Arien – being drawn towards the Sun by her splendour. However, the flame of Anar scorched him, and the Island of the Moon became darkened.
Lórien and Estë beseeched Varda to change the vessels’ courses, as sleep and rest had been banished from the Earth. Varda then created a period each day when the Earth would have shadows and half-light. After his turn over the skies, Tilion would rush through Valinor, making his way to the chasm beyond the Outer Sea. There he would plunge into it, finding his way back to the skies through the caves and caverns at the roots of Arda.
But Tilion still remained uncertain in his pace and course, and he was ever be drawn to Arien, so that on some days both the sun and the moon can be seen together in the skies. At other times, he came so close to her that his shadow cut off her brightness and there was a darkness during the day.
Melkor hated the brightness of the lights, and while he dared not attack Arien, he sent spirits of shadow against Tilion, but after a series of struggles Tilion was victorious. However, the pursuit of darkness ever continued but Tilion was always victorious, even though darkness overtook him on occasion (presumably a reference to lunar eclipses).
Notes from HoME
In The Lost Road it states that Tilion loved Arien, but as she wished to remain virgin and alone, Tilion pursued her in vain.
Also in that book, there is also a wonderful paragraph describing Tilion’s first journey through the skies:
“Then for a while the world had moonlight, and many creatures stirred and woke that had waited long in the dark; but many of the stars fled affrighted, and Tilion the bowman wandered from his path pursuing them; and some plunged in the chasm and sought refuge at the roots of the earth.”
An alternative version of the mythology was given in a series of notes from Morgoth’s Ring. There the Moon was created long after the Sun, and was created by the Valar to counteract the night’s darkness in which Melkor worked his mischief. Melkor then gathered to himself spirits of cold, and assailed the Moon. Tilion was driven out, and the Moon became steerless and cold. After the death of the Two Trees, Tilion returned to the Moon, which then became ever after an enemy of Melkor and creatures of the night.