June 21st (Solstice): The “Gates of Summer” (Tarnin Austa) is the Elven Midsummer festival which starts the prior night and anticipates the rising of the Anar, the Sun in the East, who is “steered” in the skies by a fiery Maia (meaning “Beautiful One”) named Arien.
In the Elven stories, the Sun was created by the last fruit from the female Golden Tree named Laurelin (whereas Isil, the Moon was created from the last flower from the male Silver Tree, Telperion, and “steered” in the skies by the Maia Tilion). The trees themselves (before their destruction by the Dark One) were created by Yavanna Kementari, Queen of the Earth and Giver of Fruits (in what could be seen as the “Elven Pantheon” that are collectively called the Valar). The Sun, Moon and Stars were all made by Varda Elentari, Queen of the Stars – the Elves deemed her their favorite of all of the Valar. She is the one in Lord of the Rings referred to as Lady Elbereth Gilthoniel, and her energies are very protective! She also created out of Telperion’s sap Valacirca, the Sickle of the Valar to keep the Dark One at bay – today, we know this star constellation as the Big Dipper.
The fullest description of Tarnin Austa is set in the hidden Elven city of Gondolin, as shown in this quote from JRR Tolkien’s Book II of the Lost Tales (aka HoME Vol. II):
“[…] and now at length is that great feast Tarnin Austa or the Gates of Summer near at hand. For know that on a night it was their custom to begin a solemn ceremony at midnight, continuing it even till the dawn of Tarnin Austa broke, and no voice was uttered in the city from midnight till the break of day, but the dawn they hailed with ancient songs.
“For years uncounted had the coming of summer thus been greeted with music of choirs, standing upon their gleaming eastern wall; and now comes even the night of vigil and the city is filled with silver lamps, while in the groves upon the new-leaved trees lights of jewelled colours swing, and low musics go along the ways, but no voice sings until the dawn.
“The sun has sunk beyond the hills and folk array them for the festival very gladly and eagerly — glancing in expectation to the East.”
For more information, see the “Loa” or the Elven Calendar post.