Long, long ago, in the magical kingdom of Equestria, the land was ruled by two immortal and ageless alicorn sisters.

The elder sister, Celestia, was beloved across the land for her kindness and wisdom. As radiant as the dawn, she raised and lowered the sun each day, blessing her little ponies with its life-giving warmth.

The younger sister, Luna, was shy and mysterious. Rather than bask in the light of day, she raised and lowered the moon each night. She placed the stars in the sky to guide those who journeyed in darkness, and while she rarely held court, Luna guarded the dreams of her little ponies as they slumbered.

Alas, while the royal pony sisters were revered by their subjects, there were others who sought their destruction. Eclipse, a sinister fiend that could only dwell in shadow, sought to bring an end to both the day and the night that the sisters watched over.

In the shadow of moonlight and the flickering of torches, it crept upon Luna one night while the rest of the castle slept. It whispered in her ear, telling her that she was not as beloved as her sister. That her nightly labors went unappreciated by her little ponies. This awoke a spark of envy inside her, casting a shadow within her heart which Eclipse seized upon.

Eclipse burrowed its way into Princess Luna's heart, seizing control of her body and magic. With this stolen power, it commanded the moon to rise in the middle of Celestia's day, placing it between the elder sister's sun and the realm of Harmonia, casting the land into a shadowy fugue state, neither day nor night.

When Celestia discovered what had befallen her sister, her fury knew no bounds. Wielding the most powerful magic known to ponykind, the Elements of Harmony, she faced Eclipse and turned their power upon her possessed sister, hoping to cleanse Luna of the fiend's tainted presence.

But Eclipse was as cunning as it was vile. It could not withstand the power of the Elements, so it struck at the heart of their wielder. Speaking in Luna's voice, Eclipse screamed in agony, begging to Celestia to make the pain stop.

No matter how boundless Celestia's wrath toward Eclipse might have been, it was but a pale shadow compared to the love and compassion that she felt for her sister. Her will faltered, and in a single moment, rather than risk harming Luna, she severed her connection to the Elements of Harmony just as they succeeded in separating Luna from Eclipse. Their work incomplete, both Luna and the Elements fell, inert, to the earth.

And so it was that Eclipse escaped. Still possessing Luna's hold over the moon, Eclipse continued to hold all of Harmonia in its shadow for months on end. Celestia's forces pursued the fiend from one end of Equestria to the other, but with the land cast in shadow, it was free to travel as it wished. Free to stalk and possess other creatures in order to hide from sight, then abandon its stolen bodies, leaving a trail of hollow, barely-alive husks in its wake.

In the end, Eclipse was not caught by its pursuers, but through a desperate ploy. Princess Celestia, mourning the sister who was trapped in unending slumber, offered up her stewardship of the sun in exchange for a chance to be reunited with Luna.

For Eclipse, the opportunity to command both the sun and the moon at once proved itself an irresistible lure. And so the power-hungry shadow appeared before Celestia, though it had no intention of dealing in good faith with the princess. No, Eclipse intended to steal Celestia's power for itself through the shadows of grief and anguish which festered in her heart.

But Celestia was wise, and knew that with no reason to fear the Elements of Harmony, Eclipse would seek to simply take that which it desired. Therefore, using herself as the lure, she set a trap for the shadow. The moment that it attempted to enter her heart, Dame Sungleam the knight and Nyx the thestral, heroes steadfastly loyal to Celestia and Luna, swooped in to stand against Eclipse.

Eclipse raged at the chance for absolute power that it had been denied, but with the bait dangling so close at hoof, it chose to do battle rather than flee. The fight was hard for the ponies who stood against Eclipse, but they met the shadow blow for blow. In the end, the day was won when Celestia, summoning every bit of strength that she could muster, banished Eclipse to the moon's shadow before moving the celestial bodies apart from one another.

But although the battle was won, it was not without grave cost. Sungleam was struck down by Eclipse, and laid to rest in a manner befitting a royal knight. Princess Luna failed to awaken despite Eclipse's defeat and remained trapped in an eternal slumber, neither dead nor truly alive. To ensure that she was kept safe, her body was secreted away to a hidden resting place in the hopes that she would one day return to the waking world.

As for Princess Celestia, she was grievously wounded in the battle, struck by a blow which shattered her immortality. As the centuries have passed, she has ruled over Equestria with kindness and wisdom, growing older and older with the passage of time, however slowly.

Despite this, the princess has not given up hope of seeing her sister again. As time passed, ponies far and wide have spoken of meeting the princess of the night as they slumbered, a phantom wandering adrift through the land of dreams. And so it was that Princess Celestia decreed that each year, on the anniversary of Eclipse's banishment, the ponies of Equestria decorate themselves and their homes in the guise of dreams and join in celebration of Luna's nights.

It is hoped that by doing so, the border between the dreaming and waking realms will thin, their revelries guiding the fallen princess back from her endless slumber.

Perhaps, if all of the ponies of Equestria try very, very hard to reach her, the next Waking Night will bring Princess Luna back to us.