Two sisters cast adrift in the Cosmic void—trailing manes and tails of stellar radiance—curled and slumbering, were ever intertwined.
The elder sister, her surface as white as a dwarf, was called Celestia, and she embodied the day.
The younger was named Luna, and called the ‘Young Moon,’ trapped as she was in her sister’s orbit.
Luna embodied the gentle night, and while Celestia was enwreathed in a rainbow of color Luna nested in nebulous darkness, within which dwelt the soft light of distant stars.
Colonists braving the void between branches would sometimes spot Celestia’s rainbow and navigate by it, finding their way to where the sisters lazily drifted.
Invariably the visitors would settle upon Celestia’s chalky flanks, her high-albedo hindquarters stark against the void.
In time, the disparate settlements established trade agreements, which led to rapid expansion. When the borders of the settlements blurred, the leaders of the foremost colonies, being the Unicorns and Pegasi—which began to appear among the first generation to be born upon the Flanks—and the apparently unaltered masses of the Dispossessed, met to determine the fate of Celestian civilization.
Together they drew up a charter and founded a city that unified their lands under a single banner, and that city was called Solaris, known later as the First of the Marks.
Not all found the crowded streets and rampant sprawl to their liking, however. A band of sages set off to found the Dock Settlement of Æsir-Bilröst, guided by the flowing light of the Rainbow Tail.
Others, seeking claim struck out toward the White Mountains, but ultimately chose to settle along the Seam where they harvested the sweet and glittery fluid that at times secreted from within.
Others still abandoned Celestia altogether, leaving in their ancient vessels to seek refuge on the shadowy flanks of the Young Moon. Though their exile was self imposed, they took to calling themselves Outcasts and looked upon the Mark with distaste. They built their holds all in a line, curved like a crescent scar.
Meanwhile Æsir-Bilröst prospered, establishing a trade agreement with Solaris that would eventually become an alliance. By the time the holds of the Outcasts were completed the ‘Free-City’ had produced a number of ‘Seers,’ enlightened by their lofty position above the Tail.
One such individual was called Starswirl the Young, and was by accounts a prodigy. It was he who witnessed the baleful glow ignite across the scar, recognizing the danger before any-pony else.
When the Young Moon next arose so did the Nightmare. From the holds of the Outcasts came a cannonade of balefire meant to decimate Solaris, yet Starswirl was prepared.
The seers, using their singular horns which Starswirl had come to believe were an inherited aspect from Sol Celestia, they magically coaxed the tail to flow above the Mark, shielding the city from the barrage and saving the lives of many.
Soon after, Starswirl and a handful of followers made pilgrimage to the Mark. Under their instruction the city was fortified with wards and weapons of Starswirl’s own design, so that when the Moon came around again Solaris was able to retaliate, disabling a number of hostile settlements.
During the exchange Starswirl glimpsed the fluttering eyelids of the Young Moon, trying to wake from the tormenting Nightmare, and realized that to end this conflict Luna’s long sleep must come to an end.
Rumors had reached the Mark regarding ancient machines from a now-vanished civilization, one that predated their own brief history. Seeing no better option, Starswirl sought out the ruins, and with him came a retinue of builders and excavators from among the Dispossessed. The procession made their trek beyond the Point of Hip to the underside of the Barrel, coming upon an antique apparatus built about the White Mountains.
In the valley between the Mountains and the edge of the Seam they set up camp and established communications with the miners of the Seam. There the Tail could be seen from beneath, and with this new perspective Starswirl glimpsed something previously unseen within it: a recollection, providing insight into the purpose of the ancient mesh.
The device was intended to adjust Celestia’s rotation, and though complete it was never used, the finer components left to decay, yet with Starswirl’s guidance the Dispossessed were able to restore it to working condition; it merely lacked power.
Many workers from the Seam had taken notice of Starswirl’s project, pitching in with the restoration. When called upon to contribute a measure of the glittery fluid they mined they did not disappoint.
Yet, Starswirl was hesitant to proceed. Wanting to be sure, he turned his gaze upward to Celestia’s Radiant Mane. What he found was not glimpsed within the rainbow, but behind it.
Upon Celestia’s horn was a second, ring-like device, glowing with purple runes.
The command was given then to activate the machine, which shared the same glow. The mesh tightened, pressing in on the mountains from all around, throttling them from the base until the peaks erupted with volcanic milk. The stars began to spin, and as they did a portal appeared, through which could be seen the linked apparatus. Starswirl realized what he must do, stepping through the gate and emerging on the ridged surface of Celestia’s horn.
From this dizzying vantage he watched as Celestia revolved, turning to face her sleeping sister, who’s horn bore an identical artifact. Like magnets, the two rings drew toward one another, binding their horns together.
Celestia’s eyes fluttered open, and for the first time in centuries she beheld her sister. She saw her pained expression, and raged.
Mane and tail flared brightly. Within the burning rainbow Starswirl saw a fragment of a future that would hinge on either a Morning or Evening star.
The light burned away the Outcast holds and lead Luna to waking. She stared into her sister’s eyes and tears began to well in her own, but before she could cry Celestia kissed her. As Starswirl looked on, he realized a new age had begun.
Author's Note
This took way longer than I had expected. The original draft was much too long, and it took me awhile to trim it down, which I did at a leisurely pace while working on other things. 
