The light slowly dimmed as the sun crossed the horizon, leaving behind a red glow on the sky as a final plea to the world. "Don't forget me in the dark," it said. "I will be back tomorrow."
Celestia didn't know that it would be, should the worst come to pass. Tomorrow morning, if tomorrow morning ever came, would be the thousandth Summer Sun Celebration since that fateful night when she had been forced to seal her sister away.
Possibly forever, she had thought. That had been until Candle Wind, a pegasus with the very rare talent of understanding what dreams could tell ponies about the future, came to her with a prophecy. On the thousandth anniversary of Nightmare Moon's banishment, he had claimed, the stars would aid in her escape. Not all dreams told of the future, Celestia knew, but he had been certain this had been one such dream.
Candle Wind had been dead for over eight centuries now, but his words had left a lasting impression on Celestia. Where once she had been empty and cold without Luna by her side, she had begun to foster a spark of hope in the midst of that cold cave of her heart where Luna should be. The nightmares and guilt had continued plaguing her, but she had something to hold on to, a light in the distance to look towards as she trudged through the tunnel that had been the last one thousand years.
Tonight would be the night. She would either see her sister again or have that hope crushed forever more.
But only after the night came. Lowering the sun had cast the Royal Canterlot Garden into nearly total darkness as she took the day away without bringing the nighttime in. Only the lanterns along the garden's paths shone dim lights on the statues surrounding her.
Moving the moon was harder for Celestia than moving the sun, since it was not where her talent laid. She was more exhausted than usual from the day's royal duties, and that, she told herself, was why she hadn't moved both heavenly bodies at once tonight.
Unfortunately, she didn't buy it. The wisdom of a long life could be a curse sometimes. No, she was hesitating.
Why? She had been looking forward to this night for eight hundred and fifty-seven years. Why was she not jumping at the chance to raise the moon and bring in the night one last time, finally reaching the exit of that all too lengthy tunnel?
She knew why. A thousand years on one's own, as the only pony who wasn't there and gone in a flash, left one with plenty of time for introspection, and with introspection came a solid understanding of your own behaviors. Denial was hard when all you had to pass the time was ruling, thinking and cake.
The truth was, she was afraid of the exit. The tunnel was a known quantity. It was dark and straight, with nowhere to go but forward, each step the same, the light of the exit close enough to seek to but too far away to reach. But what laid behind the exit, assuming it even was an exit at all?
Celestia didn't know if Luna would return as herself, or as Nightmare Moon. Historians describing the prophecy had assumed the latter, and were very likely right to do so. She had prepared as best she could for that scenario, sending Twilight Sparkle to find the Elements of Harmony.
Twilight was unaware of both of the true purposes of her excursion, of course, but as Celestia lived on, ponies became more and more predictable. She would make friends in Ponyville, almost certainly with a group of young mares who embodied the Elements just like Twilight had the potential to. If Nightmare Moon did return and prove unable to be reasoned with, there would be nothing Celestia could do. Twilight and her friends would have to wield the Elements against her as Celestia once so foolishly did.
Whatever they might do to Luna. Celestia could wait another thousand years if she had to, she told herself, and knew she was lying again. She was really beginning to hate her own wisdom.
She looked at the dim shadows playing on the gaping stone face in front of her as the fireflies shifted in the nearest lanterns.
Sometimes, when Celestia was feeling nostalgic for her time with Luna, she would go see the statue that had once been their greatest enemy. This evening, she had come here to bring in the night, refusing to acknowledge why. She knew why.
The statue of Discord was a fossil, morbid as that may be. Solid, petrified evidence of a time when Celestia and Luna had stood together as friends, as sisters. He was proof that she wasn't going mad, proof that once upon a time, the fearsome Nightmare Moon really had been the good Princess Luna. An enemy long defeated and a sister long lost.
One of them would return tonight, if Candle Wind had been correct.
She could hardly bear thinking of the possibility that he hadn't been. What if the night passed and nothing happened? What then, when she had to raise the sun and bring an end to the night that should have brought her sister back? She would have to do it with a smile – tomorrow was the Summer Sun Celebration, the one day of the year when raising the sun was a performance. Her subjects needed their Princess to display her sunny side tomorrow.
Normally, Celestia was good at keeping her royal poker face during duties she did not enjoy, but if she had to celebrate tomorrow's dawn without having seen Luna, or even Nightmare Moon, she wasn't sure she could.
She felt tears running down her cheeks. How long had she been crying?
There was no use in taking her sorrows in advance, she knew. No more than there was in delaying the bringing of the night, and while that might buy Twilight a few minutes, that was but another excuse.
Celestia cursed her wisdom once more as she finally lit up her horn and grabbed the moon in her magic. Tears continued streaming as the slowest moonrise in recorded history unfolded before her and the dark shape of an alicorn's head came into view.
She stood before the light at the end of the tunnel, and now all that was left to do was wait. Time would tell if it really was an exit, but the hours ahead of her would feel just as long as the thousand years behind her.
Drying her eyes with her hooves, she turned away from the moon, away from Discord, and began the walk back to her throne room.
"See you soon, sister. I have not forgotten you in the dark."
Author's Note
When I got the idea for this one-shot, I immediately realized that it would have been done before (which a quick FiMfiction search confirmed), but I decided to write my take on it anyway. There's nothing new under the moon.
And now that it's done, I can go read Last Moonrise and see Tenkage's take on the same idea! My premise here might not be the most original, but that doesn't have to be a bad thing. 
Candle Wind was a very distant ancestor of Moon Dream from my other fic Dreamers and the Moon. He had a magnificent mustache and top hat.
