Twilight Sparkle stood across the Canterlot Meridian, with her left hooves in the western hemisphere of Equestria, and her right hooves in the east. The tip of her horn and the pink streak of her tail perfectly aligned with zero degrees longitude. She looked up at the clock tower of the Abbey of the Time Turners in front of her, lost in thought.
It was said that there were worlds where the movement of the heavens was set by the laws of physics. Where planets would circle around stars, spinning such that each side experienced alternately day, then night. Moons would cycle through monthly phases set by their orbital motion. Any creatures on such a world, Twilight speculated, would recognise patterns in the movements of lights in the sky, and thus learn to tell the time and decipher the laws of nature. It must be fun to study astronomy in such a world.
But here in the magical land of Equestria, the movement of the heavens was controlled by magical beings. The stars were kicked about in games of hoofball by the ursas. The planets would wander across the sky to visit friends. The sun and moon had to be coaxed above the horizon by alicorn princesses, and gently directed back to bed when the day or night was done. This made the business of telling the time a bit more complicated, and even more important.
The abbey was a group of ancient stone buildings built around a plaza on a ledge in the cliff high above Canterlot. Here, a stream flowed out of the rock—fed by whatever magic it was that brought fresh water to the surface hundreds of miles from the ocean. The water cascaded down into the abbey compound, where it was collected in a large cuboid cistern, and then fed through a complicated mechanism into a narrow precision cut channel. This ran across the plaza, between Twilight’s legs, then through a grating in the wall, where it cascaded further down the cliff to Canterlot and beyond.
She had always loved visiting the abbey, ever since Princess Celestia had first brought her here as a young student, and explained to her about the principle of keeping time. And this visit would be especially fun as she was sharing it with her young friends who loved learning new things. She turned around and walked across the plaza to a stone parapet where the Cutie Mark Crusaders were admiring the view.
“Wow,” cried Scootaloo, with her fore-hooves placed on the stone wall staring over the cliff edge and flapping her small wings in excitement. “This is awesome. You can see the entire world—there's Cloudsdale, and Ponyville, and the Everfree forest.”
“You can see the old castle in the middle of the forest,” said Sweetie Belle.
“I think I can make out Sweet Apple Acres—that’s our barn,” said Apple Bloom. “And there’s the river. And that must be the scariest cave in Equestria.” She pointed her hoof over the landscape. “And there's the valley where we tried to get our cutie marks in zip-lining.”
Twilight Sparkle smiled and let them admire the panorama. Once they had fallen silent, she said, “When you're ready, there's something I want to show you. This place is the home of a very special group of ponies, and some personal heroes of mine: The Order of the Time Turners.”
“Order of the time turnips?” said Apple Bloom. “What d’they do?”
“They keep time. They keep track of every second which passes. And they publish an excellent range of calendars and diaries, including my favourite week-to-two-pages personal organiser.”
“Keep—time?” Apple Bloom pulled a face. This was not a concept that the Apple family were familiar with, being more used to keeping apples, pigs, sheep, and track of the weather schedule and fruit price index.
“You mean, they like have a stopwatch, and they time how fast Rainbow Dash can fly?” cried Scootaloo.
“It's much more than that,” said Twilight. “They keep track of time itself.”
She looked at the faces of three thoroughly puzzled little ponies.
“How do you tell the time?” she asked them.
“Ooo, ooo,” replied Sweetie Belle, “I know! You look at the clock face, and the little hand shows what hour it is, and the big hand shows how much past the hour it is, and...”
“But what do you do if your clock has stopped?”
“You wind it up and set it to the correct time,” said Apple Bloom.
“But how do you know the correct time?”
“Well... You find another clock. Or go and look at the Ponyville clock tower.”
Twilight smiled. They were starting to get it. “But suppose the Ponyville clock tower clock stops. How do we know what time to set it to?”
There was a pause while the crusaders pondered this problem. Then Sweetie Belle's face lit up.
“You can use a sundial!” she cried. “It always gives the right time, as Celestia raises the sun at the same time each day!”
“Well not quite the same time every day,” said Twilight. “She has to raise it earlier in the summer, than in the winter. But you're right, we can use Celestia's sun to tell the time, as every day, it's at its highest point at noon.”
Sweetie Belle beamed with the satisfaction of having got it right.
“But,” said Twilight, moving on to the next stage of the tutorial, “that’s only because Celestia puts it there. How does she know when to raise the sun?”
“She must have her own clock,” cried Apple Bloom.
“Yes,” added Scootaloo. “She must have a super fancy pony princess watch. Bet it's digital!”
“And what does Celestia use to set her watch?”
“The sun of course!” said Scootaloo.
“No silly,” said Apple Bloom. “She can't set her watch by the sun, because she sets the sun by her watch.”
“That’s right,” said Twilight with a satisfied grin.
“So she must use the clock tower,” continued Apple Bloom. Twilight stopped grinning.
“I'm not sure that works,” said Sweetie Belle.
“Yes it does,” insisted Apple Bloom. “Celestia sets her watch by the Ponyville clock tower. Then she raises the sun according to the time on her watch. And the clock tower keeper sets the clock when Celestia's sun is at noon. It all makes sense!” She traced out a circle in the air in front of her with a hoof to illustrate the line of her reasoning. Then gave a puzzled look as if she didn't entirely believe it.
Twilight explained: “If we want to set the time on any clock, we need another clock to do it. Celestia needs a standard clock to tell her when to raise the sun. We can only tell the time as accurately as the best clock we have.”
“Can’t you tell the time by magic?” asked Sweetie Belle.
“Not very well,” said Twilight. “Magical clocks are notoriously unreliable. Anything magic has a tendency to take on a life of its own. They get bored of running at the correct speed, and decide to run slower or faster, and sometimes play pranks on unsuspecting ponies. We need a super-regular, one hundred percent reliable, non-magical clock to keep proper time. Running that clock is a very important task. It's the duty of the ponies of the Order of the Time Turners.”
As she was talking, a familiar earth pony stallion, wearing a collar and tie, with an hour glass cutie mark walked up to join them.
“You remember Doctor Hooves from Ponyville?” said Twilight.
“Sure. Hello Doctor,” said Apple Bloom. “Do you need any apples?”
“The Doctor is a member of the Order,” said Twilight. “He has agreed to give us a tour of the abbey.”
“Hello,” said the Doctor. “Hello Apple Bloom. Hello Sweetie Belle. Hello Scootaloo. And hello Princess Twilight Sparkle. Come on, come on. There's lots to see and we haven't much time if we're to see everything in the abbey and learn all about the history of the Order, stop for tea, and get through everything before dinner. Let's start over here.” Beckoning them with a hoof, he trotted across the plaza. The four ponies followed him over to a curious contraption built just below the large water cistern fed by the spring.
“Behold the Equestrian Universal Absolute Time Standard Mark One.”
A steady flow of water was trickling out the tank. This flowed along a short chute, and then into a large metal bucket connected to one arm of a large balance. The other end being terminated with a metal counterweight. The balance see-sawed on a pivot. For a while it was resting with the water bucket high in the air, but as they were watching, the bucket filled with water. Once full, its weight tipped the balance over, sending the counterweight into the air, and the water bucket downward, until it was tipped over and emptied its contents into a stone basin on the ground. It then swung back upwards, and the counterweight fell back down. The movement of the counterweight pushed a lever, which in turn pushed a circle of pegs on a wheel driving a clock mechanism. As the see-saw fell, it moved the wheel around by one ratchet, and the long hand on a small clock face, mounted to one side, advanced by six degrees. Looking upwards, they saw that it matched the time shown by the large clock at the top of the tower.
“Wow! This is great—what is it?” cried Scootaloo.
“It is The Minute,” replied the Doctor. “An ancient water clock, so-called because it counts the time of one minute. We have a steady flow of water out of the cistern. Every sixty seconds, the bucket fills with water and its weight tips the lever arm, and the clock hand moves forward one sixtieth of the hour. A basic, but functional timepiece. It was built nearly two thousand years ago by ponies searching for a way to regulate time which didn't require them to keep turning hour-glasses. A simple water wheel wouldn’t do as it would turn at a different rate depending on the flow of the stream, but here, the water flows from the stone cistern, fed by the stream and kept full, so with a constant head of water, the rate at which the water flows into the bucket is steady and is used to set the clock. For hundreds of years, this was the clock which kept Equestria running to time, telling Celestia when to raise the sun, Luna when to raise the moon, and everypony else when it was time for lunch, dinner and supper. These days, of course, we just run it for fun—and for its heritage value. But in the olden days, Luna and Celestia would fly up here to the abbey twice a day to make sure they raised and lowered the moon and sun at the correct time.”
“Why don't you use it anymore?” asked Apple Bloom.
“It's not nearly accurate enough. It can gain or lose many minutes a day.”
“Does that really matter?” asked Sweetie Belle.
This was not a good thing to say to a member of the Order of the Time Turners. The Doctor gave Sweetie Belle a stern look. “It matters very much indeed. If we cannot keep accurate time, Celestia and Luna would raise and lower the sun and moon at the wrong time.”
“What's the problem?” asked Scootaloo. “So what if Celestia's a few minutes late raising the sun? Then we just get a few minutes extra in bed.”
“That would have very serious consequences. As was discovered by the ponies of this Order many hundreds of years ago. Now that is an interesting tale, and it includes the story of how a young filly got her cutie mark. Would you like to hear it?”
“A cutie mark story! Yes!” answered the three fillies in unison. They sat down on the ground and looked up at the Doctor expectantly. The stallion assumed the pose of a story-teller, with a sly smile and a twinkle in his eye. He opened a book he had left lying on the ground with a hoof.
“It’s all explained in this journal. It all began on a cold winter day.”