Usually she'd put comparatively little stock in millennium-old legends, but this is a primary source, and the authors made some correct predictions on other matters, and the translator is good, and she double-checked to make sure the page numbers matched up so no one has been pranking her with inserted extra leaves. And the prediction is fairly dire.
And it's rather short notice.
Clarity tucks the book into a saddlebag and trots up to the main section of the palace. She can usually get an audience fairly quickly; Celestia has taken a particular interest in her since her admission to the School for Gifted Unicorns. This day is no exception. In fact, the guards usher her in even quicker than she'd usually expect.
"Princess, I have something urgent to tell you," Clarity says, mid-bow.
"Oh? What is it, Clarity?" inquires Celestia.
"I've found a prediction stating that on the longest day of the thousandth year -"
"Clarity," sighs Celestia.
Clarity grits her teeth; she's never told Celestia not to interrupt her. You can't tell the princess that. "Yes, Princess?"
"I have the utmost respect for your diligence at your studies, but you've got to take your nose out of those dusty old books now and again," says Celestia with a warm half-chuckle. "There's more to a young pony's life than studying. You're in the prime of your life, you're coming up on the end of what you can learn from school -"
Clarity stands up on all fours, no longer bowing, jaw slightly open.
"And," continues the Princess, "you need to make some friends. I worry about you all alone, you know. Weren't you invited to that party - who was it, Moondancer?"
"Yes, I was invited, but I barely know her," says Clarity.
"Perhaps the ponies around Canterlot just aren't clicking with you. You know what," says Celestia, as though seized with sudden inspiration. "I'm going to give you a job to do."
"...a job, Princess? But what about the longest day of the thousandth -"
"Clarity," says Celestia again, and Clarity shuts her mouth. "Don't you worry about it. I'm sending you to supervise the preparations for the Summer Sun Celebration. It's being held in Ponyville this year. I'll arrange a carriage for you. Pack your things, you leave in two hours."
"I..." Clarity can't really gainsay her. "Yes, Princess."
Celestia smiles.
Clarity bows again, and leaves, and packs.
-
She's in the air, drawn with her luggage in her carriage by someone in good condition for a long-distance flight - they're still working on that train line.
She steps onto the main street of Ponyville, laden with all her possessions in her saddlebags, and levitates her to-do list in front of her nose.
"Okay," she sighs to herself, peering at the first item. Clarity is pretty sure Celestia has read every book in the palace library at least once; probably she investigated the danger well in advance and dismissed it. (But Clarity will be staying in a library while she's in Ponyville, so she'll have a chance to double-check and find corroborations once she checks out the Summer Sun Celebration preparations.)
"First," Clarity mutters, "banquet preparations. Cheery Cherry Orchard."
And off she trots, following Silver Streak's directions to her sister's place to issue a reminder about clearing the sky.
Just as Streak promised, there is a tower on the far side of town, some distance down the road from the main cluster of buildings and set a little ways back from the street. As Clarity approaches, mysterious sounds emerge: clanging, clinking, and a crackling whoosh almost like a strong wind.
"Just a miiiinute!" calls a voice that is similar to Streak's, but used very differently. In four syllables, this pony has varied her tone more than Streak did in her and Clarity's entire conversation.
"Hi!" she says cheerfully. "What's up?"
"Hi, you must be Brightblaze. I'm Clarity Bell, and the Princess sent me here to oversee the preparations for the Summer Sun Celebration -"
"Oh gee, that's today?" she says. "That's totally today, isn't it."
"Well, it's technically very early in the morning tomorrow, but the sky should be cleared, and you're on my list as responsible for that."
And she disappears back into the tower. A moment later, the clanging resumes.
Clarity isn't sure whether that was intended to be the end of the conversation or not, so she stays put for another minute in case Brightblaze is going to come back of her own accord.
It takes about ten seconds to get them all. Then Blaze arcs down toward the front of the tower, brakes by pointing her hooves at the ground, turns off the boots, and lands beside Clarity in normal pegasus fashion.
"What'd I tell you?" she says, grinning.
"That's 'cause I made 'em!" she says, tossing her head. "That's what I do. I make things. Cool things that do stuff. Runs in the family - my dad's been trying to invent self-propelled flying carriages since he was my age."
"Huh. That would be pretty cool if he pulls it off," says Clarity. "Are the boots magic?"
Blaze giggles. "That's okay. Anyway, nice meeting you! Have you checked on everypony else? My sister and Cordy are doing the food and music; I can't remember who else is doing what..."
"It's everypony on my list, anyway, and I'm supposed to be staying at the library until after the celebration, at which time I'll go home."
"That sounds kinda boring. Unless you really like books, I guess. Do you really like books?"