The Celestine Calendar

The calendar here runs differently than the Gregorian Calendar.

For one, the year is 1066 AC (or Anno Celesti). The days and years are the same length as ours, but there are no months in Equestria; only seasons.

The year is broken down into four parts: Winter, Spring, Summer, and Fall. Each season has 91 days. That brings us to a total 364 days.

The 365th day is the New Year Celebration that occurs between Winter and Spring. It does not have a year, and it does not have a season. It's an all-day celebration of new things to come.

On Leap Years, Celestia has given Equestria an extra day to maintain the proper equilibrium for the seasonal changes, and those years, the New Year Celebration starts a day early and lasts for two days.

The seasonal dates correspond to the Gregorian calendar thusly:

Season Gregorian Dates
New Year Day March 21st
Spring March 22nd — June 20th
Summer June 21st — September 19th
Autumn September 20th — December 19th
Winter December 20th — March 20th
* On leap years, the New Year Celebration lasts March 20th-21st.

Holidays

The ponies have lots of annual holidays to celebrate! They celebrate things a little differently than Ponyville, though there's no reason a pony can't adopt some Ponyville traditions, or run plots similar to the events in Ponyville!

FYI, these holidays were developed prior to Season 2's release.

Holiday Celestine Dates Gregorian Dates
Winter Wrap-Up Winter 84 — 91 March 13th — 20th*
New Year Celebration New Year Day March 21st*
Day of Flowers Spring 45 May 5th
Final Rain Spring 84 — 91 June 13th — 20th
Summer Sun Celebration Summer 1 June 21st
Midsummer Bash Summer 45 August 4th
Sun's Hibernation Summer 84 — 91 September 12th — 19th
Collage of Colors Fall 1 September 20th
Ghostwalk Fall 45 November 2nd
Running of the Leaves Fall 84 December 12th
Curtain of Snow Fall 84 — 91 December 12th — 19th
Winter Moon Festival Winter 1 December 20th
Parade of Lights Winter 45 February 2nd
* On leap years, these holidays are stretched back a day on the Gregorian calendar.

The Week of Giving/Winter Wrap-Up

Winter 84-91
The last week of Winter is a combination of Winter Wrap-Up (which isn't generally too laborious, in this coastal settlement) and the Week of Giving. All week is spent giving gifts to those you love, spreading joy and delicious treats, and so on. The whole place is lit with candles at night, and the trees are decorated with popcorn and candy.

New Year Celebration

Between Winter and Spring
The Week of Giving culminates in the New Year Celebration, which is an extra-annual day that marks the beginning of a new year. It's an all-day celebration of feasting and dancing and all-out excitement. Even if the season isn't fully wrapped up, this day is always set aside for celebration. Everypony is encouraged to reflect on the events of the past year and look forward to the next year, while celebrating the present. This is why this day does not ever have a year, and when it's marked down as a date, it will always be New Year Day, 1065-1066 (or whatever two years surround it).

Every fourth year, Celestia gives Equestria another day to keep the seasons in balance. On those years, the New Year celebration starts a day early and extends into two days instead of one, and the celebration has a particularly solar bent to it.

Day of Flowers

Spring 45
This day is to celebrate Spring and all that comes with it. It's one giant birthday party for all the new foals, and there's dancing and the urging up of new spring shoots and flowers. During the day, Celestia visits all over the country to name all the new foals.
(Hey, they all get freakishly accurate names prior to acquiring a cutie-mark. This is why!)

Final Rain

Spring 84-91
Wrapping up Spring for summer! The clouds need to be kicked away, the rain abated, the harvests cleared for Summer crops… so on and so forth!

Summer Sun Celebration

Summer 1
On the longest day of the year, Celestia raises the sun. Though it takes place elsewhere, it's visible all over Equestria. It's customary for everypony to stay up the night prior to be certain to witness the sunrise, and usually parties spring up all evening to keep awake.

Midsummer Bash

Summer 45
When the heat is unbearable mid-summer, there's a big party on the beach. Swimming, dancing, water fights, and at night, enormous bonfires! Ice cream is also huge, here.

Sun's Hibernation

Summer 84-91
To wrap up Summer, the pegasus ponies bring in clouds to cover the sun and cool everything down. It rains occasionally too. The flowers are picked, the unicorns turn the leaves, the animals get help storing food for the winter… and so on. The summer crops are also picked and stored.

Collage of Colors

Fall 1
The first of fall is celebrated with an arts festival! Everyone is encouraged to be out and admire all the art, or show off their art. Doesn't matter what kind. It's also a food festival (culinary arts after all!) and everyone shares in some of the best of the last season's crops. Yum! Most of this happens in Portside along the boardwalk and the pier.

Ghostwalk

Fall 45
The Ghostwalk is mid-Fall, and ponies celebrate the lives of their lost loved-ones with what else but a party? Costumes are encouraged for ponies of all ages. There's usually a party in the town square with gifts and refreshments.

Meanwhile, foals go door to door to collect sweets and other burnable things. These are meant to be burned in the bonfire in the middle of town, as offerings to ancestors and the dead. As thanks for performing this very important deed, the foals are also given additional sweets to keep for themselves. Most of the burnable things are made specifically for being burnt, and are designed to smell good while burning, making the town square on Ghostwalk pleasantly aromatic.

Running of the Leaves

Fall 84
The marathon kicks off the wrap-up of Fall. All the ponies thundering through the race track drops the leaves from the trees in the area.

Curtain of Snow

Fall 84-91
Any remaining leaves after the Running of the Leaves are brought down. The harvests are officially collected and stores, the animals are put to bed, the birds are led off South, the clouds are brought in and darkened for snow…and so on! Prepare for Winter!

Winter Moon Festival

Winter 1
On the longest night of the year, Luna raises the moon. Everyone is encouraged to sleep all day in preparation for staying up all night to enjoy the party. Dancing, music, it's all distinctly…rave-y.

Forgettance Day

Winter 12
Long ago, Horseshoe Harbor experienced a truly, unbelievably, all-the-stars-lined-up-for-this embarrassing sort of day. Not a single pony was unaffected. Maybe it was a curse, or maybe it was just dumb luck. Either way, a wise pony suggested the whole town get drunk and forget about it.

And that is exactly what they did.

The next year, all the town could remember was how much fun they had drinking on this day, so that's what they did again. And again. And so on, and so forth, until Forgettance Day was born: fireworks, drinking, and general revelry are the hallmarks of this day, as everyone celebrates whatever-it-was this day was about. Surely something important.

Frequently, ponies will make up their own stories about what happened, but…honestly, nopony truly knows.

Parade of Lights

Winter 45
With Winter being dark and cold, the ponies like to light things up a bit. The whole town is lit with brightly colored-lights to be left up until the end of Winter. Usually, lovers give gifts to each other on this day, or to profess one's love for another. It doesn't have to be romantic love; it can also be brotherly, familial, friendly, or even just giving a gift to yourself. It is customary for pairs, then, to go and wander the streets and admire the lights, while carrying candles.