Ashvesol Kavash (aʃ·ʋɛ·sɔl kɑ·vɑʃ)

The Seven Thousandth Sunrise

The Ashvesol Kavash is the seventh major milestone marker for any member of the Orelli royal family, and the most important celebration for the heir to the throne. Marking seven thousand sunrises since their birth, the Ashvesol Kavash is when a Dawnchild fully comes of age and becomes eligible for various adult factors of ruling: marriage, ascendance, and abdication among them. This is also when they are allowed to appoint their personal contingent of the Dawnguard.
This celebration occurs approximately one and a half months after the Dawnchild's 19th birthday on the Orelli calendar, and approximately two months after the 19th birthday on the Gregorian.

Significance

The origin of the Ashvesol Kavash comes from Where the Dawn Rests, as a part of Orela Dawnson's promise to his children. As with all Ashvesol events, it is rooted in the promise that Dawnson would grant them "A gift every thousandth sunrise." Upon his eldest child's seventh such celebration, Dawnson surprised his court by abdicating his role as King, and announcing the coronation of his child.
Since then, the condition has remained that no Dawnchild may take the throne until after their seven thousandth sunrise, requiring a regent until they come of age. The Ashvesol Kavash is also when an heir is usually confirmed, though abdications immediately upon declaration of the heir have since become rare. As the confirmed heir, rather than the heir apparent, the Dawnchild may begin to act in the name of the crown in an official capacity, allowing them much more power and freedom in the political arena.
A Dawnchild's marriage is also only possible after the Ashvesol Kavash. While an engagement can be declared at the ceremony itself, or arrangements made beforehand, the agreement is only considered binding after the sunset on the day of the Ashvesol Kavash.
The full story of Orela Dawnson's abdication includes the appointing of six guards to his child's life, one for each preceeding Ashvesol celebration. While the number of Dawnguard appointed to an adult Dawnchild now varies, the tradition of selecting their lifelong guards at this celebration continues. The ruling parent or relative may make the appointments, or the Dawnchild themself depending on personal preference. These selections are usually made with the Dawnguard Captain's recommendations.

Celebration

The Ashvesol Kavash itself, particularly those of the heir, are the most extravagant of all Orelli parties. The entire city of Dawnfall is expected to participate, with the celebrations often beginning at sunset the day prior. The Dawnchild is expected to stay awake through the night, usually kept in near-solitude in the palace temple tower while the city begins its revelry. This vigil is meant to remind the Dawnchild that every sunrise is not guaranteed, and to give them time to appreciate both The Stone Man's and the Elder Sister's blessings.
At dawn itself, all celebrants are expected to fall still until the sun has fully cleared the horizon. At that point, the Dawnchild is allowed to leave the tower, and after a change of clothes, a parade begins at the palace. Over the course of the day, the parade will wind its way through Dawnfall, with a few stops for the Dawnchild to address the crowd.
The Dawnchild's garb varies depending on current fashions and personal preferences, but an Ashvesol Kavash outfit always includes accessories of Onyx and Diamond, the two stones associated with the ruling gods of Orellia. The Onyx is for strength and insight, while the diamond represents clarity and divine blessings. A crown of the two gemstones is typical, with additions of other gemstones allowable but controversial. As for clothing, a deep blue and white ensemble is considered traditional.
As the parade ends, a ball begins at the palace. Here it is expected the Dawnchild will dance - or at least socialize - with those who will be their courtiers when they do take the throne, as a kind of preliminary exchange between political parties. If a Dawnchild has been adequately prepared, they will likely already be familiar with everyone in attendance, and know how to handle them with grace. Given the length of the celebration, it isn't unusual for a Dawnchild to disappear for an hour or two during this portion of the ceremony, both for a change of clothes and a quick nap. However, they must reappear before sunset.
At sunset, the Dawnchild is called forward to appoint their Dawnguard. They are officially recognized by their ruling relative as a full adult, and confirmed as heir if applicable. Any other gifts are bestowed on them by the crown at this point, or announcements of an abdication made. If the Dawnchild wishes, they may refute their birthright at this point in the ceremony, forfeiting any chance of inheriting the throne publicly. They will remain a Dawnchild, and still be a royal figure, but cannot ever rule themselves.
After the announcements are concluded, a ceremonial toast is given, and guests are invited to remain and celebrate until the sun rises again. Dancing, music, and other entertainment is provided across the city for the duration, and its generally expected that the crown will pay for the entirety of the celebration.

Controversy

In more recent memory, there have been suggestions about shortening the celebration, or giving the Dawnchild more time to rest. Traditionalists refute the argument, citing the role of the ceremony's length as both a demonstration of the ruling Dawnchild's strength, and a testing of the celebratory Dawnchild's endurance.
Weather is not always cooperative for a Dawnchild's Ashvsol celebrations, but storms on an Ashvesol Kavash are particularly ill omens. It isn't unheard of for celebrations to be delayed, or purposefully held at different times of year in the hopes of managing a clear sky for the relevant dawning. 
A blizzard raged during what would have been Artellia Dawnchild's Ashvesol Kavash - many attribute that as a sign of the Theoli revolution, which began the following year.

Etymology: 
Ashwe - 'to rise'
Sol - 'suns'
Ka - 'seven'
Va - 'ten'
Sh - 'zero'