Chiseian calendar

The Chiseian calendar is a which reckons years, months and days according to astronomical phenomena. It is defined by the 'Edict on the Calculation and promulgation of the Royal calendar', issued by the Royal Standards Authority of the Ministry of the Interior on June 10th, 2006. It is based on the traditional, and is used officially both in Chisei as well as in some of it's former colonies such as Masuka and Jyugoku.

Days begin and end at midnight, and months begin on the day of the new moon - they may be 29-30 days long. The Chiseian New Year begins on the second new moon after the winter solstice. Each month is divided into three 10-day weeks, known as jun (旬).

govern the addition of or leap months, which are 30 days long and added every 2-3 years, or around 7 times in a 19 year period.

Written versions historically were based on the, alongside numbering by nengō (年号 'era name'), but the former has now largely fallen out of favour outside of certain applications in historical dating, while the latter, combined with the 'dynastic year' system, has taken precedence. The year 2021 is written as Yeikō 32 or 33, while in dynastic notation it is 426 or 427.

History
The  calendar was introduced to Chisei via Hinomoto during the later migration period, around the sixth century. After that, Chisei calculated its calendar using various Hua calendar procedures, and from 1685, using Chiseian variations of the Hua procedures.

Chisei has had more than one system for designating years, including:
 * The Huaxian was introduced early from Huaxia into Chisei. It was often used together with era names. Now, though, the cycle is seldom used except around New Year.
 * The era name (元号 gengō, or 年号 nengō) system was also introduced from Huaxia, and has been in continuous use since 1100 CE. Nengō are the official means of dating years in Chisei, and virtually all government business is conducted using that system. It is also in general use in private and personal business.
 * The Dynastic Year System (王立暦 ōryūrehi, lit. "Royal Calendar"), which counts years from the foundation of the Shun dynasty in 1594.
 * The Amphian Common Era (Anno Domini) (東暦, tōrehi) system is not widely used in Chisei, but is used by multinational businesses and for dating international treaties.

Day
A day in the Chiseian calendar is defined as the period from one midnight to the next. Days are divided into ji (時), kohu (刻), hun (分) and shun (瞬).
 * Ji (Saramosiri ci) correspond to 1⁄12 of a day, or 2 hours in Amphian timekeeping. Consequently often translated as a 'Dual Hour'.
 * Kohu (Saramosiri koku) are defined as 1⁄8 of a ji, or 15 minutes. Historically they were defined as 1⁄100 of a day, or 14.4 minutes; the current definition was adopted in 1867 to align the kohu with the ji.
 * Hun (Saramosiri hon) are defined as 1⁄10 of a kohu, or 1.5 minutes. The definition of the Amphian is sometimes used instead, resulting in 15 hun within a kohu.
 * Myō (Saramosiri mowa) are defined as 1⁄100 of a hun, or 0.9 seconds. Once again, the same word is often used to refer to in Amphian timekeeping.

Week
Days are grouped into nine or ten-day weeks known as jun (旬) or, in Saramosiri, wanto (十日, lit. 10 days). Three weeks make up month. The fifth and ninth/tenth days of every week are designated as rest days, with the traditional Chiseian running from the first to fourth, and sixth to eighth days of a week.

The first week of a month is known as jōjun (上旬, upper jun), the second chūjun (中旬, middle jun) and the third gejun (下旬, lower jun). Days of the week are named from the ten.

Month
Months are defined as the time from one to the next, which averages approximately 29+17⁄32 days. There is no specified length of any particular month, so the first month could have 29 days (short month, 小月) in some years and 30 days (long month, 大月) in other years.

A 12-month-year using this system has 354 days, which would drift significantly from the. To fix this, there is a 13-month year approximately once every three years. The 13-month version has the same alternation of long and short months, but adds a 30-day leap month (閏月; ningachi), with the location of the month determined by. Years with 12 months are called common years, and 13-month years are known as long years. Long years occur every 2-3 years, or on average 7 times within a 19-year cycle.

Names of months
The first day of a month is known as tsuhitachi (月立ち, "moon beginning") or cup sapa (月頭, "month head"), while the last day of a month is known as tsugomori (晦, "darkening of the moon") or cup keseke (月終, "month end"). The 29th day of a month may be either tsugomori / cup keseke if it is the last day, or nijūku-nichi / nicuku-nici (二十九日) if second-to-last.

Solar year
The solar year (歲, sai), the time between the, is divided into 24. Each term represents a 15° portion of the. These solar terms mark seasons as well as equinoxes, solstices and other celestial events.

Pairs of solar terms are climate terms, or solar months. The first solar term is "pre-climate" (節氣 setsuki), and the second is "mid-climate" (中氣 chūki). The first month without a mid-climate is the leap, or intercalary, month. In other words, the first month that doesn't include a major solar term is the leap month. Leap months are numbered with 閏, the character for "intercalary", plus the name of the month they follow.

As the solar terms are based on observation of solstices and movements of the sun, the beginning of a solar year can vary by up to a day depending on the timezone where the calendar is calculated. Historically, this meant Hua-derived calendars in different countries, or in different parts of the Chiseian Empire, occasionally adopted intercalary months at different times, resulting in delays between calendars. Since the adoption of the modern calendar in 1846, solar terms and intercalary months have been calculated centrally under Chiseian Standard Time (EMT +0) in all territories; this eliminates delays, but does mean that in different time zones some events traditionally aligned with the winter solstice are celebrated half a day or more earlier or later than the locally observed solstice.

Solar terms have been named according to the climate of central Chisei (Eito). Consequently some terms with names derived from the old Hua calendar (based on Huaxian climate) are placed at different parts of the year, while others remain the same.

As the solar year can essentially be used as a form of, a popular method of conversion between the Chiseian lunisolar calendar and pure solar calendars is to describe a date as relative to the nearest solar term, rounded to the day, i.e 4 days before the Start of Spring, 10 days before the Winter Solstice, and so on. Multinational Chiseian businesses often structure their corporate year around the solstice.

Lunisolar year
The lunisolar year is measured from the first day of spring, defined as the second new moon following the winter solstice. This typically places the Chiseian New Year sometime between February and March in the Amphian system. Once again, as calculations are aligned with Chiseian time, there may be a few hours to a day of discrepancy with local observations based on timezone. The lunar new year is a major celebration in Chisei and the former Chiseian sphere, and the first week (10 days) of a year is a Chiseian national holiday as well as an important Jindo festival.

In the written calendar, years are typically recorded according to nengō (年号 'era names'), which are decided by the Ministry of the Royal Household following a change in monarch or to commemorate certain events. For example, the present Eikō era began on January 31 1995 CE according to the Amphian calendar. 2000 CE consequently corresponds to Yeikō 4 or Yeikō 5. New eras are often declared on the accession of a new monarch, however there are frequently multiple nengō declared throughout a single monarch's reign. For example, the reign of Grand Queen Suzumeko was broken into two nengō, the Tenhei era (天平) from 1962 - 1973, and the Man'en era (嘉永) from 1974 - 1994. It is possible for multiple monarchs to rule under a single era name. Following Suzumeko's death in 1989, her younger brother Tenkayasu succeeded to the throne, but the Man'en era continued for five more years, as its dates had been predetermined to coincide with the of the Treaty of Sumura and the  of the ruling Shun dynasty.

Until the Man'en era, eras did not have to begin on the New Year. In the event of a mid-year change in era name, the year would be recorded simultaneously under both names (e.g Tenshō 8 / Meiwa 1 or one name chosen depending on the date. From Man'en onwards, all era names have begun on the New Year.

Another popular system for numbering years, originally devised by historians, is the dynastic calendar, which counts years from the foundation of the reigning Shun dynasty in 1594. The year 2020 in dynastic notation is either 425 or 426. The dynastic notation has become increasingly popular since the late 20th century, and is today used in many contexts where there is a need for precise year reckoning and the ability to identify dates far in the future, e.g computing, apartment leases, employment contracts and publication dates.

Date conventions
Dates are typically written in the format Y/M/D, with the year given after the era name.
 * 栄光三十年三月三日
 * Yeikō Sanjūnen Sangachi Sannichi
 * Eyko Sancupa Sangaci Sannici

This means Yeikō 30 Sangachi 3, the third day of the third month of the thirtieth year of the Yeikō era (9 April 2019).

Besides Chisei, many nations which utilise the Chiseian calendar have their own conventions for reckoning years.
 * In Jyugoku and Masuka, years are reckoned based on the year of independence (from Chisei) - 1959 and 1960 respectively. A similar convention was used by the Republic of Imoshima.
 * West Kuiju, which adopted a modified Chiseian calendar in 1946, numbers years from the Unification of Kuiju in 1800.

Third Month
The first day of the third month (月立ち三日 tsuhitachi mikka) has broad significance in Chisei. It marks the beginning of the government's fiscal year. Many corporations follow suit. In addition, corporations often form or merge on that date. On this date, many new employees begin their jobs, and it is the start of many real-estate leases. It is also the first day of the Chiseian school year.

Age reckoning
In Shirakawa, Saramosir and Geusyo, ages are calculated much like elsewhere in eastern Escar, with children born at 1 years old and the age being incremented by 1 with every subsequent new year.

The character 歳 (year) is used as a counter for age.