The Yamataian Calendar is the standard calendar system used in and around the Yamatai Star Empire. It is also used by the Democratic Imperium of Nepleslia, which adopted the calendar while it was a part of Yamatai, and by the Elysian Celestial Empire for external affairs (internally, it uses the Elysian Calendar).

On the Star Army wiki, years are managed with the Years Schema.

Prior to YE 39 (OOC: 2017), many in Yamatai and Nepleslia also used a 12-month, 365-day “operational calendar” that was introduced by the Nerimian Defense Initiative, an allied military, when the Grand Star Army was still being formed. In YE 39 this practice was dropped, and it is no longer standard in the Star Army of Yamatai and Yamatai Star Empire.

At first, Yamataigo (邪馬台語) characters were used to mark dates. Starting in YE 43, the use of decimal-style notation became common because of its ease of use, and language neutrality. A major factor was the Star Army's adoption of the decimal format as standard, which quickly spread to other parts of Yamatai and the Kikyo Sector.

For history in general, see Timeline.

Dates are written as YE YY.M.DD; for example, YE 44.9.35 for the 35th day of the 9th month of YE 44.

Dates prior to YE 01 are written as BYE 01 (the year before YE 01), and so on. The years are reversed but the month and date are used in the same way as YE years (e.g. BYE 05.1.1 is the first day of BYE 05).

Yamataian calendar dates were traditionally written by Yamataians in the format: 25日 8月 YE 39 (DD M YY). It is also fine to substitute M for 月 and D for 日. This became less widespread by YE 44 because the decimal system is easier to type.

Nepleslians sometimes used a traditional¹⁾ M/DD/YY format, for example 9/35/44, although this has become rare as of YE 44 when the decimal-style notation became the standard.

The years of the Yamataian calendar are preceded by the notation “YE” which is short for “Year of the Empire” and/or “Yamatai era.” YE 01 is the first year of the Empire, YE 02 is the second year of the empire, and so forth. The YE is followed by one space, and then the number (YE 04, not YE-04 or YE04). The first 9 years are typically written with two digits (YE 03, not YE 3). The Yamataigo symbol for year is 年 (nen), used as in “22年.”

The years contain 315 days, based on the rotations of the Yamatai (Planet) around its star.

The suffix -nendai (年代) is used as a counter for decades. For example, 20年代 is the twenties (YE 20-YE 29).

Age is expressed in a straightforward count in years. It is common for people to use their original or cumulative age, not the age of their bodies, if they transfer their consciousness into a new body. To express someone's age in years, Yamataians may use the counter 歳 (sai). For example, the page of someone who is 20 years old would be written as 20歳. Note that Yamataian years are shorter than Earth years. There is a conversion chart later in this article.

The Yamataian year is divided into 9 months, each consisting of 35 days.

Months are most commonly written in arabic numbers followed by the “month” kanji 月 (gatsu), e.g 7月. In Trade this is usually written as 7/01 (for the first day of the seventh month), etc.

Month	Name	Notable Events
1月	一月 (ichigatsu)	👘 Coming of Age Day
2月	二月 (nigatsu)	💖 Love Day
3月	三月 (sangatsu)	🌸 Hanami, Hinamatsuri
4月	四月 (shigatsu)	🎏 Children's Day
5月	五月 (gogatsu)	Kikyō No Sekku
6月	六月 (rokugatsu)
7月	七月 (shichigatsu)	👵 Keiro No Hi 🌊 Ocean Day
8月	八月 (hachigatsu)	🍬 Candy Festival (17日) 📜 Constitution Day (35日)
9月	九月 (kugatsu)	🎄 Year-End Traditions

There are 315 days in each year on the Yamataian Calendar and 35 in each month. There are 24 hours in each day. The Yamataigo (邪馬台語) kanji for day is 日. For example, 35日 means “Day 35” or “The 35th Day.”

There are 7 days of the week and 5 weeks in every month. Yamataians consider Moon Day the first day of the week. The first day of the month (and year) is always a Moon Day and the last day of the year and month is always a Sun Day.

This section has the Yamataigo name for each day of the month and what day of the week it falls on.

Time is expressed in hours. Each standard day has 24 hours in it. Traditionally there are 60 minutes in an hour, and time is expressed in a 24-hour clock. For example, 20:15 for a quarter past 8 p.m.

Starship personnel often use decimal fractions instead of minutes. For example: 21.50 for half past nine p.m.

Yamatai does not have time zones or daylight savings time. Time is aligned with Kyoto so early on the clock is also early in Kyoto.

Many inhabited planets also have their own local time systems.

This section deals with how to convert Yamataian time into other calendars.

Four Yamataian calendar years are equal to one Abwehran year.

Years of the Elysian Calendar line up with Yamataian years almost evenly. Elysian years are typically written using roman numerals, but are listed here in arabic numerals for convenience.

Years of the Poku Saeruo Degonjo line up with Yamataian years almost evenly. See Kyn'ka (History). Note clan years would actually be in Octal, but are listed here in decimal on the table for convenience.

The orbital period of Maekardan is 474 days long, and approximately 33% longer than that of Yamatai, meaning that there are 3 AR every 4 YE; therefore, the years of the Iromakuanhe Calendar increment by .75 for each Yamataian year. The start of YE 39 lines up with the start of AR 942 on the Iromakuanhe Calendar.

Although the Earth is not in the Kagami Galaxy where the RP takes place, it may be useful for OOC purposes to compare 365-day Earth years to 315-day Yamataian years.

Wes created this article on 2016/10/26. Authored and approved by Wes on November 9, 2016²⁾

It's taken us forever to detail the in-character months but I've done it, finally. I had to go with 9 months because it was the only way to divide 315 days (the canonical year of planet Yamatai) into “normal” size months and get whole numbers. Interestingly, this means if you've been using Earth years for your character's age instead of Yamataian years, your character may be younger than you thought they were! If you have a problem with that, feel free to resubmit the character with the “corrected” age.