Dual Year Calendar System

The Dual Year Calendar System, otherwise known as the Mountains Land Calendar, the Long Lake Calendar, or the Tranquility-Passion Calendar, was a solar calendar used by the Long Lake / Mountains-Land civilizations. It is divided into 13 months of 28 days each, with an intercalated day at the end of the 13th month, known as Ancestor's Day. The main unique feature of the calendar was that it alternated between years of tranquility (YT) and years of passion (YP). During years of tranquility, people were meant to focus on respecting caste roles, acquiring wealth, and maintaining peace. During years of passion, people were meant to focus on love, aggressiveness, and strong spirituality.
Falsely calculating years as perfectly spanning 365 days, the calendar slowly drifted and the seasons did not match the months. By 130 YT, calendar days had shifted by about 65 days. This was corrected within the Harmony in 138 YP, and the Modified Dual Year Calendar System, as it was officially named, spread throughout the region except westwards.

Name

At its invention, the calendar was simply known as the Calendar, or Day-Tracker. Its many names originated from outside the Land at the Feet of the Great Mountains. As southern settlements began to associate the Clan of the Long Lake with the entirety of the Great-Mountains Land, the name "Long Lake Calendar" was adopted as well. The quirk of the alternating years present within the calendar fascinated all surrounding nations, who began to refer to it as the Dual Year Calendar or the Tranquility-Passion Calendar.

History

Before the Calendar

Prior to the invention of the Dual Year Calendar System, time-keeping systems were varied and in sporadic use across the Mountains Land. However, the tradition to alternate years of war and years of peace was widespread. Nearly all calendars at the time were solar, like their successor, although some may have been luni-solar. Few records of older calendars exist, however, we know that a reason for the invention of the Dual Year Calendar was the concern that some calendar dates at the time were slowly shifting in the wrong seasons.

Invention of the Dual Year System

When the Dual Year Calendar System, simply known as the Calendar (lit. the Day-Tracker) in Classical Harmonic, the date of its invention was set as the first year of tranquility (1 YT). It was created in the Clan of the Long Lake, which would become an integral province within the Harmony of the Great River, by an unknown warrior-priest, or perhaps many working together. By studying the length of days and seasons over many years, scholars wrongly deduced that the length of a year was exactly 365 days, and constructed a calendar which they thought would not drift out of sync. The year was cut up into 13 months of 28 days each, which amounted to 364 days. Thus, a day not counted in any month, known as Ancestor's Day, was added at the end of the year, bringing the number of days in a calendar year to 365. It was in use by the religious caste in order to keep of track of spiritual events and religiously important dates without them drifting out of sync with the seasons, and the intercalated day at the end of the year anchored spirituality into the lives of warrior-priests.

Widespread Adoption

The calendar was progressively adopted by the entire population of the Clan of the Long Lake and in some surrounding areas by ~10 YT (20 years after its invention), in part because few other alternatives may have existed at the time, and also due to the prestigious image the warrior-priest caste held among the general population. Intellectuals of the Clan of the Long Lake were, moreover, generally held in high regard by the rest of the Great River clans, and the Dual Year Calendar System was rapidly adopted across the river, first by religious intellectuals and traders, and then by the rest of the population. By ~40 YT, the entirety of the Mountains Land had exclusively adopted the calendar system.

Modified Dual Year Calendar System

In 138 YP, the Harmony's central government issued a recommendation to its clans to adopt the Modified Dual Year Calendar System, as the month's names (with most months being named according to seasonal features) were now inaccurate. The modified calendar added a leap day at the beginning of every fourth Germinating Month (the first month of the calendar), which came to be known as the New Year's Announcement.
This change also shifted the months so that they more closely corresponded to their own names. As not all clans immediately adopted the calendar (altho they had all adopted it within a year), many small inaccuracies in time-keeping were made during this period of change to the modified calendar.
Kindmount refused to adopt the modified calendar due to their strong rivalry with the Harmony, as well as the weak power of the government at the time, who was overwhelmed with more pressing issues.

Functioning

Notation

Years were written down as either years of passion or tranquility. Two years (one of tranquility, one of passion) were written with the same number. Thus, the number associated with the current year increased once every two years. That number therefore represents only about half of the time elapsed between the current year and year 1. For example. 40 YT denotes the 40th year of tranquility, 80 years after 1 YT, and 20 YP denotes the 20th year of passion, 41 years after 1 YT. Years before 1 YT can be written down as either a negative number or as a number B1YT (before 1 YT). Negative years follow the same rules as positive years, but years written as B1YT express the actual amount of years before 1 YT. For example, -700 YT is the same date as 1400 B1YT.
As the Modified Dual Year Calendar System was adopted in the east of the Great-Mountains Land, but not in Kindmount, the notation of these two different systems are different: YT and YP are used for the modified system, while KYT (Kindmountian Year of Tranquility) and KYP (Kindmountian Year of Passion) is used for the original non-modified system.

Division of the Calendar

Days of the Dual Year Calendar were split into 16 hours. There were 28 days in each month, which were not divided into weeks, unlike some other calendar systems. There were 13 months in a year, each with a unique name. In order for the calendar to have 365 days, a day at the end of the year was intercalated and does not belong to any month. This day was known as Ancestor's Day, and was meant as a day dedicated to honoring one's ancestors. It also acted as a transition between years of tranquility and passion, and was not considered a part of either type of year.
In the Modified Dual Year Calendar System, a leap day, known as New Year's Announcement, was added at the beginning of the first month of the year once every four years, accounting for a rotation of the Earth around the Sun being closer to 365.25 days.
The year started in early autumn, and the months were mostly named after a climate-based feature. The months were: Germinating Month, Flowering Month, Hunted Month, Harvested Month, Heated Month, Fruit-filled Month, Foggy Month, Gold-leafed Month, Month of the Birth of Cold, Dry Month, Snowy Month, Rainy Month, and Windy Month.

Related Historical Events

• 4015 HE
  Invention of the Dual Year Calendar System