The Yasarian Calendar, proposed in 1656 SE by Yasar Lightfoot, is the most widely used in the world. It breaks the year (412 days) up into 9 months with an additional period at the end, known as the "Erenium", which exceptions made in 6 and 600 year cycles known as "Black Erenium" and "White Erenium" respectively. Despite these corrections, the calendar adds about one day a millennium. Several revised rules have been proposed, but none have seen official adoption by any nation.
|Month||48 days (exc. Bast)|
|Full Cycle||24 days|
|Half Cycle/Cycle||12 days|
The months of the Yasarian Calendar are:
All months are 8 weeks long (other than Bast, which is 4 weeks). Each week is 6 days, for a total of 48 days (or in Bast's case, 24 days).
Months of changing
The months Resdell, Kilam, Nadem, and Linew are months in which the seasons change, known as the "Months of Changing".
A group of four weeks is called a "full cycle", though this term is almost never used. Pairs of weeks are called "half cycles", or just "cycle". Given the length of months, cycles are more commonly used for specifying time. When using cycles, the number of the day specifies within the cycle. For instance, the 3rd of Coratt is equivalent to the 27th of Att.
The cycles of each month are Ven, Hal, Cor, and Ro. These names come from the gronoic names of the great deities: Elandra (Evendra), Paeloth (Mehalem), Ket (Cort), and Razell (Rozel). These words are treated as prefixes, e.g. the 19th day of Kilam ends Venkilam and begins Halkilam. This system is mildly irregular, and actual name for cycles varies:
As noted on the table, Bast has no third and fourth cycle, as it is only 24 days long.
Erenium occurs immediately after Bast. It is a horological black hole, not considered to be a part of any month or half cycle. It does not officially have days either, instead being a single 96-hour long period with no subdivisions, though most people will separate the day/night cycles as "days" when coordinating events or recounting stories. In most jurisdictions, Erenium isn't even "time", with the period not counting towards any contract or law specifying a duration. Legally speaking, Halbast ends, Venresdel begins, and no time passed in between.
In many cultures, the Erenium is seen as a time for new years celebration and is often met with festivals lasting the entire time.
The rules for the length of Erenium are:
Erenium is 4 days. Every 6 years, Erenium is shortened to 3 days. (Black Erenium) Every 600 years, Erenium is kept at 4 days (White Erenium)
This makes the average year 411.835 days long. This was believed to be the true length of a day at the time of the calendar's creation, but modern calculations have shown that the value to be approximately 411.8342 days. At that rate, the calendar will drift out of sync by roughly 1 minute and 26 seconds every year, gaining 1 day every millennium. Given that the calendar was adopted in 1560, it has already drifted three days out of sync, a number confirmed by historical records of astronomical events. Despite the correction in 3530, the calendar is still two days out of sync.
To account for the fractional number of days in a year, every 6 years the Erenium is shortened to 3 days. This is known as a "Black Erenium" and is often marked by indignation from those reluctant to lose a day of festivities. The previous Black Erenium occurred in 4628 and the next one will occur at the end of this year (4632).
Every 600 years, Erenium is left at 4 days. This is seen as a wonderful event. Despite Erenium only being kept at the usual length, White Ereniums have always been met with unusually grand spectacle, often bleeding over into the first week of Venresdel.
Even with Erenium, the calendar still drifts 1 day out of sync every millennium. Several fixes for this have been proposed. A common option is lengthening the gaps between White Ereniums to 1152 years. Critics of this change argue that 1152 is an awkward number compared to the existing 600. Others complain about having to wait 552 extra years for a White Erenium. As the next White Erenium is 24 years away, this is a serious point of issue for many people.
Another suggestion skipping the last day of Bast every 1000 years, in honor of the similar measure performed by King Druk in 3530.
In 3529, astronomers in Sagvelt noticed that the calendar had been drifting. King Druk I declared that in 3530, the 24th of Bast would be skipped and Erenium would begin immediately after the 23rd. King Druk requested other nations follow suit, but few listened. When the change occurred, Sagvelt's calendar became desynchronized with the rest of Niera. Slowly, to increase ease of trade with Resacorallis, other nations adopted this correction. It would take 75 years before the majority of nations had adopted the change, each by skipping the 24th of Bast.