Revision for Astronomy and Calendars - Feb. 17, 2023, 6:34 p.m.
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Threa is a planet that is roughly the size and mass of earth. It orbits a single sun, a yellow dwarf, and requires 368 days to complete one revolution, one Threan year. A single rotation around its own axis – one day – requires 24 terran hours. Unlike earth, Threa has two moons. One is slightly larger than earth’s moon, while the other is significantly smaller. Although Threa’s cultures each have their own names for the moons, the large one is henceforth referred to as Haveron and the small one as Rioath. Despite Rioath being closer to Threa than Haveron, the former still appears far less massive than the latter. Haveron is simply that much bigger.

Haveron requires exactly one Threan year to complete its moon cycle. Rioath’s takes merely a quarter of that, precisely ninety-two days. Haveron’s cycle begins – the moon is empty – when Threa is experiencing its northward equinox. Rioath is full at this moment, and again when its larger kin is 1/4, 1/2, 3/4, and fully through its cycle. Correspondingly, Rioath is empty when Haveron is 1/8, 3/8, 5/8, and 7/8 through its cycle. Whenever Haveron is full, so is Rioath. This event marks the chronological mid-point between one northward equinox and the next, the exact middle of a Threan solar year.

Additional noteworthy facts about the moons are: they are both tidally locked with Threa, they both orbit in the direction of their primary’s rotation, they move on the same plane, and Haveron is further away from Threa than Rioath. As a consequence of these circumstances, Rioath lines up with Haveron by moving in front of it three times a year: when Haveron is between the start of and 1/4 through its cycle, again when Haveron is halfway through its cycle, which marks the middle of the ongoing solar year, and one last time when Haveron is between 3/4 and all the way through its cycle. The next time the two catch up after that, another solar year has already begun.

Haveron’s and Rioath’s shared orbital plane has an inclination of a few degrees relative to Threa’s orbital plane around the sun. This means that solar and lunar eclipses do not occur every moon cycle; they are infrequent events. It is even more rare for both moons to be eclipsed simultaneously. When it comes to solar eclipses, it is impossible for both moons to partake in the same one, because whenever Haveron is between the sun and Threa, Rioath is on the exact opposite side of the planet. It is possible for Rioath to create a solar eclipse of its own, but it is far less impressive than Haveron’s because of Rioath’s diminutive size.

The moons’ cycles appear like clockwork to those that have studied them, through their precision, permanence, and how well they fit to a Threan solar year. Some astronomers wonder if this is the work of some god(s), an extremely powerful cabal of wizards, or caused by the innate magic of the planet on its own.

While this mystery will elude the more scientifically minded Threans for millennia to come, it is practical: It makes creating calendars child’s play for those who invest effort into keeping track of the moons. Rioath’s fullness basically marks the end of a season, while Haveron’s announces the exact middle of the year. Therefore calendars can easily be based on their journeys across the night sky. Leap years or similar constructs are unnecessary. The most difficult part is determining when the moons are actually full. As a consequence of their cycles’ extensive lengths, they only become slightly fuller each night. It is especially troublesome to decide whether Haveron is truly full or if it will gain a sliver more the next night. Only throughout documentation of their cycles may earn an astronomer an accurate calendar.

The presence of two moons has an influence on the tides as well. Whenever the moons are near each other, they cause a stronger than usual tide, both high and low, thanks to their combined mass tugging at the water. The mightiest tide occurs during their shared full phase, as then the sun pulls at the water as well. Many coastal animals and cultures have adapted to this yearly event. Whenever the moons are on opposite sides of the planet, the tides are somewhat weaker. Only somewhat so because Rioath’s smaller mass does not allow it to mitigate Haveron’s effect on the world’s waters much.


Based on the sun and moon cycles described above as well as on other natural phenomena, the cultures of Threa have developed various calendars, as detailed below.

This document uses the Aezkian calendar – the Rekaran calendar – to inform when an event took place. Hence, this one is the most important one to know for those who want to explore and understand Threa's history. If a historical event is important to or for a civilization that has its own calendar, then the dates are also displayed in their calendar and date format.

Aezkian Calendar (Rekaran Calendar)

Aezkian Calendar (PDF)

This calendar, which has been invented by the Aezkul astronomer Kiellan Rekara Oriak, is based on the lunar cycles. It is split into years, seasons, weeks, and days. The cycle of the large moon, Haveron, determines the length of a year. Hence an Aezkian year is 368 days long. The year is split into four equal seasons, each ninety-two days long, that are based on the cycle of the smaller moon, Rioath. The year begins when Haveron is in its new moon phase, so not at all visible, and each season's beginning is marked by Rioath being a full moon. In other words: The Rekaran calendar's seasons are identical to Threa's astronomical seasons because they each start and end either with an equinox or solstice.

The seasons are called vuniaez (waning wind), alirin (gentle breeze), variaez (waxing wind), and raekrvon (roaring gale). Their names refer to the strength of the southwesterly wind that blows across the Zephyr Plains north of the Aezrikka Zule, the aezkuls' origin. It is weakest in alirin (≙ astro. summer) and strongest in raekrvon (≙ astro. winter). Consequently, it wanes from raekrvon to alirin during vuniaez (≙ astro. spring), and waxes from alirin to raekrvon during variaez (≙ astro. fall). Owing to seasonal lag, the names are not always perfectly accurate. Despite the northward equinox having occurred, it can be a short while into spring before the roaring gale of winter begins to weaken.

Each season is split into a start day, an end day, and the eighteen weeks in between. Each week consists of five days. This partition is arbitrary. It merely serves to separate the long seasons into smaller, more manageable chunks. The start and end day of a season are a mathematical construct – deducting two from ninety-two allows cleanly dividing the remaining ninety by five. Giving a special name to the start and end of a season also makes it easier to register when a new one is about to begin or already begun. The Aezkian calendar is made to be practical and mathematically pleasing – truly the work of scholars.

The days of each week are named Dawnday, Riseday, Centday, Setday, and Duskday, in that order. Aezkian society tends to focus on working from Dawnday to Setday, using both the later half of Setday as well as Duskday to settle down and relax for the coming week, hence the names. The first day of a season is called Ava, and the last day of a season is called Liva.

Year Zero is the founding year of the first kingdom of the Aezrikka Zule. It was founded by the aezkul Serzier Ziurar Atzior, a mighty and wise aezser. The years after the founding are indicated with an "az", which stands for "After Ziurar", thus honoring Ziurar for creating the foundation of modern Aezkian society and history. Years before the founding are denoted with a "bz" hence, which simply stands for "Before Ziurar". That this refers to the hatch year of Ziurar is a common misconception among aezkul who have not yet been taught their own people’s history (or who did not pay attention in class!). Year Zero is given without an indicator, making it special compared to the years before and those after.

The Aezkian date notation is: YYY az, [Season], Xth Week, [Day] (e.g., 511 az, Vuniaez, 7th Week, Dawnday). An alternative way of writing the date is YYY az, Xth Week of [Season], [Day]. The former version is preferred as it uses the more logical order of year-season-week-day. When the referred to day is either the start or end day of a season, then the week is omitted (e.g., 511 az, Vuniaez, Ava). In colloquial, everyday use, some aezkul reverse the order, mentioning the day first and then the week and so on. An all-numeric way of notating the date exists: "YYY az|S|W|D"; YYY is the number of the year, S the number of the season, W the number of the week, and D the number of the day. This variant is usually only used for quick notes, when there is little space to write, or for stone tablets. If the referred to day is the start or end day of a season, the week number equals 0 and the day is either a 1 or a 92, respectively. The “az” can be omitted, but only if the referenced year is an az year (e.g., 511|1|7|1). A “bz” cannot be omitted.

Gren Calendar (Yggorum’s Calendar)

Gren Calendar (PDF)

The Druids of Yggorum invented the calendar of the Gren. Since the actual inventor’s identity has been lost to time and lack of a writing system, the druids claim that Yggorum Himself taught the calendar to Skog, His first druid, and therefore simply call it Yggorum’s Calendar. While the druids use the moon cycles to ensure accuracy, the calendar’s terminology and structure are based on the yearly cycle of agriculture and the passing of the meteorological seasons. Each Gren realm’s druidic circles keep track of the calendar themselves and inform the populace regularly of the current date. Without the druids’ timekeeping, the farmers would find it harder to sow their seeds at the right time, and nobles would not know when they can spare said farmers to raid their neighbors without risking the harvest.

The calendar is split into years, seasons, and eight-day-long weeks. Each year is intended to last from the end of one meteorological winter to the next. As this day slightly varies from one year to the next, the druids have decided that the first day of the year is the fourteenth day before Haveron, the large moon, reaches its new moon phase. Occasionally, some druids argue this point and try to push the date back further, especially those that live in the far north of the Gren realms, where winter lasts longer.

The word ‘year’ is non-existent in Gren vocabulary. They count their years in winters that have passed, which they refer to as Seasons of Frost. Hence the Gren say “this was five Seasons of Frost ago” or “five frosts ago” instead of “this was five years ago”. When the Gren want to state the absolute time an event occurred, they say “this event occurred XXX FF”. The abbreviation “FF” stands for “Frosts since the First” because the Gren see their Year 1 to be the first year after their primary god, Yggorum, managed to break the Eternal Frost, making at least most of the year fruitful. How many frosts ago this has been exactly is commonly argued over by the druids, but the currently most popular opinion results in the Second Frost Since the First to have happened in the year 123 bz in the Aezkian date system. It becomes more complicated when a Gren speaks of the time before the First Frost. Then they either have to refer to a time during the Eternal Frost or during the Era of Paradise. No rules for this exist, as this rarely happens outside of religious discussions or texts. More information on this topic can be found on the pages of the various Gren civilizations.

Each year has seven seasons: Season of First Seed, Season of Rising Spears, Season of Lowering Spears, Season of Harvest, Season of Second Seed, Season of Smoke, and Season of Frost.

The Season of First Seed, also called Season of Spring Seed, begins with the meteorological spring and lasts forty days, spanning the period when the seeds of spring cereals and legumes are to be sown. Gren rejoice when the druids announce it because it means the cold period is over and another winter has been survived. Hard labor and spring festivals are commonplace. Any surplus food that survived the winter is consumed.

The Seasons of Spears span the time period from the middle of spring to the middle of summer and are together 112 days long. The names originate from the fact that they are a great time for raiding and war because they lie between the planting of grain and the harvesting of the same, when the men are not required on the fields. Each of the two seasons is fifty-six days long. When the druids announce the Season of Rising Spears, then the Gren nobility knows there is plenty of time to execute military campaigns. Once the Season of Lowering Spears comes around, they know their campaigns ought to come to an end soon, so the warriors can return to their farms in time for harvesting season. If a pair of Seasons of Spears remained peaceful, the Gren colloquially refer to it as a Season of Hammers and Axes or Seasons of Labor instead because it is a prime time to build and gather wood because there is little to do on the fields and no fighting to distract them either.

The Season of Harvest lasts from late summer until early fall, covering a time span of forty-eight days. A critical time full of hard work, it requires all lowborn and enslaved men, women, and even children of a community to toil on the acres to ensure the community can survive the oncoming winter. If the matured cereals and legumes are not brought into the stores, cold and rain will destroy the plants.

The Season of Second Seed, known too by Season of Frost Seed or Season of Barley & Rye, occupies the middle of fall. It is equal in length to the Season of First Seed (forty days), and it is dedicated to the sowing of winter cereals, most famously rye and barley, which the Gren use for bread and ale respectively. Crops capable of withstanding the frost are seen as gifts of Yggorum Himself. No plant could survive the terrible, icy season brought by Yggrax, the great destroyer, without having been blessed by the divine, such is the belief of the Gren.

The Season of Smoke is a short, twenty-four days long season that revolves around preparing for  winter. Everything perishable that cannot be made to last is devoured during harvest festivals, meat is smoked, firewood stores are filled, housing is insulated, and sacrifices are burned. The acts of curing, firewood gathering, and sacrificial fires are the namesake for this season. Its announcement is a wake-up call for anyone who has not yet finished or even begun preparing.

Last and worst is the Season of Frost. It is a very long season, lasting 104 days, so from the middle of fall to the end of winter. A time of freezing temperatures, barren fields, and forests that offer little cover to hunters, it can only be survived with plenty of furs, large piles of wooden fuel, and sufficient stocks of foodstuff. Its end marks the end of the year.

Each season is split into multiple weeks and each week is eight days, so there are forty-six weeks in a year. The weeks have been established for religious reasons and to partition the seasons into smaller units of time that are more manageable, for practicality’s sake.

The eight days of a week, in order, are called: Agadiaday, Guldegday, Varhalday, Skogday, Yggorumday, Aethoilday, Svikday, Vargelfday. The days are dedicated to the most important gods and legendary figures of the Gren.

Agadia is the Gren goddess of fertility and hatching. It is seen as the birthday of the current week. Children that hatch on this day are, such is the belief of the Gren, blessed with good health. It is also seen as the best day to attempt conceiving.

Guldeg is a legendary hero, and a real one at that. He actually lived more than a hundred frosts ago. Religious texts and various pieces of his gear, nowadays artifacts, prove this. Guldeg was among the first Manhomers to start believing in Yggorum, and he spread the belief to his kin. With the help of his faith, he managed to unite the northern trezlin tribes, the Manhomers, against a terrible fire dragon that terrorized the region. Fighting as one, the newly founded Confederacy of Manhomir managed to slay the beast; Guldeg dealt the killing blow. Killing the first and only blazkul the Gren ever saw, the worst agent of Yggrax they ever faced, and uniting the Manhomers as well as making them fervent followers of Yggorum justly made him a true hero in the eyes of the druids, and all Gren peoples.

Varhal is a legendary kulslayer who supposedly led the Gren out of their underground hideouts during the Eternal Frost caused by Yggrax, slew dozens of dragons, and thus proved to Yggorum that the lin are worthy of a second chance. Slayers of beasts and kul believe this day to be the best time to start a new hunt.

Skog is the first of the druids. He is not a prophet or the first believer, because the Gren believe that the first people were created aware of their maker and worshiped him from the first second onward. Skog was simply the first lin to be blessed with the powers of trezizik; the first with whom Yggorum shared a fraction of His power. Skog then took on and taught students, who in turn taught their own students later on. Over the span of hundreds of years, this led to the creation of the various druidic circles in existence today. It is tradition for druidic mentors to test their apprentices on Skogday.

Yggorumday is dedicated to the primary god of the Gren Himself. On this day, the druids hold their usual ceremonies and rituals to honor Him. Other Gren try to, if time and resources permit, celebrate, relax, and partake in aforementioned religious events. It is an attempt at remembering the paradise that Yggorum once allowed them to live in.

Aethoil is the Gren god of agriculture and labor. That his day comes right after Yggorumday is no coincidence; it is meant to remind the Gren that they must work hard if they want to relax during the next day dedicated to Yggorum.

Svik is the Gren god of hunting and trickery. Those who worship him try to gain his blessing by completing a successful hunt on this day.

Vargelfday is dedicated to Vargelf, the divine servant of Yggorum that helps the dead find their way to the divine plane. Just how Agadiaday is the birth of the week, so is this day its death. The ancestors are honored on this day, both living and dead.

The Gren calendar has no official date notation, but Gren historians, who are nearly entirely druids, commonly use “XXX FF, Season of Y, Week X, [Day]”.

Other Calendars

Threa’s more primitive cultures and communities have created calendars of their own, but they are often inaccurate and/or based on irregular occurrences. Common examples for these are ecological phenomena (e.g., the blooming of a certain flower) and meteorological phenomena (e.g., the first ice of winter).

Said cultures rarely form large, cohesive nations and commonly live spread out across the land. This makes exchanging information and standardization harder. Consequentially, Threa’s primitive peoples have multiple, differing calendars, even among the same species or culture.

As noting every calendar that is in use by these peoples would be too difficult and time-consuming, this page instead roughly describes on a culture-per-culture basis what their calendars tend to be based and focus on.

Sozkian Calendars

The sozlin tribes primarily live on coasts and in wetlands, and many of them worship the moons as deities. Hence, their calendars are commonly based on the tides, the seasonal behavior of certain aquatic species, and the moon cycles. The ecological seasons play less of a role for the sozlin because they do not practice agriculture on a large scale. Fish is available year round and can be easily preserved by smoking it. The tribes that do consider the moons to have religious importance tend to have proper, well-documented calendars like the aezkul and Gren do. However, there is still no standardized sozlin calendar worthy of mention, because details, such as when a year starts and what a year even is, vary from region to region. Sozlin groups that live away from the coasts – usually in a swamp or similar form of wetland – and that do not worship the moons tend to base their calendars on the passing of the ecological seasons because they have a bigger impact on their food supply, given that they live off the land more than the tribes on the coast do.

Trezkian Calendars

Scattered trezlin tribes, which have not banded together to form one of the Gren realms, base their calendars on the ecological seasons and the passing of the moons. Especially the former is of great importance to them because they live mostly in the northern and central parts of the temperate zone; seasonal climate greatly affects them. It determines when hunting is best, when wild, edible plants can be harvested, and when preparations for the cold winters have to be made. For the more advanced ones, knowledge of the calendar is also important for agricultural work. As these primitive trezlin tribes live hidden in the densest of woods and have even less contact to one another than the sozlin groupings do among themselves, their calendars and means of tracking time vary greatly from tribe to tribe.

Wolshak Calendars

Wolshaks inhabit the temperate zone, the Zephyr Plains and Whispering Lowland, and the boreal zone, save for the polar regions. They live in those lands in separate packs, which are nomadic or settled, and the packs usually do not interact with each other much. These circumstances are the reason there is no proper wolshak calendar that is based on unchanging conditions. Instead, each pack has their own calendar based on the ecological seasons relevant to their habitat. An example: For the groups that live in the boreal zone, there are usually only two major seasons: a cold and a warm one. Some packs do further divide those into sub-seasons, if they have reason to do so (e.g., a certain type of fruit with spiritual relevance is only available in the earliest parts of the warm season).

Wild Kul Calendars

Whether uncivilized kul (e.g., trezkul, sozkul, mazkul, etc.) keep track of the date depends on their lifestyle. ‘Feral’ kul that live in solitary or in at most a family, such as trezkul, do not have calendars of any sort. They tend to be driven more by instinct and often do not even have a language, which makes it difficult to lay out a proper calendar to begin with. Look at trezkul, for instance: They simply sense that winter is approaching, by means of surrounding meteorological developments, and receive the urge to head to warmer areas as a result. Communal, uncivilized kul, such as sozkul, have a language and a greater degree of organization. This often results in them tracking the date for practical reasons. Their elders tend to keep an oral ‘calendar’ of sorts. They simply know that certain developments go hand in hand with beneficial or disadvantageous conditions. A good example are the moons. Most sozkul elders are aware that they have to expect especially high tides when the moons are close together. Other indicators are possible, for example: A rizkul matriarch may be aware during what sort of climate the breeding season of her group’s favorite prey begins, and so ensures her best hunters are ready at the right time.