This article was originally posted to Freelance Traveller’s website in 2002 and reprinted in the December 2013 issue.

Calendars are a major part of our lives, and have been for millennia. For the most part, they began with agricultural societies, and crude observations of stars, seasons, and tides. From there, they progressed to more refined observations, and often took on religious significance as well. Further refinement and social progress led to use of calendars for advance planning, and fiscal accounting—but the calendar is always there.

In spite of the large number of cultures that developed independently on Terra, there has been a remarkable similarity among the calendars, with the same numbers appearing time and again. Many of these numbers are tied to natural rhythms or other Terran phenomena; others have mystical significance due to mathematical properties. But what if you’re not starting on Terra?

This article looks at other calendars. We don’t try to analyze the reasons behind them, only to give the rules governing the count of days in them. It is up to the referee, or background author, to develop the history of the calendars and of the societies.

It is necessary to define some terms that will be used in the rest of the article, to reduce confusion. The term ‘day’ is reserved for the standard Imperial day of 24 hours; a local planetary rotational cycle, regardless of length, will be referred to as a ‘sol’. Similarly, the term ‘year’ is reserved for the standard Imperial year of 365 days; a local planetary revolutional cycle will be referred to as an ‘anno’.

All of the information here is derived from published material generally held to be canonical, from GDW and DGP, during the Classic Traveller and MegaTraveller eras.

### Imperial Calendar

The first calendar we will look at is the Imperial calendar itself: this calendar is based on a year of 365 days. Each day is subdivided into 24 hours, each of which is divided into 60 minutes, and each of those is divided into 60 seconds. The days are numbered sequentially from 1 to 365. There is a semi-formal subdivision called a ‘week’, consisting of seven days; the days are named Oneday, Twoday, Threeday, Fourday, Fiveday, Sixday, and Sevenday; these are normally elided into Wonday, Tuday, Thriday, Forday, Fiday, Sixday, and Senday. There are exactly 52 ‘weeks’ in a year; day 001 is not part of any week, and is traditionally a holiday, called “Holiday”. Day 002 of any year always falls on the first Oneday. Dates are normally written in the form ‘001-1105’; the number before the hyphen is the day number; the number after is the year number. 001-0000 is the date of the founding of the Third Imperium by Cleon Zhunastu, and corresponds to the Gregorian calendar date January 1, 4521.

### Vilani Calendar

There has been some confusion about the structure of the Vilani calendar; two different lengths for both the sol and the anno have been given by different sources. When information given about Vland is checked against the formulæ given in World Builder’s Handbook, it is found that the ‘best fit’ is for a sol of 32 hours, and an anno of 500 sols. The sol is divided into four quarters, or ten tenths; each tenth is further divided into 100 mils. Traditionally, the Vilani count the dawn-to-dusk period (dran) separate from the dusk-to-dawn period (dir). Thus, there are 1000 half-sols (drandir) in a Vilani anno. The anno is considered to start at dawn; this is drandir 000 of the year; at dusk, drandir 000 ends, and drandir 001 begins. Dates are written in the form ‘3882.001’; the anno number is before the decimal point; the number of the half-sol is after. There are two correspondences given; both cannot be correct: either Imperial year −4045 is Vilani anno 1, or Imperial year 1120 is Vilani anno 3882. Vilani anno 1 is the date of founding of the Vilani Grand Empire of the Stars (Ziru Sirka). An exact match between specific dates on the Imperial and Vilani calendars has not been given; for simplicity, assume that the beginning of the corresponding year (whichever one is chosen) matches on both calendars.

### Solomani Calendar

The Solomani dating system is a close match in terms of sol and anno lengths to the Imperial and Sylean systems. The sol is equivalent to the day, and divided similarly; the anno is generally 365 sols. However, the Solomani calendar is still closely tied to astronomical phenomena on Terra, and, as the Terran anno is not exactly 365 Terran sols, some adjustment to the calendar is needed. There is a complex rule that adds an extra (intercalary) sol to the calendar in 97 out of every 400 annos. The anno is divided into 12 ‘months’ of varying but roughly equal lengths; each month has a name and a fixed number of sols. The month names, in order from the beginning of the year, and the number of sols in each, are: January (31), February (28), March (31), April (30), May (31), June (30), July (31), August (31), September (30), October (31), November (30), December (31). The extra sol, when needed, is added to February. Sols are counted sequentially from 1 in each month. There are several common forms for writing dates, some of which are potentially ambiguous. The two most common unambiguous forms are ‘January 1, 5641’ and ‘1 Jan 5641’; the year is the last number, and the month name may be abbreviated to its first three letters. 1 Jan 0001 is held to be the traditional date for the religious initiation of a significant religious figure on Terra. The Solomani date 1 Jan 4521 corresponds with the Imperial date 001-0000.

### Zhodani Calendar

Less is known of the Zhodani calendar than of others. The Zhodani sol is 27.02 hours in length, but how it is subdivided is unknown. The anno is 244.44 sols in length. The anno is divided into six named ‘seasons’, each of 40 sols. Within a season, sols are both named and numbered, although the names are not generally used. There are also four sols that are not part of any season, and are individually named. Each group of three annos is called (in translation) an ‘olympiad’; the third anno of each olympiad has an intercalary sol added, and the third anno of each third olympiad has an additional intercalary sol added. The translated names of the seasons and extraseasonal sols, in order from the beginning of the anno, are Sunbright (sol), Rain, Moon Day (sol), Heat, Sunflight (sol), Waning, Harvest, Thanksgiving (sol), Chill, Olympiad Day (intercalary sol), Double Olympiad day (second intercalary sol), Thaw. Dates are generally written ‘3471.1 Rain 1’; the number before the point is the olympiad number, the number following the point is the year number within the olympiad, the name of the season or extraseasonal sol follows, then, at the end, the number of the sol within the season (omitted following an extraseasonal sol). It is known that 3471.1 Sunbright corresponds to Imperial date 289-1112. 1.1 Sunbright is simply the date that the olympiad system of dating was instituted.

### Aslan Calendar

The Aslan calendar is based on a sol of 36 hours and an anno of 212.2 sols. The sol is divided into 16 parts, each of which is further divided into 8 parts, each of which is further divided into 64 parts, each of which is divided into 8 parts. The anno adds an intercalary sol every fifth anno. Each sol is named, but for simplicity in dealing with extra-Hierate operations, number the sols from 1 at the start of each anno. No standard format for writing dates is known; it is generally accepted to write the dates following the Imperial format, but with the letter 'A' or the word ‘Aslan’ following. 001-0001A is held to be the date on which the Aslan Council of Twenty-Nine convened for the first time. Aslan anno 3644 is held to correspond to Imperial year 1111, but no exact date correspondence is given.

### K’kree Calendar

The K’kree sol is 28.6 hours long, with 368 sols in an anno. The sol is divided into four ‘watches’ or ten parts, each of which is further divided into tenths, hundredths, and thousandths. The anno is divided into ten parts of 37 sols each; the fourth part contains only 35 sols. Part-annos are numbered from 1. Sols are numbered within a part starting with 1. No exact match of Imperial and K’kree dates is given; it is generally held that K’kree anno 7713 corresponds to Imperial year 1110. The K’kree have not objected to the common Imperial practice of writing the date as ‘7713.5 23’; the number of the anno is placed before the point, the specific tenth-part of the anno is placed after, and then the number of the sol within the part is given. Note that as tenth-parts of the anno are numbered from 1, 7713.1 1 is not the same as 7713.10 1.

### Hiver Calendar

The Hive Federation calendar is based on a 30 hour sol, subdivided into 6 intervals. There are 143 sols in an anno, numbered from 1. Dates are written ‘1401/001’ with the anno number before a slash and the sol number after. 0001/001 is the date of the selection of Glea as the administrative center of the Hive Federation. Hiver anno 1401 corresponds to Imperial year 1111, with no exact match given.