The Chronicles of Local Space

A fictional exploration of nearby star systems

Calendars

The various colonies in Local Space mostly use local calendars to track the years and seasons of the various worlds. The calendars of Earth are also used in contexts where they are important, such as interstellar commerce, with the Standard Calendar of Earth being particularly important. Some worlds also use the Standard Calendar of Earth as the standard calendar. This generally occurs on tidelocked planets without a natural day-night cycle.

World	Calendar	Average Length of Calendar Year			Notes
World	Calendar	Local Days (exact)	Local Days (decimal)	Standard Days (decimal)	Notes
Earth	Standard Calendar of Earth	365¹⁵⁹⁄₆₅₆	365.242378	365.242378
Lysander¹					¹Artificial day (tidelocked world).
Calena²					²Artificial day (tidelocked world).
Bessel³					³Artificial day (space settlement).
Hydra Base⁴					⁴Artificial day (space settlement).
Lagrangian space settlements⁵					⁵Artificial day (space settlement).
Lunar settlements⁶					⁶Artificial day (slow-rotating world).
Sabrina⁷					⁷Artificial day (slow-rotating world).
Serenese Federation⁸					⁸Artificial day (tidelocked world).
Techbase⁹					⁹Artificial day (space settlement).
Aridia	Aridian Fixed Calendar	336	336	389.515335
Binaria Major	Binarian Calendar	224³⁵⁄₃₃₃	224.105105	266.025405
Humus	Researchers’ Calendar	404⁵⁄₇	404.714286	379.086904
	Abrahamic Calendar	404⁸⁷⁄₁₂₂	404.713115	379.085807
	Common Calendar	404⁸⁷⁄₁₂₂	404.713115	379.085807
Lacandia	Lacandian Settlement Calendar	281⁶¹⁄₈₇	281.701149	269.128813
Lacandia	Lacandian Perpetual Calendar	281⁶¹⁄₈₇	281.701149	269.128813
Mareenia	Mareenian Calendar	341²⁸⁄₄₁	341.682927	327.904641
Mars	Martian Calendar	668⁴⁵⁄₇₆	668.592105	686.972539
Prometheus¹⁰	Promethean Calendar	360	360	360	¹⁰Artificial day (tidelocked world).
Shandiana	Shandiani Calendar	184⁵⁷⁄₁₀₀	184.570000	192.967875

Intercalary Years

By interplanetary agreement, most calendars that perform arithmetic-based intercalation use the same algorithm to compute the timing of the intercalary years. Intercalary years are commonly called leap years, but may have other names in some cultures and on some worlds.

Given:

Cycle (C) is the number of years in the leap year cycle.
Delta (Δ) is an integer such that the expression ^Δ⁄_C closely approximates the length of the fractional part of the year.
Epsilon (ε) is a correctional or offset value that is a positive number less than the Cycle length, which is used to control when leap years occur.
Remainder (R) is the remainder of the division, or modulus.

Determine leap years as follows:

(Year × Δ + ε) mod C = R
If R < Δ then the year is an intercalary year with extra days.

Gregorian-style leap year rules have flaws that caused them to be rejected as the interstellar standard. They are difficult to adopt generally, have a rather large error range, and are rather complex, often requiring three or four levels of nested rules just to get four digits of precision. Such convoluted rules are similar to the epicycles, equants and deferents of Ptolemian astronomy and were eschewed because the simpler rule shown above achieves higher precision with a single rule.

Intercalary anniversaries

Calendars with intercalation also have a single interstellar standard for observing anniversaries of events that occurred on the intercalary days. Intercalary days usually fall at the end of a month, so are treated as the last day in that month for anniversary purposes. The last day in the equivalent month in years that lack an intercalary day becomes the anniversary day. In the Gregorian calendar, this method would make February 28 in common years the anniversary day for February 29 in leap years, both dates being the last day in February.

Some calendars have intercalary weeks instead of single intercalary days, such as the Martian Calendar and the Mareenian Calendar. Anniversaries in these calendars work similarly except the day of the week must be taken into account as well.

Anniversaries of events that occurred in the last week of long years (Martian Calendar)
	Week	Mo	Tu	We	Th	Fr	Sa	Su
Last week of long years	96	22	23	24	25	26	27	28
maps to		↓	↓	↓	↓	↓	↓	↓
Last week of short years	95	15	16	17	18	19	20	21

Anniversaries of events that occurred in the last week of long years (Mareenian Calendar)
	Week	Mo	Tu	We	Th	Fr	Sa	Su
Last week of leap years	49	29	30	31	32	33	34	35
maps to		↓	↓	↓	↓	↓	↓	↓
Last week of plain years	48	22	23	24	25	26	27	28

Jurisdictions with leap-week calendars generally do not skip weeks for fiscal purposes such as the calculation of interest on debts. For example, the calendar of Mareenia has a 4-week cycle to facilitate the handling of these kinds of recurring fiscal obligations.

Length of the Week

The majority of settled worlds use a calendar with a seven-day week. Generally, worlds that employ a seven-day week also have calendars that observe the strict progression of weekdays with no skipped days and no epagomenal days. This is due to the influence of members of the Abrahamic religions such as Judaism, Christianity and Islam, for whom an uninterrupted weekday cycle is mandated by their beliefs.

Remember the sabbath day, to keep it holy. Six days shalt thou labour, and do all thy work: But the seventh day is the sabbath of the Lord thy God: in it thou shalt not do any work, thou, nor thy son, nor thy daughter, thy manservant, nor thy maidservant, nor thy cattle, nor thy stranger that is within thy gates: For in six days the Lord made heaven and earth, the sea, and all that in them is, and rested the seventh day: wherefore the Lord blessed the sabbath day, and hallowed it.

The Bible (King James version), Exodus 20:8–11 (Fourth Commandment)

The uninterrupted seven-day week is not mandated by interstellar agreement but is recommended as a default length of the week if no compelling reason exists to employ a week of a different length. Individual worlds are free to use a week of a different length should they choose to do so, especially if the motion of moons or the length of the day require a week of a different length. Some worlds have opted to employ a week that matches the motion of their moons. On some worlds, such as Lacandia and Shandiana, this has resulted in a seven-day week anyway, because the principal moons of these worlds have cycles of this length. Other worlds, such as Humus, have moon cycles with a different length; on Humus, the Common Calendar has a five-day week with epagomenal days. Prometheus is a world that has intentionally chosen to discard numerous Earth-based standards including the seven-day week, and the Promethean Calendar has a six-day week as a part of the 360-day Promethean calendar.

Because the week is a very useful subdivision of time that is used for many recurring events, no world has chosen to employ a calendar that lacked some form of weekly division. Instead, some worlds have chosen to augment the week. The Martian Calendar has numbered weeks and the Mareenian Calendar has even given names to each week in an uninterrupted four-week cycle as well as numbering them. On Mareenia, it is common for a payment interval to specify a day of the week within a particular named week, for example, Monday in Blueweek. This is found to be much easier to remember than some circumlocutious expression such as “every fourth Monday starting from Year 386, First Month, fourteenth day”.

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