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|
|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|
|Lacandia||Lacandian Settlement Calendar||28161⁄87||281.701149||269.128813|
|Lacandian Perpetual Calendar||28161⁄87||281.701149||269.128813|
|Prometheus10||Promethean Calendar||360||360||360||10Artificial day (tidelocked world).|
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.
Determine leap years as follows:
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.
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.
|Last week of long years||96||22||23||24||25||26||27||28|
|Last week of short years||95||15||16||17||18||19||20||21|
|Last week of leap years||49||29||30||31||32||33||34||35|
|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.
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”.