This document is part of the Martian Time Boneyard. It was originally located at http://www.marsengineering.com/Calendar/Weeks.asp.
Author: Shaun Moss

Weeks

Lengths

The 7-day week dates back to ancient Mesopotamia, however, throughout history there have been several attempts by different leaders to introduce weeks of different lengths, of 4, 5, 6, 8, and 10 days. These attempts have all ultimately been abandoned due to lack of acceptance. For some as yet undefined reason, human society seems to naturally prefer a 7-day work-rest cycle.

The 7-day week is used worldwide, and as this is one of the few aspects of society that almost all humanity agrees on, many designers of Mars calendars have felt it prudent to similarly define a Martian week to be 7 sols. Another minor advantage to implementing a 7-sol Martian week is that the term 'fortnight', meaning 'fourteen nights', will continue to equal two weeks.

This choice of week length results in an attractive feature that our Earthly Gregorian calendar does not have. Almost all Martian months contain 28 sols - exactly 4 weeks per month - therefore a month can conveniently be divided into 4 weeks or 2 fortnights.

Names for Sols

Before naming the sols in the Martian week, it's worthwhile to investigate how our current days of the week got their names.

The days of the week were originally named by Persian astrologers for 7 celestial objects - the Sun, Moon, and the five planets known at that time (see this page for more info). The Egyptians also adopted this system, followed by the Hebrews, Arabs, Indians, Tibetans, Burmese, and Japanese. Here we have yet another curious mystery surrounding the week - not only the system of 7 days per week, but the system of naming them was adopted almost unanimously by many different cultures worldwide. Even the order in which the planets are represented is the same, with the first day named for the Sun, followed by the Moon, Mars, Mercury, Jupiter, Venus, and Saturn. The English day names feature the names of equivalent Norse gods.

Day names derived from celestial bodies are still used worldwide, and similarly to the 7-day week, it's perhaps wise to continue with an accepted system. Anyway, astronomically-derived names are colourful, interesting, and relevant for a spacefaring civilization.

We named the sols for the 7 most visible celestial objects in the Martian sky - the Sun, the two Martian moons, and the 4 planets closest to Mars: Earth, Venus, Mercury, and Jupiter:

This set of names has the advantage that they each begin with a different letter, which makes for easy abbreviations.

The order of the names comes from the Sun, followed by the moons in order of distance from Mars, followed by the four planets in order of shortest distance to Mars.

Synchronizing Weeks and Mirs

As every month except Ophiuchus contains 28 sols, which is exactly 4 weeks, whichever sol the mir begins with is the same sol that each month begins with. If a mir begins on Sunsol, the first sol of each month of that mir would therefore also be Sunsol. Thus each calendar page in that mir would basically be the same (as illustrated in the Calendar Pages section).

Synchronizing weeks with mirs means beginning each new mir with Sunsol, regardless of which sol came before. Because Ophiuchus has 24 or 25 sols, New Mir's Eve falls on Deimosol or Terrasol. By just skipping the rest of that week and beginning the new mir on Sunsol, we create a perpetual calendar. This means the same calendar can be re-used mir after mir.

With a perpetual calendar, determining the sol of the week from a date becomes trivial. Whatever the month or mir, the 1st, 8th, 15th, and 22nd sols of any month are Sunsols. The 2nd, 9th, 16th, and 23rd sols of any month are Phobosols, and so on. Scheduling monthly events is simplifed, for example, if payday is the last Mercurisol of the month, this is always the 27th; a PTA meeting on the 3rd Deimosol of the month is always on the 17th. If you agree to meet someone on the 25th of some month, you don't have to check the calendar to find out what sol that is, because the 25th of any month is Terrasol.

Weekends

The book of Genesis is often cited as the original source of the weekend. The story goes that "the Lord made the heavens and the earth, the sea and all that is in them, and rested on the seventh day; therefore the Lord blessed the sabbath day and made it holy". Moses told the Hebrews that it was forbidden to work on the Sabbath, the last day of the week, which was to be set aside for religious observances.

Sun-worshipping pagans, however, considered the 'day of the Sun' to be their holy day (holiday). The Roman Catholic Church changed the Christian holy day to Sunday around 1000AD, as a means of marketing Christianity to pagan cultures. Many western religious groups have since followed suit.

Society is adaptable, and in modern times most people have both the first and last days of the week free, such that either day (or neither) can be used as a holy day, according to preference. The system of designating two days per week as free days is in widespread usage, and I suspect most people would want to maintain this pattern on Mars.

However, a Mars calendar must not be biased towards any religion or culture, so we must also consider that Muslims regard Friday as their holy day, the sixth day of the week.

One possible solution is to allocate the last day of the week (Jovisol) as a free sol for the entire population, and one other sol per week can be chosen as free according to personal preference. Muslims can have Mercurisol or Venusol as free, Christians can have Sunsol as free, Buddhists can take sols off in accordance with the phases of Luna, and moody people can have a sol off when it they feel like it.