Submitted by mossy2100 on Tue, 04/25/2017 - 00:53

Should the calendar include weeks?

Weeks evolved from the average period between the four key lunar phases:

  1. 🌑 new moon
  2. 🌓 first quarter (waxing half moon)
  3. 🌕 full moon
  4. 🌗 third quarter (waning half moon)

Luna was once viewed as a big clock in the sky, with these distinct phases clearly visible to all. They indicated the beginning of new weeks, and determined things like when market days were held.

The average period between these lunar phases is 29.53 ÷ 4 = 7.38 days. Eventually this cycle was standardised to 7 days, after which weeks, just like months, were no longer synchronised with the lunar phases.

Weeks are important in Terran culture mainly because they define the work-rest cycle. The 7-day cycle has also become firmly cemented in many Terran cultures due to its use in religion, particularly the Abrahamic religions (Judaism, Christianity, and Islam). For example, the book of Genesis (the first book in the Christian Bible) says that God created the Universe in 6 days, then rested for 1 day. Following this, the 10 Commandments, found in the Hebrew and Christian Bibles, says to remember the Sabbath day and to “keep it holy”; to do all our work in 6 days, then rest for 1 day.

Martians will surely also want a cycle of roughly the same duration as a week, hopefully not for religious purposes, but certainly to define when everyone takes a break for 1 or 2 sols.

How many sols should be in a Martian week?

The 7-day week is one of the only things that humans agree on worldwide. Different cultures at different times have experimented with weeks of 6, 8, and 10 days, but today all of Earth uses the same 7-day cycle.

The Gregorian Calendar was developed to account for inaccuracies in the Julian Calendar that had caused it to drift away from the cycle of seasons. This was resolved by removing 10 days from the calendar, so that 4 October 1582 was followed by 15 October 1582. However, despite this change, the pattern of weeks was unaffected. The 7-day cycle continued as normal.

Since all Earth has settled on 7-day weeks, it’s reasonable to expect that this will also work for the Martians. The case can be made for 6-sol weeks (easy to divide by 2 or 3), 8-sol weeks (easy to divide by 2 or 4), or even 10-sol weeks (decimal, and easy to divide by 2 or 5), but the case for the 7-sol week is made stronger by the fact that most Martian months have 28 sols, and thus can be neatly divided into exactly 4 weeks of 7 sols each.

Also, a Martian week of 7 sols equals 7.19 days, which is rather elegantly the average of the Terran week of 7 days and the lunar week of 7.38 days.

Synchronising weeks and months

In the Darian and Utopian Calendars the last week in a short month is a short week of 6 sols; all others are long weeks of 7 sols. This may seem incongruous with the above comments regarding the regularity of 7-day weeks throughout Terran history, however, this small occasional adjustment (3 or 4 times a mir) enables weeks and months to be synchronised. The first sol of each mir, and the first sol of each month, coincide with the first sol of the week.

This produces a perpetual calendar, which means the calendar pages look almost identical every year. The Gregorian Calendar, by contrast, is not perpetual. There are 14 possible arrangements of the Gregorian Calendar, since a year can start on any day of the week, plus it can be a common year or a leap year. In a perpetual calendar, there are only two possible arrangements (short and long), and only 1 month is different, and only slightly, having an extra day (or sol). The World Calendar is the best known example of a perpetual calendar for Earth.

There may be opposition to 6-sol weeks, particularly among followers of Abrahamic religions, who consider the 7-day cycle holy and designate 1 day per week as a special day (although they disagree on which it should be; in Islam it’s Friday, in Judaism it’s Saturday, and in Christianity it’s Sunday). Others may object to the idea of losing 1 day of the weekend (if Martians still follow the conventional 5:2 work-rest pattern), although there’s an obvious solution to this: in short weeks, make the work week only 4 sols long and keep the 2-sol weekend.

Considering how established 7-day weeks have become on Earth, I originally only had 7-sol weeks in the calendar, i.e. weeks were decoupled from months and the calendar was not perpetual. The short weeks and perpetual calendar came from the Darian Calendar, and I incorporated this feature into the Utopian Calendar when Tom and I decided to make our calendars mathematically equivalent. The popularity of the Darian Calendar may be an indication that people are willing to accept short weeks on Mars, and, in any case, since we are attempting to create legacy-free societies on Luna and Mars, we should probably not attempt to strive for backwards compatibility with iron age religions, particularly if it produces a suboptimal calendar. Martian culture should be as legacy-free as possible.