World Building Question: What month is it?


Didn’t it feel like March just sailed by?  Isn’t it nice we’ve been having a temperate Ēostur-mōnaþ thus far? Am I the only one worried we’re going to have a viciously hot მკათათვე?  I’ve been working my way through periods of time with these world building questions, and it’s time to move from hours to weeks and now to months.  We skipped one unit of time that’s directly observable, the day, but we’re going to stop here on another that’s theoretically observable, the month.  I say theoretically as we’ve diverged slightly from the origins of the month, but that’s already getting ahead of ourselves.

Months are roughly based on moon cycles.  The period from full moon to full moon is roughly 29.5 days, and tracking the lunar cycle dates to at least the Paleolithic era.  This means that the concept of the month as a period of time is roughly as old as humanity’s concept of tracking time.  However, the idea of a month gets complicated as soon as we divide 365.25 by 29.5 and wind up with 12.4.  That is to say a year cannot be evenly divided into months as long as months are tied to lunar cycles, and a month tied to lunar cycles is going to be as off-center compared to the year as weeks are compared to months.  So what do we do?  On earth there are three answers: lunar calendars that will drift compared to the seasons, lunisolar calendars that add what we might call “leap months” to even everything out, and solar calendars that decouple months from lunar cycles.

Lunar calendars, such as the Islamic calendar, define a year as 354-355 days or 12 synodic lunar cycles (there are five lengths of lunar months that I’m not going to cover because, frankly, I don’t understand them).  The major effect of this is a drifting of Islamic holidays when compared to the Gregorian calendar.  Ramadan, the holy Islamic month of fasting, cycles backwards through the Gregorian calendar in roughly 34 year cycles.

Lunisolar calendars base the length of a month around the same synodic cycle, but make an attempt to adjust to the period of a year by providing extra days built in when needed.  In keeping with our religious calendar theme, the best known of these lunisolar calendars is the Hebrew calendar which adds an extra month to seven of the years in a 19 year cycle.  This is why, while Ramadan begins roughly 11 days earlier every year, Hanukkah reliably falls during the Gregorian month of December, though does shift between the beginning and end of the month.

Solar calendars are what most people reading this post are accustomed to.  The Gregorian/Christian calendar is solar.  Notice a trend, three major Abramic faiths, three majors calendar types?  I suspect an ethnographic study could be made of why the religions each chose the type of calendar they did, but this isn’t about ethnography.  The Gregorian calendar is, let’s face it, a mess.  But it’s a mess in the kind of way that fascinates me for world building, because it shows how different influences shape simple things.  Some highlights:

  • A significantly shorter month, which used to be the last month and thus had its length determined by how much time was needed to catch up to the solar year.  This is why leap days are still applied to February.
  • Four months named after an older calendar order, thus September thru December, the 9th through 12th months, have names that mean “7th Month,” “8th Month,” “9th Month,” and “10th Month.”  January and February were the 11th and 12th months.
  • Four months are named after gods (January, March, May, and June), two after emperors (July and August) and one month’s etymology is lost to time (April).

Random side note observation: with both hours and weeks we saw an attempt to decimalize them during the French Republic period.  Months?  They were fine with 12 of them, though of 30 days each with 5-6 bonus days at the end of the year, similar to the Mayan Wayeb’.

I’d normally be digging more into the origins of months, but here’s the thing.  Months are potentially a very human thing.  Many cultures independently came up with them, because the cycles of the moon are very obvious to the naked eye.  It’s the only object in the night sky that changes so dramatically.  And there’s just the one of it.  So if you’re world building a fictional civilization that’s earth based, they’ll probably have some concept of months, with the question being whether the calendar is Lunar, Lunisolar, Solar, or whether they keep both a solar calendar and a ceremonial lunar or lunisolar calendar, as the widespread adoption of the Gregorian calendar requires of practitioners of the Islamic and Jewish faiths.

Things become more troublesome when world building for a species not based on earth.  There are more variables to consider.  Is there a single frame of reference for a longer period of time, something between a day and a year?  Does it line up evenly with a year?  Do the locals care?  If there’s no obvious astrological point of reference, is the year subdivided in some other way?  By seasons?  Arbitrarily?  Mayans had 20 day months in their calendar tied to the solar year, chosen to evenly divide the year rather than tracking lunar phases.  Are there two moons and a complex series of calendars that include a solar calendar, prime-lunar calendar and secondary-lunar calendar?  Why do I think that last one would be fun to work out?  Just what would happen to a culture that had a strong lunar tradition if something catastrophic happened to their moon?  Why am I putting so many story ideas I want to use in these questions?

Let’s do the reverse world building wrap-up.  On my planet called earth, they have a moon that dominates the night sky, and goes through 29-ish day cycles.  They’ve long used these cycles as a unit of time, and now have calendars based roughly on the cycles, though with some fudging to keep up with the length of a year.

Some of the upcoming questions (and the intended topics) for this series:  What year is it (how years are numbered and when do they start)?  What’s for lunch (eating and mealtimes)?  Which way is the restaurant (directions)?

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