Thoughts on conworld calendars

Yes, we’re still playing and yes, I have to get a lot of logs up. Those are as much for me to have a reference as anything else, and I feel lazy.

But this isn’t about that.

Dave Ripton posted that one of his players asked about the Archontean Calendar in his game, and it will come as no surprise to any of my players to know that this player was me. (I was looking at the “Birthday” blank in GCS.)

In my nerdy conworld/conlang creation, I have learned a few things about our calendar that are important. When you get down to all of it, we’re talking about four units of time. I’ll go through each one and explain why people have used them and how we derived them:

Day: This is how long it takes the Earth to make a full revolution. Fantasy games leave this at the same as the Earth day, and that’s the best way to do it. (I advocate making mostly Earthlike worlds to let them fade into the background and focus on the game or story at-hand.) Anyways, our sleep patterns are keyed to this, as humans have poor night vision and thus can’t work at night. (We got good color vision to compensate.) Any cat owner will understand that our feline masters do not have their sleep keyed to this, or at least not as closely.

Week: The week has had a lot of variance, but it is more-or-less how long it takes to go through each quarter of the moon cycle. (See the month for more.) What is it for? Well, it comes from ancient Babylon, and we use it now to handle rest days. (I check Wikipedia, and it turns out that this was the case even in Babylon. I did not know that until checking.) This passed to the Jews, a sect of which, the Christians, who became the official religion of the Roman Empire. This replaced the eight-day Roman week, which was important for when markets were open. That last function transferred over to the Babylonian/Jewish week that medieval Europe adopted, and is going to be important for a game inspired by that world.

Month: This is about how long it takes for the Moon to circle the Earth. Humans have long handled accounting business monthly; it was how often Roman soldiers got paid.

Year: This is how long it takes the Earth to circle the Sun. Agricultural events happen yearly.

Like I said for the day, I encourage conworlds for fantasy games to be more-or-less Earthlike to keep the weirdness from taking center stage. This means that days are about 24 hours and years are about 365.242 days. You can vary the last one a bit, but it will always be around this. Touch the first one at your peril. If the world has axial tilt—and not having it would be weird and might take center stage in play—the year will be important for weather and crops, and the day is always going to be important for sleep.

The real ones of variance are going to be the week and the month. The biggest question people making these worlds should ask themselves is why do these worlds have them at all, as they’re not that important biologically, especially the week. In humans, we’re really talking about only the menstrual cycle as having a length about the same as a month, but given the importance of that to reproduction, it seems likely that there will be something that takes around 29.5 days (the synodic month, which is how long it takes from new moon to new moon) to which peoples will key at least that part of their lives, and possibly other parts as a result. A moon is a good thing to pick, since tidal effects are synched to this.

The week is most variable since it doesn’t outright correspond to some natural function. The Babylonians for some reason decided to make every seventh day some bullshit bad thing and not have everyone going all-out on it, and that passed on to the Jews and Christians, who then gave it to the Romans. (I’d apologize to any followers of the Babylonian religion if I felt bad about calling any supernatural occurrence bullshit. It’s bullshit. Get over it.) Markets and churches can reasonably have their more-often-than-monthly occurrences happen at about any length of time up to a half-a-month. (Any longer, and you’re just going to give yourself a headache for something that happens sometimes more than once a month but not always.)

Now for the quirkiness. The key issue is that days and months do not always add up to be a perfect year. A year has 365.242 days and 12.37 synodic months, after all, and even synodic months take up 29.53 days. We compensate for the issue of days and years not synching together with 97 intercalary days every 400 years (as in, every 4 years unless the year is evenly divisible by 100 and not by 400; for your world, 1-in-4 is much better to deal with).

The Romans, at least until Julius Caesar fixed things, had an intercalary month (Mercedonius) to deal with the months not equalling a year. Caesar ended this practice and set every month to have a fixed number of days, with only February varying, and redistributed some missing days to months that didn’t originally have 31 days. To give the rhyme we Latin students learned to deal with the weird Kalends/Nones/Ides system: “In March, July, October, May, the nones fall on the seventh day.” Those four months were the ones that originally were 31 days. And yes, I know about Augustus robbing February of a day when he renamed Sextilis after himself.

For my own fantasy world, I have a year be 360 days, with eleven 32-day months. Markets are keyed to the eight-day period between each quarter of the moon cycle. To deal with the remaining eight days (11 *32=352), I have an intercalary month every four years, implemented by royal decree. Every four years, the first of the year happens on the Vernal Equinox; some festivals are keyed to the equinoxes and solstices.

This was inspired by the pre-Julian Roman calendar, which, being a Latin speaker, I know fairly well, and the Jewish calendar, which is also lunisolar and is more regular than the Roman calendar but has month names that I don’t know. Like the old Roman calendar, the year starts on the first of spring.