Human Years

As it is the start of 2025, and I am mostly caught up with my short story submissions I am going to start back up with Worldbuild Wednesday.

Because it’s the start of a new year I think it’s time to talk about time. I have found worldbuilders are very split on the subject of time. Some simply import the Gregorian, others use the Julian for it is different, others borrow from the Islamic or Chinese because the aforementioned is ‘to western’. Often with at most cosmetic swap of changing names and days of the week. However this often ignores the rest of the world.

This is especially disappointing when the world is designed to be independent of earth. I have seen worldbuilders design and develop new sentient creatures unrelated to humanity with myths, governments, holidays and even songs. Yet they used the Gregorian Calendar; it was rather disappointing.

To prevent myself from falling into that situation with Slonminma, or as it was called Sonomia, thus I did what a lot of worldbuilders who are looking for some math do dig into Artifexian’s videos. He has three good videos on Solar, Lunar and Lunisolar calendars. While I will leave the mechanics to him, I will summarize. Solar Calendars Track the sun and a year is equal to the time it takes for a planet to orbit the sun. Lunar tracks the moon, meaning a year is however many moons long one wants it to be, solar location be forgotten. Lunisolar tracks both which means math gets complicated with realistic numbers, sometimes with leap months, sometimes with leap days, sometimes both.

However there is an issue that Artifexian doesn’t comment on, I call it Age Drift. Take Slonminma as the example. Should I use a solar calendar the year would be 707 days long with a leap day every other year and a second one every 30 or so. If I declare this as a year, and a character is 10. How old are they on Earth?

To run the math quick, we start with what we have for the Slonminma Year.

Since we know Earth has 365.25 days a year, we can divide to make this a year to year comparison.

Now just plug in my 10 years old on Slonminma:

Which isn’t what people would expect. This 10 year old woman could be married, to an 11 year old man (that would be 21-ish) and looking to buy a house, as their second kid is on the way. Now I may not be a woman, but I suspect having a kid by 10 isn’t posshsible. Having one or two by 19, that’s a different story. Which is Age Drift. This gets more pronounced the older we go. Take 37, which is an established man on earth, and a grandfather on Slonminma for that would be around 72 Earth years.

I will concede that in the grand scheme of most stories ages aren’t important. Using comparative terms such as, boy, man, gramps, etc (for those of us without easy access to visual clues) to give the audience the comparison. However should it ever need to come up in dialog things may get a bit complicated. Say I’ve established a man is well, a man. Not a young man but not an old man. Just a man. He is going to complain about being called old by a younger character. Using Slonminma as the case, I run the math and he is 18. So I have him say “I’m not even 20 yet!” This works in world, and fits the flow of conversation.

Yet the reader knows he was proud when his daughter got married, is looking forward to being a grandfather in a few months, can’t wait for his son to finally pass into man hood, and yet is somehow under 20. Some readers can hand wave this away, some can’t. Thus I would recommend avoiding the issue.

To sanity check oneself I’d calculate the age drift as a percentage which is the following continuation to the math above. The reason I recommend using it as a percentage is to highlight how far off the years get over a century. A drift of 5% means 5 years every century. The formula is below.

Now all this math is only easy if a day is a day. If a day is much less or much more than a day, say less than 20 or more than 28 Earth hours things get more complicated. As now either orbital mechanic math or some interesting conversions get added to the pile, not to mention the other various impacts adjusting the day length can have.

Warning aside, when I run the number for Slonminma’s solar year; the fomula gives us 93.7%. Which isn’t ideal. I would be drifting almost 94 years every century. Thus the question: how did I solve the age drift for Slonminma?

I went with a lunar calendar, meaning my month would be one moon, or 33 days long, and went with 11 months. That got me extremely close, and for most worldbuilders having a calendar that is different and within a 1% drift will be good enough. However, I wanted to go even further. So I made the changes of seasons days ‘outside of time’ in the sense that the calendar doesn’t track or count them. If we did this on Earth it would be March 19, Spring Equinox, March 20th, March 21st, so on and so forth. I did this largely for cultural and religious reasons, but also magical reasons. For one of the two magic systems is somewhat tied to the seasons.

By adding this solar event to my lunar calendar means each year would end up being 365 days long, or 366 every 16th year. Which is just about perfect when compared back to the 365.25 of Earth. Giving a Drift Percentage of 0.05%. Which is one year every 2,000.

However this adds in another ‘problem’. That being the moon I’m referencing for the month doesn’t stop existing for the solstices and equinoxes. Likewise it doesn’t freeze in it’s orbit for a day. In reality this wasn’t much of an issue since the moon orbits slightly longer than 33 days, it’s 33.17 to be specific. Thus the 11 months adds about 2 days anyway (1.87 for the pedantic). Meaning 365 days to complete 11 moon cycles is more accurate than the 363 I started with. To solve this and lock back to the moon I subtract a day every eight years and a second every 16. This means the moon is at worse a full day off where the calendar says it should be at any given time. This does mean that every eight years the calendar days are 362, and every 16 it’s 361. By adding in this new subtraction does double my drift amount to 0.1% which is more than acceptable, as that is a year of difference per thousand.

Now my family has given me more than my fair share of grief for shortening the year on the ‘leap years’ rather than making it shorter than longer, and needing to put together spreadsheets and python scripts to verify my satisfaction with it. However I think this rather screwy calendar highlights the fact that worldbuilding can let the creator do what they want to get what they want out of their creation. I wanted something that would be unique, tied to the world it is coming from in a way where it couldn’t properly be separated; yet a calendar that keeps pace with the time on Earth to a degree where I will never have to worry about it, and I did it.

Now that the math has been mathed, at least with my world. The more interesting portion can be brought to task: Naming and organizing. Generally speaking this is a question of culture and history. I separate them here because they are different approaches to the topic. The Georgian for example draws form history as it was meant to be an update to the Julian, yes I will admit that’s a borderline criminal over simplification, which is why the two are so similar. Likewise the fact that the Orthodox Churches stuck with the4 Julian Calendar for their religious events and the civilian side adopts the Georgian. This shows how their culture influences the calendar.

The cultural influences can be highlighted with the month structure, and days of the week. Does the calendar have even weeks? Are there uneven chunks? are the days numbered or named? Does every day have a name or are they days of the week? Is the calendar global or local?

These questions much like the one about age drift, unlikely to have major impact on a story, does it matter if grandma was run over on Friday or Wednesday? Maybe, but it’s unlikely. Thus my recommendation is to have them on hand, but don’t expect them to use them.