Potential Calendar Questions

[Raphael]

Until very recently, I didn't think much about my conworld's astronomy. Now I've thought a little bit more about it, and I'm currently leaning against giving them any major moons.

So, first 1) would that be plausible? I mean, if the planet is supposed to support life, intelligent life, technological societies, and all that, and if it's supposed to have stable seasons?

Now, if the answer to the first question is "yes", then that would leave me with no "obvious" time unit between a day and a year. Which leads to Question 2), would it still make sense for a culture that doesn't live to close to the Equator to divide the year into spring, summer, fall, and winter? As it turns out, I already have words for these in my main proto-naming-language, so the speakers of that language presumably lived in a temperate climate, but I haven't yet decided where their more modern descendants ended up. Now, if the culture lives in a place with stable seasons not too close to the Equator and does some amount of astronomical observation, would it, then, 3) make sense for them to treat midsummer and midwinter as pretty important dates?

[alice]

Unless there is enough gravity to keep the planet's axial inclination stable, this is probably not plausible.

[Ares Land]

Recent research suggest that the potential instability isn't as bad as it was supposed to. You can check here for the juicy details: http://barnesos.net/publications/papers ... .Earth.pdf
Basically, it's not quite as stable as Earth, and you still have variations of 10° or more, but over a longer timescale than suspected.

An interesting alternative would be to posit that the axis is indeed not too stable, and to figure out that, as they said in Jurassic Park, life finds a way. The adaptations could be fun to imagine.

In any case, axis tilt variations still occur on a scale of millions of years. Way more than a human lifetime, or even a civilization's lifetime. So, sadly, it looks like Game of Throne's climate antics are out.

Now, regarding your second question:
-- As for seasons, it all depends on how high the axias tilt is. If it's about the same as ours, the divisions will be similar. The four-season division maps with day lenght variation, so it would be plausible in the mid-latitudes, but there are a fair amount of possible variations: https://en.wikipedia.org/wiki/Season#Ot ... _reckoning (I like the six seasons model myself).

As for midsummer and midwinter, it could certainly make sense. For midsummer, for instance, a culture in the mid-latitudes growing an annual plant similar to wheat will most certainly notice than when the days are very long, it'll soon be time to harvest. Though they could focus on the equinoxes. (For that matter, plenty of cultures have the year begin in fall, presumably when all of the harvest is in and the state can start taxing the peasants...)
If you know any farmers or gardeners, you'll notice that they are extremely attuned to seasonal variations.

As for intermediate periods, there are plenty of alternatives to moons: other planets (as in Mesoamerica), floods (as in Egypt), bright stars (as in Egypt, again) or constellation (as in China) are all very good alternatives.

[Raphael]

Ah, bummer. Thank you. Seems like to keep things relatively Earth-like, I'll have to go with one more or less Earth's-Moon-like moon. I wish I could have done a somewhat more original astronomy.

[Ares Land]

If I may offer some advice, I'd say keep the planet without a moon. The counterintuitive thing about conworlding is that sometimes you just need to embrace the implausibility.

There are plenty of ways to handwave the stability thing. You can just assume that the axis tilt variation aren't so bad (there's even some research to support that option). Or place a gas giant nearby, that's definitely going to do something to the axial tilt (you don't have the orbital simulation resources to figure out what the effects are, exactly, but, hey, nobody does either).

The counterintuitive thing, I think, is that that sort of constraint are helpful, really.

Let's take an example. We start with a moonless planet. Let's add the gas giant, just in case. That kind of fixes your calendar problem: the gas giant will be very noticeable. For added fun, let's place it further away from the Sun than your planet, so you get retrograde motion. That neatly takes care of your calendar problem, BTW. (Your people will notice something brighter than Venus that moves backwards every two years or so) .

In addition, let's say that even with the gas giant stabilizing things, the axis varies from 0° to 40° over ten million of years. So your planet's just out of a huge ice age when only a tiny band around the equator was inhabitable. This means you get megafauna at all latitudes :all species evolved together in the habitable zones, so all animals are familiar with humans: no mass-killings of mammoth or wooly rhinoceroses. Oh, and animals must adapt to varying conditions, so mammoth and elephants are the same species really, they just shed all of their fur when it's hot.
You could just say that sapients arised during a period of chaotic axis variation. Ecological disruption is excellent for species formation. Their civilization is doomed eventually, but that's ten of thousands of years in the future. For added fun, let's say they went through that process already. So expect lots of ominous strange ruins and incinerated artifacts at the bottom of glacial lakes. Did they try to warn the next civilization about the axial tilt thing? Excellent. Strange hieroglyphic warnings in abandoned, doomed buildings make for excellent local color.
(Or, as in Helliconia, there are several sentient species, each adapted to a particular axial orientation...)

The good thing is, you don't have to worry about all of this stuff right away. Conworlding is an iterative process anyway. So you can begin by assuming the planet is Earthlike, then when inspiration flags and you have to write about the long and protacted war between Blandia and Boringistan, bring out the war mammoths and the 50,000 years old nuclear waste barrels. But, basically, by placing a slightly implausible element, you get lots of local color free of cost.

[elemtilas]

If I may offer some advice, I'd say keep the planet without a moon. The counterintuitive thing about conworlding is that sometimes you just need to embrace the implausibility.

I complete concur with this.

Ah, bummer. Thank you. Seems like to keep things relatively Earth-like, I'll have to go with one more or less Earth's-Moon-like moon. I wish I could have done a somewhat more original astronomy.

If you want an Earth-like planet that doesn't have a Moon, well, you just do that! It's been a growing trend, among worldbuilders as among language inventors, that, for some strange reason, everything must be plausible and realistic. As much as Realism School fans decry Star Wars I find it a source of wonder that inhabitable planets can have three suns and huge moons and all the rest.

I think the lesson here is to put science at yóur service --- rather than to conceive your world in the service of science.

[alice]

If you want an Earth-like planet that doesn't have a Moon, well, you just do that! It's been a growing trend, among worldbuilders as among language inventors, that, for some strange reason, everything must be plausible and realistic. As much as Realism School fans decry Star Wars I find it a source of wonder that inhabitable planets can have three suns and huge moons and all the rest.

I think the lesson here is to put science at yóur service --- rather than to conceive your world in the service of science.

Strict adherence to "plausibility" and "realism" can be overly limiting, and can lead to nervous paranoia, but you have to be careful not to go too far in the other direction, otherwise you'll end up with no limitations at all. I think a maximum of one ass-pull per con-thing is sensible, or two with a lot of caution. This probably deserves its own thread.

[elemtilas]

If you want an Earth-like planet that doesn't have a Moon, well, you just do that! It's been a growing trend, among worldbuilders as among language inventors, that, for some strange reason, everything must be plausible and realistic. As much as Realism School fans decry Star Wars I find it a source of wonder that inhabitable planets can have three suns and huge moons and all the rest.

I think the lesson here is to put science at yóur service --- rather than to conceive your world in the service of science.

Strict adherence to "plausibility" and "realism" can be overly limiting, and can lead to nervous paranoia, but you have to be careful not to go too far in the other direction, otherwise you'll end up with no limitations at all. I think a maximum of one ass-pull per con-thing is sensible, or two with a lot of caution. This probably deserves its own thread.

True that! Though in my opinion at least, that limitation is rather high! Otherwise, fantasy & sci-fi wouldn't work at all!

[Raphael]

Oh, that's a lot of food for thought. Thank you all! Not at all sure where this will go.

[Moose-tache]

I think it is far from given that a planet without a moon has unstable obliquity. In our solar system there are four rocky planets. One has stable obliquity, one has unstable obliquity (sort of, more on that later), and two are under so much tidal effect that they're fairly useless for studying obliquity. That's a pretty terrible data set. And within that data is a large number of variables. To put it bluntly, Mars sucks. It has no sizable magnetic field, barely any atmosphere and a deficiency of nitrogen, no plate tectonics and probably no lithosphere, and most importantly here, it's about the size of a grape. In fact, for the purposes of our discussion, Mars is not an Earth-like planet, since I doubt Raphael was planning to set his civilization on a planet with 0.38g surface gravity.

Laskar claims to have developed computer models that show that Earth's obliquity would be highly unstable without the moon. But mathematical models are only as good as the variables you know to account for. Models in a vacuum quickly become circular. Think of it this way. If you had only ever seen two animals, an ox and a ferret, you would quickly figure out that only an ox can pull a wheeled cart. Does that mean that without an ox, wheels do not function? Mathematical models would say that yes, a ferret is far too small so only an ox could do it. But we know that's not true. A horse can pull a cart, or a llama, or maybe a really strong pig. Later models have not replicated the same results that LAskar came up with. This doesn't mean he is wrong, or that math doesn't real. It just means that we cannot say with confidence, that no moon equals unstable obliquity.

OK, so we may or may not get unstable obliquity without a moon. I'm not convinced that we would, but what if we do? What if we ended up with Martian obliquity? Here is a record of Mars' recent changes in obliquity:

25 mya to 12 mya: increase from ~25 degrees to ~38 degrees
12 mya to 5.5 mya: stable at ~38 degrees
5.5 mya to 3 mya: steep drop from ~38 to ~25 degrees
3 mya to present: stable at ~25 degrees

So we have entire epochs of stable obliquity, punctuated by epochs of change, some of which are rapid and some of which are fairly slow. I realize that life is fragile. David Attenborough told me so. But I find it hard to believe that a change in tilt over two and a half million years is an insurmountable barrier for complex life or human civilization.

[Moose-tache]

New post because new topic...

As for calendars, you don't need a moon to have some measurement between "day" and "year." You certainly don't need a moon to tell you what season it is. Here are some options:

The obvious one is stars. Different stars appear at different times of year, as the planet makes its way around its parent star. For example, Orion is visible from November to February. This will change over time, but who cares? That didn't stop people from naming months after things that happen during certain times of year. You could even have constellation cycles that become completely unstuck from their origin. One "Orion" could be a four month period in winter, regardless of whether or not you can see Orion. You could have a whole series of stellar markers that appear at predictable times throughout the year, and then use them to mark time independently from the movement of stars.

The next one is planets. The Mayan calendar makes a meal of the movements of Venus, and your solar system could have some very dramatic planets indeed. A large planet with a high albedo slightly inside your planet's orbit (basically extra-Venus) could easily be bright enough to stand out sharply against the other stars, and its movements against that background would be pretty obvious. Planetary orbits also will not line up with the solar year, but it still doesn't matter. Unless it does! A planet in some kind of resonant harmony with your planet could actually provide a near-perfect solar calendar without ever having to count days.

Lastly, we have market cycles. In several cultures, markets happen on a regular schedule, and this creates natural rhythms of daily life every four or five or eight days, or however long it is. You could base these cycles on the length of a whaling voyage, or the life cycle of a basil plant. Basically, it's a solar calendar that requires counting days, and will therefore very slowly move out of synch. Again, the theme is: nobody cares. Calendars can be fixed manually, or their inaccuracies can be ignored.

Raphael, I would actually love to see you make a calendar that completely ignores the moon because there isn't one.

[xxx]

calendars reflect needs, our seasonal calendars are relics of our farming ancestors...

I wonder what our calendar would be like for a people with a different food supply...

another question about calendars is when do they begin: what date to take for the base of the annual tally...

[Raphael]

Thank you, Moose, that's very informative!

xxx: yes, the seasons are more important for farmers than for most non-farmers, but to some extent seasonal changes in the weather probably matter for everyone who spends more time outside than I do.