How do you measure time on a tidelocked planet?

[Septimus]

Coming from an astrophysics background, I find this thread really interesting.

For the star duration (less than 100 millions years approximately as a yellow supergiant), I do not see another way than to hand wave the problem to either magic or advanced science (which are equivalent concepts). Close binary would mildly increase the duration, as two stars with equivalent summed luminosity will still be massive stars and the billion years of life expectancy is nowhere close. Furthermore, the OP seems to be locked on a RCB star, which is fine as it includes some interesting facts for the stated problem.

RCB stars are variable stars, with two modes of variability : one with small amplitude and quite predictable, and another with higher amplitude but quite unpredictable. These should be taken into account when we are considering the life forms that evolved on the planet and how to measure time.

The small but regular amplitude should be the basis of the time passing. For most RCB stars, it looks like the period is several tens of days, but with the cycle you might infer that it is measurable and take into account by observer to measure the time to pass. Up to you to define a convenient time, but a 28-day period is probably the right thing to catch-up on Earth equivalents. Then you can easily split it into 4 "weeks" of ascending/high/descending/low period of "sun", corresponding on weeks. Even if the sun is obscured by clouds most of the time, though time and observation, it is possible to find out these periods and implement them into a civilisation. For the shorter "day" period, I think the only solution would be to be based on the moon orbit, which might be noticeable, or calculated through an ephemeris. You can have something close to a day with that.

The second mode would impact the equivalent of seasons. The impact of a dramatic change of lights, and for an unknown length of time, would trigger various life events for the life form: plant-based life forms would induce fruition and possibly winter sleep, and animal-based form would follow this cycle with rampaging feeding at the beginning of the decrease and possible hibernation for several large creatures. Humans, or equivalent, would probably create mythologies around this second cycle, with dramatic measures to keep everyone alive. The possibility of winters that spans across years in between "summers" that last decades is in fact a very similar setting than the Iron Throne (btw, a colleague of mine tried to find a astrophysics case that would match that and a few issues, but you could hand wave the minor details).

Life forms would have different sleep pattern, most probably using tricks to have functioning body for a longer period of time, such as a brain would have halves work in cycles, one half working as the second half is resting, and then the reverse. Dolphins use this tricks for the their sleep if I remember correctly, and you could expand this to most life forms: animals would have a "quiet period" when each half is resting, with limited activities but still active. Humans could evolve in the same pattern, creating the need of period of time where they are "not here" but still active nevertheless. It would be similar to a early version of elves who never sleeps but meditate to recover their capabilities.

The revolution time of the planet would be irrelevant, as stars observation would be difficult, and the length is too long to be measure for short-lived creatures. But elfes and similar creatures might have such a long cycle and use it as their "racial" calendar to keep tracks of lasting events. Short-lived creature might then be aware of this cycle, and care about it (mostly in religion I guess), and ignore it completely.

Then, finally, there the question of the night face, and the wind it should create. Strong winds, equivalent to hurricane or more, should be common. It is the necessary requirement to have a functioning atmosphere on all the planet: the night face should be freezing cold, and even gas may condense if it is too cold. Wind may ensure a mixing between the two faces and distribute heat and cold. Night face would be still very cold, but not necessary to the point where nitrogen would become liquid. Atmospheric models may compute the necessary exchange rate, but it would be easier to have a working model, such as constant strong wind, with possibly period of very intense winds. That would impact the architecture of advanced civilisation, with strong foundations or caverns used as emergency covers. With a slow rotation, and hence small angular momentum, you will not have a strong dominating direction but then the system would be more complex, and unpredictable for the intelligent life forms.

[Aotrs Commander]

Coming from an astrophysics background, I find this thread really interesting.

For the star duration (less than 100 millions years approximately as a yellow supergiant), I do not see another way than to hand wave the problem to either magic or advanced science (which are equivalent concepts). Close binary would mildly increase the duration, as two stars with equivalent summed luminosity will still be massive stars and the billion years of life expectancy is nowhere close. Furthermore, the OP seems to be locked on a RCB star, which is fine as it includes some interesting facts for the stated problem.

Ultimately, it was the most approximately plausible basis for the concept of a nonpredictable period of extended solar dimming (i.e. a an extremely long "night"); still entails handwaving, but it was the "best fit."


RCB stars are variable stars, with two modes of variability : one with small amplitude and quite predictable, and another with higher amplitude but quite unpredictable. These should be taken into account when we are considering the life forms that evolved on the planet and how to measure time.

The small but regular amplitude should be the basis of the time passing. For most RCB stars, it looks like the period is several tens of days, but with the cycle you might infer that it is measurable and take into account by observer to measure the time to pass. Up to you to define a convenient time, but a 28-day period is probably the right thing to catch-up on Earth equivalents. Then you can easily split it into 4 "weeks" of ascending/high/descending/low period of "sun", corresponding on weeks. Even if the sun is obscured by clouds most of the time, though time and observation, it is possible to find out these periods and implement them into a civilisation. For the shorter "day" period, I think the only solution would be to be based on the moon orbit, which might be noticeable, or calculated through an ephemeris. You can have something close to a day with that.

The second mode would impact the equivalent of seasons. The impact of a dramatic change of lights, and for an unknown length of time, would trigger various life events for the life form: plant-based life forms would induce fruition and possibly winter sleep, and animal-based form would follow this cycle with rampaging feeding at the beginning of the decrease and possible hibernation for several large creatures. Humans, or equivalent, would probably create mythologies around this second cycle, with dramatic measures to keep everyone alive. The possibility of winters that spans across years in between "summers" that last decades is in fact a very similar setting than the Iron Throne (btw, a colleague of mine tried to find a astrophysics case that would match that and a few issues, but you could hand wave the minor details).

That is the high-concept of the world. It was partially inspired by (which I can now address directly since someone was able to idenfiy it) the Third Doctor Serial the Mutants. Basically, from the standpoint of a civilisation, that darkness would fall, the world would change around them in terrifying ways and they would be suddenly dealing with an influx of monsters (apparent and actual) coming from the night side. The conciet being that the periods between as of sufficient space that when it occurs, it fundamentally ends the civilisations, which never have developed to cope with them. (The very early concepts were an evenstar; a world whose metaphorical "fantasy novel series" would be at the twilight (both literal and metaphorical) of their civilisation, as it is overrun by the thing Things from the Darkness.)

As this is an entirely alien camapign world, elves as such do not exist, and by definition of the central concept, the races which develop civilisations cannot be long lived enough to retain living memory. Thus, there is a world strewn with runs of previous, unknown civilisations. The most advanced of these is tentatively placed slightly beyond 21st century Earth (pre-FTL and pre-space colonisation); just not quite advanced enough to survive such a Bad Happen.

(The idea of the paleolithic tribe and their campaign - the Long Walk - their migration across the world, along an ancient road (something they barely undestand) came later. Part of the appeal of that scenario is to have a people so primative that it can capitalise on using player ignorance of the setting to make for better exploration in a way you can't do otherwise.)

Life forms would have different sleep pattern, most probably using tricks to have functioning body for a longer period of time, such as a brain would have halves work in cycles, one half working as the second half is resting, and then the reverse. Dolphins use this tricks for the their sleep if I remember correctly, and you could expand this to most life forms: animals would have a "quiet period" when each half is resting, with limited activities but still active. Humans could evolve in the same pattern, creating the need of period of time where they are "not here" but still active nevertheless. It would be similar to a early version of elves who never sleeps but meditate to recover their capabilities.

I have decided, in the event, to tackle this by having many creature have a continuous cycle, but for sophont lifeforms in particualr, to have a period of, if not sleep, perhaps something closer to elven trance; not quite torpor, but, like, you say, a quiet period on significantly reduced activity. (While their brains clear all the neurotoxins.)

Then, finally, there the question of the night face, and the wind it should create. Strong winds, equivalent to hurricane or more, should be common. It is the necessary requirement to have a functioning atmosphere on all the planet: the night face should be freezing cold, and even gas may condense if it is too cold. Wind may ensure a mixing between the two faces and distribute heat and cold. Night face would be still very cold, but not necessary to the point where nitrogen would become liquid. Atmospheric models may compute the necessary exchange rate, but it would be easier to have a working model, such as constant strong wind, with possibly period of very intense winds. That would impact the architecture of advanced civilisation, with strong foundations or caverns used as emergency covers. With a slow rotation, and hence small angular momentum, you will not have a strong dominating direction but then the system would be more complex, and unpredictable for the intelligent life forms.

That part I did get (the night side having a large ocean was also in part because what I had read was that would liekly be a further temperature stabilising factor.)

You can see some of that applied in the so-far brief data compiled (written as an in-universe study by the Aotrs, as it might eventually be used as an entry in Bleakbane's Galaxy Guide with the sailed hover shells. (Italics indicate a placeholder name for the moment.) Yes, the first creatures that were created for Andorlaine were magical, in defiance of concept, but partically, the hover shell is an nod to a picture I drew when the idea of an entirely alien campaign world came to me decades ago and comb jellies were the inspiration for the creatures the Aotrs party would encounter on their sojourn there. (And incidently, providing a disconnected, but in-universe perspective to write about the world with comparatives.) That it enabled me to encompass the demon brains in the same group was icing on the cake.


Scaled Jellies: Subphylum of endothermic creatures with radial symmentry around twelve ribs joined at the bottom of the creature (or top, in the case of the shelled flyers). They have six arms, morphologically closest to those of cephalopods, though the suckers are signficantly smaller, denser and finer and not as readily apparent.

Believed to be initially aquatic with covergenant morphology to comb jellies, the phylum is theorhised to have developed scaley and then scutted skin and bones in tandem; the bones allowing heavier scutes to be mounted. It is not currently clear whether or how the scutes are shed, but it is theorhised to be accomplished in a manner analogous to terrestrial turtle or crododile shells is they are shed; they may be retained throughout the lfie like some dragon species, but this is not through to be as likely. The anchoring of the skeletal structure allows more powerful musculature, predating via harpoon-tipped arms rather than complete reliance on stinging cells; the harpoons in many forms are armed with apparatus which appears to have functioned somewhere between a stinging tricome (i.e. a stinging nettle sting) and a nematocyst (i.e. a jellyfish/comb jelly/ anemone cell). Monster brains retain only a vestigial harpoon/sting (analogously equivalent to a more reinforced fingernail) while ghost jellies appear to have lost the harpoon entirely, but retained the sting.

Single mouth/excretory oriface (dorsally located); some waste products “sweated” out via pores. On magical floating forms, “nostrils/breathing apapratus” are located around the mouth, leading to six lungs, more primative marine forms have gill openings here, but which are likewise provided with water flow by breathing-like pulsations of proto-lungs.

Single muscular “foot” at bottom of ribs allows very slow ground locomotion and also serves as a holdfast.

Primary sense appears to be vibrational/hearing via an advanced system of lateral-line-like mechanoreceptors and electroreceptors located across the entire body surface. In combination with additional organ sensors, these grant a high kinesthetic sense. Six antennae (fillamented/feathered) appear to serve as a directional olfactory system and also may act as supplementary mechanoreceptors. Skin receptors on the skin and on the surface extremely developed tacile sense.

Vision is a secondary sense, provided by a series of eyespots, two rings, one between each rib segement on marine forms. On magical floating forms, at the front of the creature, a slight bulge houses additional eyespots on the upper ring, forming a diamond pattern with the top-most eyespot being part of the ring. Shelled flyers instead have developed more acute vision, transforming front two eye spots into eyes on rectractable stalks and losing the rest of the upper ring, while the lower eyespots have become centrally-located around the creature’s centre. Eyespots, while relatively simple (having no pupils) apparently have some ability to distinguish colour on some level, as evidenced by bioluminent nodules running down the line of the ribs and in some form, tentacles. Shelled flyers (observed) and monster brains appear to have relatively few of these nodules and use them infrequently. (Though it is speculated that shelled flyers may use theirs more frequently when mating.)

High animal intelligence observed in marine forms (approximated at canine- to octopus- perhaps higher) and lesser demon brains. Ghost jellies are sophont; demon brains are expected to be both sophont and highly intelligent from the differences in their morphology from the lesser demon brains. This is likely an emergant property of the complex nervous system created by the numerous, decentralised sensory organs. (This complexity is also potentially a cause of the evolution of the magical flight organs in the magical floating forms.) Shelled flyers, which appear to generally have more specialised diets, appear to show generally lower intelligence, especially in non-predatory forms; though not enough samples have been studied to say whether this is consistently true of their entire order.

Magical floating forms possess two organs at the rear which provide magical locomotion via levitation. Flight is suggested to have possibly developed as a method to escape predators in the acquatic environment (as terrestrial flying fish). These organs appear to have lost their original function in the monster brains, being re-purposed to service the eusocial controlling magics.

Shelled flyers have developed scuted skin into a hard shell. The mouth is now located on the ventral side; locations of organs suggest indicates that they evolutionarily inverted their body plan as they adapted to flight. Sailed hover-shells additionally have adapted two pairs of tentacles with webbing between that act as a retractable sail, allowing them to move downwind with significant ease; notably these forms with their reduced arms appear to be predominatly non-predatory.

Ghost jellies appear to have lost their scaled scuttes altogether, leaving only thin skin. This may or may not be translucent or semi-translucent. The ghost-like form encountered appeared to have translucent skin, but no living specimen has been observed. The observed deceased specimen’s skin was not translucent, but may have opaqued with mummification.

[Septimus]

You seemed to have studied your case a lot lol ;) I had assumed a nearly human life form for the exercice, so several of my comments might not apply for a "too-much" alien life form.

One of the things to be taken into account is that the "nights" are actually unpredictable in length but also in magnitude. You can imagine to have "winters" that last a few months with still light as the sun is on low power but still visible, and winters that last years of blackout darkness. A daylight civilisation might endure several winters before "The One" that destroys everything and press the reset button. That would create even more myths about the "darkness that destroy".

Also, as light is nearly always present on the daylight half, sight would be the most useful sense for animals, and a drop in the ambiant light would have more effects on the life forms than on our world where a large fraction of the animals are nocturnal. Adaptation of night vision would be extremely rare, and reserved to subterranean species, invaders from the night side, or specific species from the penumbral circle.

Large oceans are indeed a stabilisation factor, whereas they are in the night or in day faces. It makes sense to have most of the night face a global ocean, as the consequence of the meteorite impact that reduce planet's angular momentum to nearly 0. Such an impact, if you consider planetary physics would have created secondary ripples on the antipodes, in the day face. Such example are found on Mercury and Mimas (Saturn's satellite). You can expect to have a large landscape of the day face with large and deep canyons and cliffs, over a tumultuous ocean (don't forget the strong winds).

You might want also to look at the kind of volcanism the planet has: either with tectonic, such as Earth, or fixed crust. The presence of a closer moon would mean more active volcanism, but tectonic has the particularity to reset the surface from time to time, whereas fixed crust would mean very large volcanos on hot spots (think Mars' volcano who are 30 km high).

[Lord Torath]

You might want also to look at the kind of volcanism the planet has: either with tectonic, such as Earth, or fixed crust. The presence of a closer moon would mean more active volcanism, but tectonic has the particularity to reset the surface from time to time, whereas fixed crust would mean very large volcanos on hot spots (think Mars' volcano who are 30 km high).

I presume you mean the moon would cause move volcanoes via tides acting on the planet? I did some math a few posts back showing that the tidal force exerted by the moon would be identical to that created by Luna here on Earth. The moon orbits much closer to Andorlaine than Luna does to Earth, but it has the same apparent diameter. Assuming the same density (AOTRS Commander hasn't commented on the density of the moon, that I can recall), the distance cubed term cancels out with the 1/diameter cubed for the moon's volume (and hence, mass) term resulting in the same tidal forces. It seems to me that a smaller moon will generally tend to be less dense than a larger one, since there is less gravity pulling everything to the center, which would tend to result in weaker tides, not stronger ones.

Those tidal forces will move much more slowly on Andorlaine, of course, since it is entirely dependent on the orbital speed of the moon, since Andorlaine's rotational speed is effectively zero (one rotation every 1300 years or so). So the tides last a day and a half instead of 6 hours. I will admit I don't know what effect that slower tide will have. On the one hand, it might have a stronger effect on slower-flowing material like magma, but on the other hand, the closer to the core of the planet, the smaller the tidal force from the moon.

[Aotrs Commander]

You seemed to have studied your case a lot lol ;)

I did spend several months hashing out as much as I could within the region of "statistically high unlikely, but not statistically impossible" as much as possible. Aside from the hand-wavy sun lifetime, the only other area I had to resort to "we don't know/something did it" was stellar wind, because I couldb't even find the calculations to estimate it. (That actually stalled me out for a good long while.)

I had assumed a nearly human life form for the exercice, so several of my comments might not apply for a "too-much" alien life form.

There will be creatures that are humanoid, certainly (as in bipedal stance, two arms two legs and a head), though beyond that, the point was to not have just have human-knobbly-forehead aliens. But at the same time split the difference of not being SO alien (like a whole party of ghost jellies or something) it becomes difficult to run a campaign with. As I said to some folk on the speculative evolution rediit where I alos posted this, there is a level of practicality required that you can get away without when writing something from a purely narrative or documentory format. The protagonists species have to be within spitting difference so the PLAYERS can have some understanding, so you can't got too far afield. (Particularly with regard to senses; how would you even describe to the players the world as perceived through something whose primary sense is electromagnetism or something.)

It's a hard needle to thread, else I'd have got further than I have.

(As it is, my great ambitions for the year - I wrote up a list of things and goals to try and make some progress towards - have met with brick wall after brick wall at some point (both work and play); forcing me to split my focus all over the place, which has been frustrating.)

One of the things to be taken into account is that the "nights" are actually unpredictable in length but also in magnitude. You can imagine to have "winters" that last a few months with still light as the sun is on low power but still visible, and winters that last years of blackout darkness. A daylight civilisation might endure several winters before "The One" that destroys everything and press the reset button. That would create even more myths about the "darkness that destroy".

Also, as light is nearly always present on the daylight half, sight would be the most useful sense for animals, and a drop in the ambiant light would have more effects on the life forms than on our world where a large fraction of the animals are nocturnal. Adaptation of night vision would be extremely rare, and reserved to subterranean species, invaders from the night side, or specific species from the penumbral circle.

Large oceans are indeed a stabilisation factor, whereas they are in the night or in day faces. It makes sense to have most of the night face a global ocean, as the consequence of the meteorite impact that reduce planet's angular momentum to nearly 0. Such an impact, if you consider planetary physics would have created secondary ripples on the antipodes, in the day face. Such example are found on Mercury and Mimas (Saturn's satellite). You can expect to have a large landscape of the day face with large and deep canyons and cliffs, over a tumultuous ocean (don't forget the strong winds).

That's all useful to know; a landscape of canyons and cliffs is also very useful to have, both on a cinematic and practical level. A big enough ravines could form something of a natural barrier to pre-industrial species, which would exascerabate the extinction pronlems.

You might want also to look at the kind of volcanism the planet has: either with tectonic, such as Earth, or fixed crust. The presence of a closer moon would mean more active volcanism, but tectonic has the particularity to reset the surface from time to time, whereas fixed crust would mean very large volcanos on hot spots (think Mars' volcano who are 30 km high).

Tectonic, I think, after doing some more research is going to be the approach (aggrevated by the relatively new presense of the moon, which will probably only be around for a few millon years, but that's more than enough to serve the purpose on the lifetime of cilivsations). So some tectonic shifting, which also will hopefully help the canyons and cliffs a bit. The idea of some places drifting very slowly Into The Darkness was other narrative hook I liked, and tectonics and some tide-unlocking (however relatively marginal) from the captured moon somewhat facilitate that.

I presume you mean the moon would cause move volcanoes via tides acting on the planet? I did some math a few posts back showing that the tidal force exerted by the moon would be identical to that created by Luna here on Earth. The moon orbits much closer to Andorlaine than Luna does to Earth, but it has the same apparent diameter. Assuming the same density (AOTRS Commander hasn't commented on the density of the moon, that I can recall), the distance cubed term cancels out with the 1/diameter cubed for the moon's volume (and hence, mass) term resulting in the same tidal forces. It seems to me that a smaller moon will generally tend to be less dense than a larger one, since there is less gravity pulling everything to the center, which would tend to result in weaker tides, not stronger ones.

Those tidal forces will move much more slowly on Andorlaine, of course, since it is entirely dependent on the orbital speed of the moon, since Andorlaine's rotational speed is effectively zero (one rotation every 1300 years or so). So the tides last a day and a half instead of 6 hours. I will admit I don't know what effect that slower tide will have. On the one hand, it might have a stronger effect on slower-flowing material like magma, but on the other hand, the closer to the core of the planet, the smaller the tidal force from the moon.

To my calculations, the tidal forces are roughly the same yes. (By my calculations, Andorlaine's moon imparts about 94% of the acceleration Luna imparts to Earth.)

It's actually slightly denser, since density is due to composition, not size (and it's a "recent" capture, ejected from something else). Especially being so relatively small, as well, composition is a higher factor.

For the record, 609km diameter, density of 3650kg/m³ (to Luna's 3350kg/m³), though due to the small size the surface gravity is very low (0.063g).

[Septimus]

...

My bad, I misread your message. Yes, tide intensity would be the same, but longer period would reduce the amount of energy transferred I think, so volcanism would be lower, with the caveat that not all the internal energy comes from tides, as radioactive decay is also a major provider of heat (in the case of Earth). So actually volcanism is moot point and I was wrong: it can be adjusted with lower/higher internal radioactivity to fit the setting wish list.

[Septimus]

I did spend several months hashing out as much as I could within the region of "statistically high unlikely, but not statistically impossible" as much as possible. Aside from the hand-wavy sun lifetime, the only other area I had to resort to "we don't know/something did it" was stellar wind, because I couldb't even find the calculations to estimate it. (That actually stalled me out for a good long while.)

Solar winds are difficult to model because we lack observations on something else than the Sun ^^
RCB giants are supposed to have significantly larger winds, something like a thousand to tens of thousands stronger winds. However, its impact decreases in square of the distance, hence also in thousand decrease factor. It might then be more or less the same than on Earth. It also depends on the strength of the magnetosphere of the planet, which in turn mostly depends on how much liquid the internal core is, and is related to volcanism. On the other hand, RCB have less hydrogen and more heavy elements in their photosphere, so solar eruptions (which are non isotropic) might have more impacts on the planet than sun's eruption. It may prevent development of advanced technology (on the day side), but should not have strong impact on life form (unless you want so), aside accelerating the evolution process.

There will be creatures that are humanoid, certainly (as in bipedal stance, two arms two legs and a head), though beyond that, the point was to not have just have human-knobbly-forehead aliens. But at the same time split the difference of not being SO alien (like a whole party of ghost jellies or something) it becomes difficult to run a campaign with. As I said to some folk on the speculative evolution rediit where I alos posted this, there is a level of practicality required that you can get away without when writing something from a purely narrative or documentory format. The protagonists species have to be within spitting difference so the PLAYERS can have some understanding, so you can't got too far afield. (Particularly with regard to senses; how would you even describe to the players the world as perceived through something whose primary sense is electromagnetism or something.)

It's a hard needle to thread, else I'd have got further than I have.

I agree, alien is fine, but if you want players then it should not be too alien ;)

Tectonic, I think, after doing some more research is going to be the approach (aggrevated by the relatively new presense of the moon, which will probably only be around for a few millon years, but that's more than enough to serve the purpose on the lifetime of cilivsations). So some tectonic shifting, which also will hopefully help the canyons and cliffs a bit. The idea of some places drifting very slowly Into The Darkness was other narrative hook I liked, and tectonics and some tide-unlocking (however relatively marginal) from the captured moon somewhat facilitate that.

Yes, you're right: the recent adjunction of the moon would change the tide lock process, exchanging angular momentum. However, it might accelerate or decelerate rotation speed, and you might have a cataclysmic impact in the end, or the escape of the moon, depending the configuration.

[SouthpawSoldier]

Have any of you fine folks read Nightfall by Asimov? Details a culture in a similar situation to what OP describes. They aren't tidally locked, though; the planet orbits multiple stars, and they track time based on which suns are where in the sky.

Book details events when the culture experiences its first true nightime, with no suns in the sky.

[Palanan]

Originally Posted by Aotrs Commander
As it is, my great ambitions for the year - I wrote up a list of things and goals to try and make some progress towards - have met with brick wall after brick wall at some point (both work and play); forcing me to split my focus all over the place, which has been frustrating.

For what it’s worth, I know exactly how this feels.

Originally Posted by SouthpawSoldier
Have any of you fine folks read Nightfall by Asimov? Details a culture in a similar situation to what OP describes. They aren't tidally locked, though; the planet orbits multiple stars, and they track time based on which suns are where in the sky.

Book details events when the culture experiences its first true nightime, with no suns in the sky.

Yup, this parallel occurred to me as well, just didn’t have the bandwith to comment.

[Cinder39134]

There are prevailing winds from the night side to the day side, and the land is uneven. That suggests to me that you could have storm systems swept along with the prevailing winds. If their passing disturbed the region of the night side antipodal to the sun in the right way, a storm leaving might cause another to be made, and leave at a different direction, in some sort of periodic way. Basically, if the weather changes (and we know it does since you mentioned that it rains sometimes), maybe the conditions of the planet are right for massive storm systems to periodically sweep through at more or less consistent intervals, which would make a natural landmark for time to be set by? I don't know if that would be consistent with every part of the setup but it might make for something for natural cycles to be based off of (for example, storms throwing plant seeds everywhere for them to grow, so the plant would evolve to be ready to spread its seeds at that time) which would then solve most of the rest of the problem.

[Ashtagon]

You have no day/night cycle, and no seasons (or at least, no hot/cold cycle). It's cloudy enough that astronomy won't ever really be a thing. Wind patterns are consistent and not cyclical.

So, counter question: How prehistoric is this planet's moon? Because without tides, I'd question whether land life could even evolve. Fish, crustaceans, and octopi, yes, but not tetrapods. The kind of environment needed for some proto-fish to begin evolving legs simply doesn't exist on your planet.

Spoiler: long near-irrelevant digression on sleep patterns

Show

Sleep cycles evolved as a natural consequence of day/night cycles. If they evolved without day and night, any life form complex enough to require something akin to sleep would do it in another manner.

So let's look at alternate sleep cycles found in nature.

Fish apparently don't "sleep" in the same way mammals do, but do rest in place. They tend to seek out relatively secure places (rock crevices, large schools, or just the sea floor), and remain aware of their surroundings. This can almost be likened to conventional D&D ideas about how elves "sleep".

Some species of ant apparently take one-minute power naps through the day and night, totally about 5-6 hours a day. They colony as a whole never sleeps though. Most insects tend to sleep for a few hours at a time, following a day/night (or night/day) cycle.

Crabs tend to be mostly nocturnal, sleeping through the day. It's not clearly understood what cycle deep sea crabs follow, as they never see daylight. Fiddler crabs, which tend to live in tidal shallows, are an exception. Their sleep patterns follow tides, rather than day/night cycles.

Octopi are known to both sleep and dream. (Due to the fact that we can't actually ask any of them, we only know about dreaming for sure with a very small number of animals.)

Frogs sleep. But not in the same way as mammals. Their sleep cycles vary by species, by generally depend on day/night cycles. They also incorporate aspects of fish-like 'sleep' and non-dreaming 'unconscious' sleep.

Finally, some animals hibernate/estviate in winter/summer. In a sufficiently extreme environment, a fantasy species might get all of its 'sleep' in this manner, being constantly awake and alert the rest of the time.

----

So, all life needs to "rest". Sleep as we understand it (and especially dreaming) seems to be a requirement only for life with complex brains. Past a certain level (amphibians?) Some of that sleep needs to be unconscious. Past a higher level than that (mammals and reptiles?), the sleep includes dreaming. The exact cycle varies, but almost always follows from an environmental trigger, whether that be light levels, tides, or winds that change in a regular cycle.

[D&D_Fan]

Okay, let's assume the planet has an Earth-like atmosphere that distributes temperature such that the front of the planet isn't as inhospitable and the back side of the planet isn't as inhospitable. Wind and air are essential, heating and cooling cycles, rain, even the dark side is livable, it could even be comfortable in the right planetary conditions.

If there's an orbiting moon, time is based off of that. If the constellations change, the time is based off of that. If the planet orbits the sun, there will be time based on that. If an alien civilization brings their own timepieces, then those can be used too.

If neither are true, then it's always possible that time can be based off of movement and travel. One day? You mean how long it takes to walk 20 miles? It's a silly measurement to us, but at least it's mostly practical.

Biological clocks still exist as well, as many people have said, animals mature at rates and times, so they know when to mate and migrate.

All I know is that it would be very different from earth.

[Ashtagon]

If neither are true, then it's always possible that time can be based off of movement and travel. One day? You mean how long it takes to walk 20 miles? It's a silly measurement to us, but at least it's mostly practical.

A mile is traditionally defined as eight times the distance a farmer can plough in one morning (ie eight furlongs). Which makes your 'day' definition somewhat circular.

[D&D_Fan]

A mile is traditionally defined as eight times the distance a farmer can plough in one morning (ie eight furlongs). Which makes your 'day' definition somewhat circular.

Just imagine it in reverse, if the day was defined by the distance plowed, not the distance plowed by the day.

[Ashtagon]

So... "A 'day' is the time it takes to plough the distance between A and B."

Ron is strong. Ron's day is shorter than Wayne the weak.

I suppose that works about as well as the traditional units of length based on the body, albeit with a different set of arguments developing.

I'm still curious how these guys are gonna evolve legs with no tides in prehistoric times.

[Aotrs Commander]

So... "A 'day' is the time it takes to plough the distance between A and B."

Ron is strong. Ron's day is shorter than Wayne the weak.

I suppose that works about as well as the traditional units of length based on the body, albeit with a different set of arguments developing.

I'm still curious how these guys are gonna evolve legs with no tides in prehistoric times.

I imagine the same way as the arthropods did, a long time before there was any life on land. I'm not terribly sure I buy the arguement that amphibans only moved onto land solely because of tides (as I have never heard that theory posited until now) when there are a lot of other plausible reasons - like exploiting a new environmental niche (and there are no tides in fresh water, for another point); but even if so, a completely different roll of the dice might mean that there are not vertebrate fish in the terrestrial sense (or if they are, they may not be what moved onto land) and the land dwellers came from a different "vertebrate" group which evolved from something that, I dunno, started in the trilobite mould/niche (or sea-scorpion or...)

[Ashtagon]

The process is something like this...

Fish live in coastal waters.

Some of those fish explore waters that happen to be tidal. Perhaps the tidal waters are where land-dwelling plant life (food!) happens to live, accessible to fish at high tide but generally inaccessible at low tide.

They get caught out by a low tide and stranded on tidal sands.

Some of these stranded fish suffocate and die. Others figure out that by flopping around on their fins and writhing in a particular way, they can make it back to water.

The fish that happen to be able to flop back to water have an advantage over the ones that can't, as they can continue feeding in the tidal waters for longer. This means they can go forth and multiply more easily.

Random evolution means some of these "flopper fish" develop stronger fins; others develop weaker fins. The weaker-finned ones give up on flopping onto the tidal sands (or die, like the regular fish that get caught). The stronger-finned flopper-fish thrive even more, as their stronger fins enable them to flop around on the tidal sands more effectively.

Over time, these stronger-finned flopper-fish develop their fins into something resembling actual legs.

Without a moon, you don't get tides, you don't get tidal waters, and you don't get fish trapped on tidal sands, so this entire sequence of events can't happen.

(Yes, I know there are solar tides too. But that relies on planetary rotation, and this planet is in an orbit and rotation that is functionally tide-locked as far as solar tides are concerned.)

Loosely related: https://www.youtube.com/watch?v=M6_7Q7uUhmU

[Lord Torath]

But there is a moon, even if it's only been around for a few million years.

AORTS Commander, is that a few million "Earth" years, or a few million "Andorlaine" years? Because a few million Andorlaine years is a few billion Earth years.

[Aotrs Commander]

The process is something like this...

Fish live in coastal waters.

Some of those fish explore waters that happen to be tidal. Perhaps the tidal waters are where land-dwelling plant life (food!) happens to live, accessible to fish at high tide but generally inaccessible at low tide.

They get caught out by a low tide and stranded on tidal sands.

Some of these stranded fish suffocate and die. Others figure out that by flopping around on their fins and writhing in a particular way, they can make it back to water.

The fish that happen to be able to flop back to water have an advantage over the ones that can't, as they can continue feeding in the tidal waters for longer. This means they can go forth and multiply more easily.

Random evolution means some of these "flopper fish" develop stronger fins; others develop weaker fins. The weaker-finned ones give up on flopping onto the tidal sands (or die, like the regular fish that get caught). The stronger-finned flopper-fish thrive even more, as their stronger fins enable them to flop around on the tidal sands more effectively.

Over time, these stronger-finned flopper-fish develop their fins into something resembling actual legs.

Without a moon, you don't get tides, you don't get tidal waters, and you don't get fish trapped on tidal sands, so this entire sequence of events can't happen.

Having googled around the subject, there does appear to be a suggestions that tetrapods may have formed in tidal areas (OR areas of shallow fresh water) but, like, otherwise, no, that's... Not remotely what those studies are suggesting. Far more credibly, it is suggested that forcing through shallow water plant growth (e.g. mangrove swamps) may have been a contributing factor.

(We don't know NEARLY enough about early tetrapod evolution to be able to say "if not for this one factor" - and that in general, there is very rarely any one single cause for stuff in natural history anyway.)

What this would only mostly suggest though, is that any "vertebrate" "fish" are less likely to have evolved in to "vertebrate" "amphibians" and that the role of larger land creatures may belong to a more diverse number of kingdoms that evolved from more arthropodic-like stock. So it's a point to consider, certainly, but its by no means a "legs can't happen without tides."

(But it's also worth remembering that, at the end of the day evolution is ultimately a bit of a gamle); adaptions have a CHANCE of happening - and the first mutant has to survive long enough to reproduce (and the mutation has to be one dominant enough to be passed on); the chances come up because there's so many rolls of the dice, but sometimes, not even rolling all the dice guarentees a result. Conversely, sometimes nature rolls a few natural 20s in a row. A freak storm tosses something thousands of miles from where it lives an it survives and florishes.

Loosely related: https://www.youtube.com/watch?v=M6_7Q7uUhmU

Mu understanding was already that tetrapods have basically because that's what it turned out early on (why, we simply don't yet know), as and the video says, once you're lost 'em, you don't get 'em back.

(Thus, for example, to skip to another world and another alien species, the elenthnars, which have four "spider-ish" like legs and an upright torso with arms with four fingers and two opposable thumbs (because they came from arborial, not cursorial stock) indicate that the kingdom to which the E'len'deth'nacri (to use the scientific name) come from would likewise have been one whose hexapods developed and retained a six-digit pattern.)

But there is a moon, even if it's only been around for a few million years.

AORTS Commander, is that a few million "Earth" years, or a few million "Andorlaine" years? Because a few million Andorlaine years is a few billion Earth years.

Earth-standard years. Given the high orbit speed, it won't be stable in the orbit for many millions of years.

[Palanan]

Originally Posted by Ashtagon
The process is something like this...

As someone who’s both published on vertebrate evolution and who knows a thing or two about coastal environments, the “process” is nothing like that. I’ve never heard this claim before, and without going through every line of this post, I’ll just say that none of it is supported by any actual science we have. A red flag for me is the casual mention that these supposed fish “figure out” how to move on their fins. No one versed in evolutionary biology would phrase a major transition like this.

A recent paper from Byrne et al. suggests that tidal variation may have been one of several factors influencing vertebrate colonization of land, but at best this is correlation, hardly causation. They rather grandly describe their approach as “a field holding great promise” which is “still very much in its infancy.” That’s a long way from demonstrating any actual evolutionary effect, much less proving that tides are the cause of vertebrate expansion into terrestrial environments.

It’s also worth noting that tidal variation is only one of a number of ways in which fish can be brought into the land/water interface. River deltas, land subsidence, wind-driven waves, and seiches can all serve to populate an intertidal region on different timescales. And there’s no reason to assume that a direct marine-to-land transition is necessary, or the only possible avenue, when marine-to-freshwater-to-land is just as likely if not more so. As just one possibility, if anadromous fish evolved early on, that behavior could put them in a similar situation to Bryne et al.’s putative tide pools, but in a purely freshwater environment, without the need for actual tides.

So there are plenty of ways that vertebrates, or vertebrate analogues, could evolve on Andorlaine without requiring Earth-equivalent tides.

[Lord Torath]

And Andorlaine does have Earth-like tides. I did the math a page or so ago, showing that the tides the moon exerts on Andorlaine are the same as Luna exerts on the Earth. They last six times as long on Andorlaine, and lack the component the Sun gives our tides (which I understand is about a 10th as strong as Luna's tidal effect), so Andorlaine still has a variable land/sea interface. Of course, it's only had that for a few million years, and will only keep it for a few million more, but it does have tides.

[Palanan]

Yes, I did see that Andorlaine currently has Earth-approximate tides, but I’m assuming that the ancestry of its vertebrate-equivalents reaches back hundreds of millions of years, long before its current moon arrived.

It’s also occurred to me that a regular seiche in a large lake or small ocean basin could mimic tides under certain circumstances, and might be frequent enough to serve for approximate timekeeping. How that interacts with the current tide regime is up to the OP.

[Ashtagon]

No one versed in evolutionary biology would phrase a major transition like this.

Let's just say that were I writing an academic article or a university paper where I would be expected to cite references and annotate everything, I would have phrased it differently.

This is an internet forum for gamers, not a symposium of professors. I write to my audience.

[Aotrs Commander]

For the record, while I am not an Actual Paleotologist as Palanan is (which is dead cool, by the way), but I a very keenly interested layperson; what started with dinosaurs quickly spiralled out at a young age with a book by Michel J Benton which covered in brief the whole history and that bored right into my hindbrain (along with my first exposure much later to Anomalocaris, which remains my favourite animal). (Hell, part OF doing an entirely alien world is to apply the theory. I never create an aliens without asking "how did they evolve?") So I would consider myself to know enough, as they say, to at least edge of out of the other side of Knowing Just Enough To Be Dangerous. I think Ashtagon, you were writing down more than necessary, especially when you were replying to me specifically, as it made you sound to me like you understood it far less than I do. (I mean, I went and learned to do astrophysics maths for this, I would hope from context that would have at least suggested I can cope with at least the highest grade of popular science, if not bottom-end technical.)

[Palanan]

Originally Posted by Aotrs Commander
For the record, while I am not an Actual Paleotologist as Palanan….

Not a paleontologist sensu stricto, but there’s some overlap.

Originally Posted by Aotrs Commander
…Anomalocaris, which remains my favourite animal….

And fine taste you have indeed.

Originally Posted by Aotrs Commander
…I never create an aliens without asking "how did they evolve?"

Speaking of which, do you have a definitive list of the sapients which evolved on Andorlaine? I have a vague impression from this and previous threads, but I can’t recall if you’ve ever presented the full spectrum of species available as PCs for this world.

[Aotrs Commander]

Speaking of which, do you have a definitive list of the sapients which evolved on Andorlaine? I have a vague impression from this and previous threads, but I can’t recall if you’ve ever presented the full spectrum of species available as PCs for this world.

None, currently. There is the implication from the ghost-ship-city of the "ghost jellies" the Aotrs party briefly explored that there are probably humanoids(or something close) of roughly humanoid proportions, but basically thus far the only "on-screen" and coherent creatures are the "ghost-jellies" (seen as corpes as then as, like, ghosts...) and the rib-cage of a "demon brain." (Oh, as some vaguely shark-like EM insubstantial creatures from the Dark Side.) But that's it so far. The paleolithic tribe under consideration would be ostensibly the first.

Though if it wasn't already clear, the assumption will be multiple sophont species (of disprate morphologies) like a more traditional fantasy planet, rather than a monospecies-type set-up.

(With 2023 being what it is, work aside, my time is being completed with by three seperate projects - this, setting up my even-longer-desried non-egyptian mega-campaign (and trying to fit Desert of Desolation onto Golarion, which is harder than I expected geopgraphically...) and my major job convering over all my BattleTech record sheets (for about 400 mech models, of which there are an average of five variants per model...) from one outdated piece of software to a new one. So it's all slow going.)

[DavidSh]

A mile is traditionally defined as eight times the distance a farmer can plough in one morning (ie eight furlongs). Which makes your 'day' definition somewhat circular.

I had thought it went back to Roman times, as a thousand paces (mille passus). Or is that just a mad coincidence. I know my walking cadence at about 100 steps (50 paces) a minute gives me about three miles an hour.

[Ashtagon]

I had thought it went back to Roman times, as a thousand paces (mille passus). Or is that just a mad coincidence. I know my walking cadence at about 100 steps (50 paces) a minute gives me about three miles an hour.

It's complicated. There are many units that have been called a mile, and they vary quite considerably in length. The longest "mile", the Norwegian mil, was more than twice twice the modern international mile (most Scandinavian countries these days use "mil" to mean exactly 10 km). The Roman mile (at about 1480 m) is in fact the shortest unit traditionally referred to as a "mile" (or an etymological descendant of that "mille passus").

The English furlong ("furrow-length") was defined as I noted. That it approximates the Greek/Roman stadion/stadia is coincidence rather than intent.

The English word "mile" does indeed ultimately come from Latin. But the Roman definition of 1000 paces isn't exactly convenient. In a pre-literate age, counting that high requires a lot of concentration on the numbers, as well as concentration on maintaining a steady pace (ie marching). This was outside most peoples normal daily lives. What was within most peoples normal daily lives was farming. So it was natural to find a number of furrow-lengths that would approximate the older unit, in order to continue to make sense of the existing milestone markers that would have remained in place along the old Roman roads long after the empire itself had fallen.

In other words, they took the existing word, and redefined it in terms of units that they were using on a regular basis. Kind of like how in modern times we took the existing mile, and redefined it as an exact number of metres, replacing the traditional definitions then in use.