How do you tell time on a world with 9-year days?

Question

On my world, the day lasts 9 years: 4.5 years of light, followed by 4.5 years of dark. The inhabitants of this world survive by migrating along the ring of dusk and dawn.

How do these people tell time? Obviously the good old standard of counting day and night will not work, nor will ancient methods such as time sticks or sun dials. In a world where the days last years, how can a civilization accurately tell time?

Edit

The tech level I am interested in is the early medieval era, as after discovering a basic method, more complex ones would arise building off of that.

To Separatrix, the reason it would be hard is that to the inhabitants, it is always day, they simply migrate around the planet to remain in the day side as the night side is certain death.

As frarugi87 pointed out, I forgot to mention; this planet has multiple small moons that orbit it as well as a small ring.

Answer 1

Terrain objects

I imagine these nomads are following the same paths every year as they perpetually circle the planet. In that case, since there are no seasons or months, each group's time cycle would be based around terrain objects they pass. This is the month of the Blue Woods, next month is the Snow-capped Peaks, next month is Dust Plains, etc.

Once your people evolve past the small clans stage (which I'm not sure if they have) and start having more trade and contacts with other tribes, I'm sure the groups would adopt or impose calendars from one another. For example, the peoples of the Iranian and Anatolian plateau picked up the Babylonian lunar calendar through trade contacts, while the Julian calendar was stamped onto most of Europe and the Middle East through conquest. At that point, the 'winning' time system would be that of the most powerful or culturally advanced groups.

Answer 2

For Months/Seasons:

The terrain. Presumably they will be in the same place every nine years, and they know where they are relative to the cycle. You'd get the Month of the Great Salt Lake and so forth. This would divide your "years" into "months"

For Days/Hours:

Water Clocks or Hourglasses. Even on a moving cart (I'm not sure how fast the people are moving or how long they stay put) these would work reasonably well. Additionally, as nomads, they are sure to have flocks of some sort as agriculture would be difficult. As such, they would know about how long an animal can go before it needs to eat or sleep. This would divide the "days" into "hours" You'd end up with the Hour of the Horse and the Hour of the Sheep. You'd also know how long the by products of any animal lasts. That would divide the months into "days"

Basically:

You'd end up with people that sleep when the horses sleep, move camp twice for every calving, and breed your sheep each time you leave the mountains or forests. Cycles upon cycles using nature to time the gradual migration around the planet. And as a result, those cycles will get named after the nature that counts them out.

Answer 3

Does/can the planet have a moon? If it had several small fast moons like Mars, then that's a perfect external reference point.

For instance, Phobos has an 8 hour orbit, and Deimos has a 30 hour orbit.
So on the 9 year planet one orbit of Moon 1 is one time unit (say an hour), and an orbit of Moon 2 is a Day. Or whatever. It would be a little like the hands of a clock, depending on which moons are in the sky and where.

Edit:
If not a moon, you want something that can be seen during the day. This means that using the position of stars/planets is out.
One thing that will be visible during the day is the primary star (hereafter called the sun). The sun will be visible from anywhere on the daylight side of the planet. It will have it's own rotation, and one thing that would be visible (with proper light filtering equipment) would be sun spots.

If you were able to pick them out against the glare, possibily using something like a pinhole camera, you could determine the speed of the suns rotation, and from that measure the passage of time pretty accurately.

Answer 4

What about the change in the length of a mans shadow? After migration is completed the length a typical mans shadow is 'x'. When it's time to migrate again, the shadow of a typical man is 15*x.

This is pretty simple if the planet is relatively flat. Mountains, trees, fog, clouds, rain, hills, could make it kind of difficult.

A "clock tower" (a large pole, whose height is fixed & shadow is measured by a rope) could be erected every migration. After 9 years, you may just migrate from clock tower to clock tower. A clock watcher could ring a bell every time the shadow changes it's length by a foot, or what ever is suitable to divide up a eat/work/sleep cycle.

"Come on over for dinner in 3 migrations & 40 shadows", could be the earthly equivalent of "come over for dinner in 6 weeks, 3 days, & 16 hours".

Of course this all hinges on the assumption that the people can migrate faster than the livable zone moves, allowing them to 'settle down' for some significant period of time.

Answer 5

By using a thermometer!

Assume your world has a size similar to Earth ( 40.075 km) to do a roundtrip around equator, you will need roughly (assuming a walking speed of 6 km/h and you spend 1/3 of your life walking):

$$40.075 \cdot \frac{3}{6} = 20.000 \text{ hours}$$

Nine Years have 78840 hours, so the scenario holds from timing point of view.

However a so slow rotation will cause the Earth to have 1 hot side, and 1 cold side ( 3.200 times slower than Earth).

This will cause a very static weather, we have 1 cold air current going from cold side to hot side at ground level. and 1 hot current at higher level going from hot side to cold side.

Basically there will be a constant cold wind at ground level. The dawn zone will be probably too cold for living, so people have to stay within the "early morning zone"

Basically when it starts to get too cold, it's time to move on, and when it starts to become too hot, then its time to settle. And the best time measuring device (since the wind will be constant) is a thermometer. People could live in the 10-27C° zone in example.

In reality I think this scenario will not hold, you do not have the time to grow and harvest regular vegetables (At least 3 months as far as I know are required for shortest living crops, and note that his crops use help from chemical industry).

You need also fictionary vegetables able to grow in 1/2 months.

The crop growth could also be an alternative measure for time. Basically people should harvest the crop, then start moving immediatly until it finds a zone suitable for seeding again.

I'm not a meteorologist, but I think that there will be zone with constant rain, so basically people have to "travel" through rain, wait that rain come, harvest crops, then leave again.. living on the edge of rain!

Answer 6

Let's suppose they are ordinary humans with ordinary needs for meals and rest.

Perhaps the lack of day/night cycle would actually create societies where everyone works and rests at different times so the group is always active, always alert to predators and other clans. People would eat when hungry, sleep when tired, and everyone would have their own schedule.

In this case timekeeping would actually be quite important to help people with different schedules co-ordinate. Perhaps bells would be sounded every hour or two (say) as a means of marking time.

But how long is "an hour or two"? Well, the time does not need to be exact. One possibility is a traditional unbroken song is sung by the religious order (with individuals joining and leaving the song to eat, rest etc.) and at particular points in the (long) song, the bell is struck.

Alternatively the constant migration might lead to a religious practice where a group is constantly marching, perhaps in a large circle, at a slow and very steady pace. Every thousand (say) paces the bell is struck.

That said, it is quite complex for everyone to be working to their own rhythm, especially in simple societies. To create a more orderly approach, there could be a bell sounded every 12 hours, with people "swapping over" from work to leisure and rest and vice versa. Or there could be 3 "phases" in everyone's day (basically work, leisure/socialising, sleep), each of around 8 hours, with 3 different cohorts doing different things at different times.

How would such long time periods be marked out? Consider a pyramid of 25 stones, that is to be moved by 1km, one stone at a time, in a process which takes around 8 hours. To keep time reasonably well, the site could be chosen 1000 paces from the old one, and the aim would be to complete it just as sunrise/sunset hits the new site.

Answer 7

Here the astronomical methods:

Long timespans:

In the night zone the sky is an excellent calendar because it slowly and uniformly rotates. Expect the inhabitants to divide it in areas like the Chinese zodiac and name them. Your world may contain fast-moving stars like Barnard's Star where the movement will be noticed over long time-periods and used as indicator. If your planet has notable precession, tilt and eccentricity, very long timespans will result like the Milankovitch cycles on Earth in ice ages and warm intervals.

Shorter timespans:

Both at day and night planets and moons (perhaps even the ring) is visible. The ring may contain shepherd's moons which apart from their visibility will cause noticable wakes in the ring. There are some formulas which allow you to calculate the duration of a cycle for a moon, which can range from hours to months. Other bright planets may be visible in weak daylight and astronomical instruments may see moons orbiting those planets. Jupiter's moons were in fact used as extremely precise clocks to calculate the longitude of a location on Earth (This does only work on land; on water even calm sea does not allow such observations).

People may have precise angle measurement devices like the nocturnal to measure the angle between two positions of celestial bodies to get a more accurate time span. Other devices are hourglass and water thiefs. In the early medieval era big mechanical pendulum clocks are possible, but expect them to be extremely expensive and therefore only used by extremely rich people.

Tides
Your moons may cause noticable tides on the planet, so even if the sky is not visible, the current flow of water on the coast may give your inhabitants an approximate timeframe.

Animals
Given that the day is extremely long, most animals will also wander around the planet. Like the dawn chorus of birds people may know by the acoustical environment how the habitable zone moves and therefore how much time has elapsed if they did not move.

Very short timeframes.
Interestingly the Jewish people use rega (moment, plural: regaim) as subpart of a chelek which is approximately 1/20th of a second which is in fact very near to the shortest discernable timespan; magicians know that actions lasting shorter than 1/20th of a second cannot be perceived. So you might use some timespan to accurately describe fast actions.

Answer 8

They may not use time

The concept of time is mostly European (1), and some different cultures don't value time much, or even have no concept of it. (it's often the case in nomadic cultures.)

That can work, as they could have a non time structured society, where when someone is available to work, they do, and when they aren't (sleepy,hungry etc...) they do what they need.

Most cooking can be done without time "when the meat is brown" "when the dough doesn't stick"

This could be an interesting clash (if they ever encounter each other), where sunset or dawn dwellers could have almost no concept of time, "well, when it is too cold/hot/dark/sunny, we move" and the other ones are really extreme on time "if you are late you are executed."

and even if there is no encounter, as I assume your story will be in an European language, and a species almost without time will clash with the reader's culture, giving them an "alien" feeling.

(1) I include today's Canada/USA and Asia (and some other countries) as they are influenced by the European culture.

Source : http://www.andersoninstitute.com/cultural-perceptions-of-time.html

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note: this answer does not replace other ones, as they are good reasons to keep time in an advanced civilization, but it is an option.

Answer 9

TL;DR They would use basic physics-derived methods of telling smaller intervals of time, time required to do things (like build a camp, hunt, walk somewhere) as larger intervals, and arrange those intervals as denominations of the time that it took for the twighlight zone they live in to fade to night - which would essentially be a season.

On an earth-like planet with this rotational time, that season could be 2-4 months assuming the people travel until they reach sunset, longer if they move further into the day side.

Example; it takes quarter of this time to build a good camp, a big fire takes the same time to burn down as it does to hunt something, a puddle evaporating in sunny weather, etc.

I think with these limitations, telling the time precisely would be impractical for them unless it's in small intervals or arranged around when they are hungry / sleepy (which would still be imprecise).

Maybe hourglasses would be invented for smaller intervals. Sundials wouldn't be very useful since the sun would perpetually be setting, i.e it wouldn't move across the sky at all.

Longer Explanation

According to some maths* I did which assume an earth-like planet, the "fade" zone or twighlight zone (i.e the rotation of the planet) would move at roughly 0.5 KPH (circumference of earth divided by number of hours in 9 years).

If the twighlight that the people live in is similar to earth's, you have about the time it takes the center of the sun to reach 12 degrees below the horizon in which to do things using natural light - after that it gets too dark. i.e "Civil twighlight".

The planet rotates at around 0.004 degrees per hour (360 divided by 78840), meaning to rotate 6 degrees would take 1500 hours / 62.5 days.

So, very roughly, the twighlight would last around 2-4 months (from sunset), which isn't too large a time for people to notice that it's fairly consistent, and during this time the sun would noticeably change position.

Looking at it this way, if one were to tell the "time" by phases of the moon on Earth, it would be quite similar, with the added circumstances of having to pack up and move home every time it waned.

This would be the foremost basis for them to create a calendar system since it's central to their survival - further denominations of this would be measured by how far the sun had set, whether stars could be seen, or some of the moons perhaps, but I think being able to say "it's 4pm" is way too precise for a world like this.

planet assumed to be earth-like, numbers rough and guesstimates made, there are 365 days in every year. maths is not my strong suit.

Answer 10

I believe the only active biology would be in the dawn zone. Plant life would have to be very robust to survive the cold of the night and the heat of the day. It would probably shut down in the extremes. So animals would also need to hibernate at night and estivate most of the day. All feeding, breeding etc would happen mid-morning. On the dusk side it would be long after dark before it was cool enough to do anything so the plants would be inactive anyway.

So the traveling humans would be hunter/gatherers living in a perpetual spring harvest. Anything which prevented movement would be extremely traumatic: illness, giving birth. No endeavor requiring a person to be static for more than a few days could ever be done. You would need to work out exactly how long it was possible to remain still. There would be a 'fundamental duration' based on walking right to the edge of the dawn zone and staying there until it got too hot to live. How long? I'm thinking maybe a month. Most likely there would be 'cities' every hundred miles or so with fast roads between. Each city would be visited for a 'month' every nine years.

Perhaps life would be 5 'days' of walking followed by 25 'days' of city life on a perpetual cycle. Any criminals to be executed would simply be left behind in a cell and would boil to death a few days after the city was abandoned.

There would be a tendency to push away from the equator, ie to invade your northern or southern neighbors, just to have less walking to do. States/counties would be banded on latitude.

Close to the poles there may be permanent settlements where the residents just endure the extremes rather than migrating. Their tech level would be much higher. However food would not be plentiful so they might do a lot of trading tech for food with the equatorial nations. Imagine how popular a bicycle exporter would be.

Answer 11

Measuring the progression of time would likely be similar to the ways we do it or did it throughout history. Sand timers, burning candles, swinging pendulums would basically still be used to count out reasonable durations of time.

But I think you are asking more about how can they tell what part of the day or year are they in. That information is closely linked to navigation as well. How do they navigate? One important question to answer is what is the axial tilt of their planet.

Constellations would be a very important factor. If they follow dawn/dusk around the planet, only certain constellations will be visible at any particular time, and only the brighter stars will be visible if the sky isn't black. They will also teeter left and right (like a swinging pendulum) with a period of one of their years. This would depend on their latitude as well. So telling time and knowing where they are on the planet go hand-in-hand, just they do here on Earth.

They might also learn to recognize certain warning stars. Once a certain star becomes visible then the sky is getting too dark and it is time to move farther West or East for example.

Presumably, being in the daylit side could get excruciatingly hot. I expect they would stay in a zone where the sun is a certain height (angle) above the horizon. The position of the sun would be a very good indication of the relationship between their position and the time of day or year. If they stay close to the planet's equator they will likely have to move much more rapidly than if they inhabited zones nearer the poles.

Realize that on Earth, sailors at sea can only tell time by the sky if they know what their latitude/longitude is. Hence the concept of timezones.

Since you say that your planet will have a ring system, it will be very easy to tell what latitude you are at by the appearance of the rings. Maybe the nomads, while migrating, try to keep the rings at a more or less constant angle. And maybe living within the shadow of the rings is how they keep from scorching in the constant daylight.

Answer 12

Very interesting idea. If they are chasing the dark side, what would they eat? Wouldn't the lands ahead of them always be wastes? If they were instead running away from the darkness, they would have food on the sun side, potentially. Though that might also be a blighted waste.

As far as time goes, they could put markers down and measure the time at each marker. A marker for each year, and maybe some sub-increments under that. They could have holy sites dedicated to the markers, worshipping different gods or aspects of nature depending on what is around. I will say, though, that time tends to be something used primarily by folks who are settled and industrious. These people sound like they would be moving so much that time-tracking would something they wouldn't necessarily need. They don't need to get up at any particular time, just keep moving away or toward the darkness. They don't need to be home or eat at a certain time, because their sleep cycles are probably just as needed. They also wouldn't have a circadian rhythm because they have no day/night, so you may want to think about how that would affect their way of life. Ensure they don't have anything based on circadian rhythms. Which largely means they wouldn't really need or want to schedule much.

Answer 13

tl;dr They will use a combination biological factors, rest cycles, and outer space to determine time to an accuracy that they need in their daily lives

They are nomads. They are going to be following behind dawn just long enough for the lands to have thawed and grown food to scavenge, but not long enough for things to start to burn. A goldilocks zone, more or less. Essentially, they will live their entire lives at (what we would consider) the same time of day.

To answer the question, you have to ask yourself what exactly is accurate time to these people? We have time scales of seconds, minutes, hours, days, weeks, months, seasons, and years. Which of these need to be accurate? How accurate do you need them to be?

Seconds and minutes are useful when mainly at really short scales. A second is a heartbeat long. You might use this timescale for several thousand seconds, but not for longer than that. It doesn't makes much sense to keep count of 50 million seconds. 'Wait 50 beats then come and get me' makes sense. 'Plant these seeds, then count to 50 million' makes much less sense. This is true for us and them. It is only well past the middle ages that we had anything accurate for keeping accurate track of seconds over long scales.

Human hunter-gatherers wake up on first light, spend the day hunting and gathering, then when it gets dark, they relax for a bit, then go to sleep. They have no need or any real conception of keeping the time of day outside of morning, afternoon, evening, night. Their hours are are lot less accurate than our are, mainly because they have no need for more accuracy. Your medieval peasant didn't have a sundial. They knew when it was the midday sun, dusk, etc.

This would largely be true of people on your world also. While human sleep cycles depend on the sun, any creature from your world would have evolved a different mechanism to control how long they are awake for and how long they sleep for, but they would still wake up, slowly get tired, go to bed. You might have the circadian rhythm determined by pheromones so that any tribe/social animals sync up sleep times to their 'Alpha' or 'Queen'.

One possibility: The queen releases some pheremones upon waking. Everyone around her gets a buzz that slowly depletes throughout the day. Each member of the tribe will be able to feel exactly what time of the day it is, depending on how 'high' they are.

Whatever you decide to do, there has to be some sort of biological mechanism to the circadian rhythm.

Obviously, days are sleeps. I might make sense for your people to keep track of number of sleeps (days) and group them into units (weeks or months). I really depends on their culture.

Seasons and years will depend on your planet's seasons. If it has a winter and fall cycle, the people will probably want to keep track of that. This is easy, however because it is all determined by astronomy. Where the constellations are, how high in the sky the sun is, etc.

Answer 14

The time telling through sundials and other means would be the same. A species living on your planet wouldn't look at 1 day as being 9 years.... it would be 1 day to them. If you are asking about how would a human from earth tell time, they would either still choose to use earth time constructs so that they don't lose themselves relative to earth or they are adapting to the new world. Either way, telling time would be no different from earth or this planet. The only difference is where is the perception of time coming from?

Also things on this planet would more than likely age differently. Our age and time scale is based around our 24 hour cycle. Whose to say that a species on your planet doesn't live just as long there but 100s of years old to us due to what ever factors that may make them live long there.

Answer 15

As we are talking Medieval level of technology, I assume you need time for keeping calendars, as timekeeping on the scale of hours/minutes could be easily done using clepsydrae.

Also, I understand you mean "solar day" lasts ~9 years, not "rotation period", i.e. time planet rotates around its axis (See wikipedia article on Venus for the example of extreme difference between two).

Now, because of this peculiar geography I assume you have a need to know the time of "rotational day" for calendars and historical records. Achieving this would be relatively easy if planet has magnetic field with magnetic poles not coinciding with geographical poles, as the angle between magnetic north and true north will depend on geographical location. As your people move with solar day, the year for them will end when magnetic pole will point to true north.

Answer 16

I can imagine time measurement by using reusable items like hourglass, hour candles might be to much efford to reproduce, beginning with finding your resources on your 9 year trip around the planet.

But how come they even found hourglasses? This all beginns in a safe harbour, a home, a world just like we know it.

Societey has to arise. Humans coming together in packs start specialising in theyr tasks. They build shelters, not everyone will be on the hunt or searching for food in an ever new place.

This won't work in a society that stared with a 9 Year-long days, which forces them to be on the run theyr entire live. Those humans would just live by what has grown over last day or even more in case they don't walk the perfect circle and miss places they had been beore, guess it's hard to be sure you visited this exact same place yesterday/9 years ago and you only walk in one direction, maybe you don't even come up with the idea you came back on the place you have started! They probably won't start building housings in any way since they would have to leave it faster then they can make theyr mind of how to build a well constructed long-time-home. The few who did this way felt comfortable started to learn about planting food and ... died when they had to learn this does not work at night.

Actually id say those who don't develop the instinct to keep on running become extinct. This way there is no save harbour to make some random experience about tools, making fire, grow food. And try to carry arround your rectangular stone while inventing the wheel, this would be to much a burden.

So this needs a safe harbour i sayed, but where should this be? Well, right there! Make the world slow down in rotation (not that hard people start falling off your planet by negative acceleration). How settled this world is before the happening and after is up to you. You are also up to how long this happening lies in past. Technical progress might had slowed down since people don't come together like they sued to to share theyr knowledge. Also people have no time to spend on learning, they have to gather food in the new place they reach in theyr travel cycles, prepare for the travel in the next "day" or hourglass run. The hourglass will be kept by an elder time-keeper or a chief. This person is the metronome of a group tribe, like church bells used to be in some places.

Citys once beeing all over the planet had wearn away, ruins under piles of dirt are relics those new people can't remember anymore. They lost a lot of technological knowledge and might not even know, how or when the magical time articaft was crafted, which had to been turned 10 times before they had to travel 4 times the relic.

tl;dr People measure time in a reusable way theyr technological advance allows them, like hour glases. People have been on the planet since forever, but the planet changed, it slowed down spinning thousnads of years ago and societeys dacyed. Who is left are those people who early enough started to travel and follow the sun. They have not have found any time to develop on new technologies or anything since theyr all-days destiny is to march every day, following the never setting sun.

following my OLD POST i made but was criticized, so i rewrote it, just did not wanted to miss a point.

I think this doe's not work since this entire Planet leaves no space to stay for long enough humans would evolve the way they did (depends on the planets sice) but imagine peope in the very first stadium like wild animals in a herd.

They would live by what has grown over last few years while they travled and what lives there when they appear. They probably won't start building housings in any way since they would have to leave it faster then they can make theyr mind of how to build a well constructed long-time-home. The few who did this way felt comfortable started to learn about planting food and died when they had to learn this does not work at night.

Actually id say those who don't develop the instinct to keep on running become extinct. This way there is no save harbour to make some random experience about tools, making fire, grow food. And try to carry arround your rectangular stone while inventing the wheel, this would be to much a burden.

As long as there is no safe harbour for your people to develop into this stadium there will be no evolution from herds to social structure we have. And without this, noone will be like: let's meet next weekend, i have some busy days, can't wait for friday.

So if you say you have this save harboud, people can develop a society, share theyr tasks and build up dependencies they can better organize with time. But then they would know night and this won't be the death side of the planet anymore.

EDIT: well about the safe harbour thing ... you might make your story up like: earth or whatever planet started to slow down rotation. This way you can have your setup developed they way you need including technologie and you could reason why people had a meaning for time like we have, even if it might be implausibel to native creatures on such a planet who allways lived with sun high over theyr heads.