You are native to a planet that falls between two suns, thus ensuring eternal sunshine.

How would we be able to tell the time? Do you formulate some kind of system based on which sun is in the sky at this moment?

What if your planet rotates at the same speed the suns orbit each other? making them appear to be frozen in time, as they will never move from their position in the sky.

I suppose we could always base time on some arbitrary measurement, such as how long it takes for water to drain out of a certain sized bucket, or better yet; the duration of your farts.

Is it even possible for this mortal race to never learn the concept of time? Growing old and dying is merely something that just happens, an act of god even?

Just curious as to what thoughts you may have. Sorry, I should have mentioned, I've been ignoring the physics of the situation I do believe this situation is most likely impossible, I've been coding a randomized planet gen. Ended up wondering about Eternal day, and here i am.

  • 2
    $\begingroup$ The concept of time is based on predictable change. If we didn't have a regular night/day cycle, maybe we would base it on the cycle of the tides changing. Maybe there's a creature that migrates twice a year we can base it on. Maybe time is defined in terms of reproduction, or even aging. Any regular, repeating, cycle can be used to quantify time. $\endgroup$
    – enpaul
    Sep 29, 2017 at 22:59
  • $\begingroup$ Aye, could also be based on a feeding cycle as well i guess $\endgroup$
    – ultorian
    Sep 29, 2017 at 23:07
  • $\begingroup$ If the planet move back and forth between 2 stars, the shadows in the valleys can be used... $\endgroup$
    – user6760
    Sep 30, 2017 at 3:26
  • $\begingroup$ what do you mean with "What if your planet rotates at the same speed the suns orbit each other?" $\endgroup$
    – L.Dutch
    Sep 30, 2017 at 3:36
  • $\begingroup$ @L.Dutch - Imagine a binary star with a planet located at the two stars' common center of mass. By the planet "rotating at the same speed as the suns orbit each other", ultorian is positing a situation where the planet's rotational period is the same as the stars' orbital period, which would cause the stars to appear stationary in the sky to an observer located on the planet. $\endgroup$ Sep 30, 2017 at 11:17

9 Answers 9


I cannot imagine a planet between two stars but this is my failing. They would need to be very far apart for the planet to be survivable.

I cannot imagine a planet between two stars in which both stars are equally intense. In most cases one would likely be notably more intense, and dominant. It may be bigger, pulling the planet towards itself.

The dominant star dictates the time of day, as it make the land brightest at 'morning' and less bright when it sets.

Lastly, there are many stars in our sky besides Sol but they are of very small intensity in comparison.

I apologise for the poor language in this response. Down vote if need be. But the premise seems ill considered. The stronger star dictates day, but the whole orbital geometry sound quite odd.


Is it even possible for this mortal race to never learn the concept of time?


People will only develop a concept of time if they need it. I have no source available, but I have heard of natives without a concept of time. They only live now, not in a timeline. A timeline is an abstraction we cannot see or touch.

On earth we have obvious cycles of day and night, the moon, and the seasons. Farmers are likely to develop an abstraction of a timeline. Hunters less likely. People living at places, where everything needed is available without long-time plans, don't need a timeline.

If there is a need for time measuring without seasons and sky events, there are some possibilities. Short times can be measured with heartbeats or breathes. A longer time period is a time-mile (= the time you need to walk a mile).

In Germany, an acre of land is a "Morgen" (= a "morning"). One acre is the amount of land you can get your farmer's work done at one morning. This is an example for the other way around: An amount of time to describe the size of an acre of land.


Our earth-based measurement systems all started out as very crude approximations. The foot was literally a foot. No need for standardized units, as precision was never necessary. You paid for what you got, and you got what you paid for, even if it was just 'estimation'. Basically, it was "I will pay x for that length of cloth, which looks approximately long enough for what I want'.

So i suspect time would be measured by a few parameters (like the difference between foot (your foot), a yard (distance of your arms), and paces (distance of your stride).

You would have a short time internal, for short periods of time - say, a heartbeat, a longer period of time, perhaps a circadian rhythm (natural sleep cycle), and maybe something gestational, like a female period.

The body seems to have a natural circadian rhythm independent of day-night cycles, that are relatively consistent even in caves where the light is kept constant. Biological clocks are amazingly accurate for anything other than science and wages.


A binary star system's stars spin around each other (or rather, orbit the center of mass of the system, which would be probably close to where the planet is - think of the religious implications!), and this would also cause the planet locked between them to rotate. So the star constellations around the planet would change over time. The zones close to the divide between the sunny and dark sides of the stars would probably be the most hospitable for life and this is also the place where the distant stars would be most visible if the thickness of the atmosphere allows for it. So they could base one of their units of time measurement on the rotation of the star constellations.


To first better describe this planets position from what you said:

It's essentially tidally locked between the pull of 2 stars so its not orbiting anything.

A sentient race under these conditions would likely never develop the same measures of times that we do (days & years).

However depending on their technological capacity it would be inevitable for them to come up with some way to quantify the moments of their lives. things like seconds minutes hours, but they wouldn't be same duration as ours simply because our duration of a second is completely arbitrary with respect to time in the physical laws. We derived its duration from our primitive measurement of the day which is completely subjective to our species.

But the bottom line, in order to have things like an understanding of physics or an economy there has to be some communal understanding of time.

like "my village is starving, I will pay you 50 gold if you can bring 100 bushels of food to us in 60 wonki-hrs" without the concept of time scheduling in that scenario trade breaks down and the villagers starve.

  • $\begingroup$ So the planet should stuck in L1 Lagrangian point between two stars. L1 is not a stable point, though. $\endgroup$
    – Alexander
    Sep 29, 2017 at 23:08
  • $\begingroup$ @ Alexander I think that's a problem for the OP, but the planet rotating as its stars do and no chance of night means that is where it is. $\endgroup$
    – anon
    Sep 29, 2017 at 23:12
  • $\begingroup$ @Alexander That may be correct, but it's largely outside of the scope of the question. Honestly, being in a binary system can be pretty irrelevant to the question of "How do you track time without celestial markers?" $\endgroup$
    – Andon
    Sep 29, 2017 at 23:14
  • $\begingroup$ you're absolutely right, for any kind of progress to be made, you do need a communal understanding of time. I realize this, still; I find it appealing to think outside our human experience, or even what logic might tell you. $\endgroup$
    – ultorian
    Sep 29, 2017 at 23:16
  • $\begingroup$ @ultorian That's what im trying to get at, whatever they come up with would be more arbitrary than our own day and virtually outside of the realm of reasonable human speculation. $\endgroup$
    – anon
    Sep 29, 2017 at 23:18

This question is very similar to this one

Physical processes could be used to measure the passage of time such as water or sand falling through a narrow channel, the amount of time it took to walk between fixed land marks, regular eruptions from geysers and regular animal behaviour such as hibernation or migration. Human and animal bodies also include a number of rough and ready embedded “clocks” such as heart beats, the circadian clock, female Oestrus and the growth of offspring to a particular height. Plant growth would also provide another mechanism.


Time is generally measured in units relative to a specific event. In our case, with the Gregorian calendar, it's rotations of our planet around the sun relative to when Jesus Christ was believed to have been born when the system was first conceived (in actuality that date is most likely 2-3 years off).

Any system of time would likely be based on a similarly major event. It could be the birth of a major religious or political leader, the believed date of creation, or the time of a catastrophic disaster. Here are a few examples:

  • The time of a religious or political leader being born or coming into power.
  • The date of a major natural disaster such as a volcano, asteroid impact, or flood.
  • The time that a major war began or ended.
  • The believed date of creation for the planet, as decreed by religious leaders.

Next, we need something countable that progresses as time passes. In order to be an effective measure of time, it needs a few qualities.

  • It must be widely known. In order for a system to be widely used, everyone must have access to that information.
  • It must be indisputable. This isn't strictly necessary in the short term, but a system will break down if it's not the case. There needs to be a clear hierarchy of who is correct, or a way to indisputably settle the matter.
  • It should be fairly regular and consistent. The closer the length of time is to something measurable, the better.

Here are some options and an evaluation of each based on those three categories.

  • The current ruling leader. Each time one dies and is replaced, that marks the most significant unit. Smaller units are up to the decree of that leader, and could be arbitrary or based on a natural regular event if one exists. All events can be ordered chronologically. So for example, you might say you are in the 53rd decree of Tiberius. Since each decree is unique and individually countable, there is no ambiguity.
  • If there was a large moon or other visible celestial body that moved regularly, that could be used to measure the passage of time. The use particularly of stars could work, if they were visible at regular intervals.
  • A natural process which takes a consistent amount of time. For example, the pouring of a standard quantity of sand or water through a standard size of hole. This is a more advanced system, since it requires sufficient technology to standardize the units of measure. Each town can keep their own standard timer (or more than one) and continual communication can act to synchronize the systems. It's important to note that there must be a hierarchy or system for handling disputes, since each clock inevitably will drift relative to one another.

Here are some others that I don't think are likely (and why):

  • Circadian rhythm. Firstly, the circadian rhythm is heavily driven by sunlight. If there is no sun, why is there a circadian rhythm? Secondly, of who? Who is officially keeping track of it? Even on Earth, with the sun, the circadian rhythms of people vary and can drift by a full hour each day. Think about how some people are early risers and others can party late into the night. What makes you think there would be a circadian rhythm, or that there would be any consistency at all between the circadian rhythms of people who don't even have a sun?
  • Regular eruption of geysers. This comes down to the same issue, with the possibility to become out of sync quite easily. Not everyone can see the geyser, and there's no way to distinguish one geyser event from another. So if one town gets the idea that it went off twice, through hearing of the old event from a second source, then they are now out of sync with everyone else. Such inconsistencies can easily develop over time, so this system would require a central authority to maintain the counter. And the unit of measure is now simply back to the decrees of that central authority.
  • The tides. This requires a moon or other large object that moves relative to the planet. It would work if you were a coastal town, however if you were not, then you would have no access to this information. Thus, such a system requires a central authority. So the real unit of measure is simply decrees of that central authority. Not to mention, if you have a visible moon, wouldn't it be easier just to track time based on it's visible position.
  • Hibernation or migration. These two systems are governed by changes in weather as a result of our rotation around the sun, so they would not apply to this star system. For example, bears hibernate or birds fly south in winter, but without winter there would be no need to hibernate or fly south.
  • Female reproductive cycle. Varies considerably between individuals, and thus this would inevitably not be synchronized. If you use the reproductive cycle of one person, this is back to the decrees of a central authority. And that's an odd choice for the central authority.
  • The growth cycle of particular plants or shrubs. This varies considerably from plant to plant, and it would be very hard to keep consistent. So again, you are back to the decree of a central authority.
  • The seasonal cycle of particular plants or shrubs. The general idea that plants start growing in spring, and can be harvested in the fall. However, without any variation in seasons, it's incredibly unlikely that plants on this star system would have the same seasonality. There would be nothing to stop a farmer growing crops in winter or fall or at any random time of year.

This situation has a very simple answer ( for my non-scientific mind).

Lunar option

Have in the planet's orbit a moon,and thus the civilization would develop a lunar calendar. Heck you could arrange the orbit so then every 12 earth hours it blocks out the light from one of the Stars in the system. If that kind of orbit would mess with the moon (which I doubt), have the moon in a polar orbit.

Axis option

Another plausible solution is to have the planet's axis tilted beyond the plane the the stars are on. This would make instead of night and day, a sort of dawn and dusk situation.


It is really tricky to not have a sense of time. Any predator or prey has an intimate understanding of time, because time is literally a matter of life and death. But is there another way?

Perhaps we can borrow from the computer world. Computer systems often treat time very differently. In your question you talk about a species that "never [learned] the concept of time." You used a definite article in that sentence: "the concept of time." As though there is only one. It turns out that time is actually quite complicated, and if you delve into the philosophy, you find there are many understandings of time. However, for this answer, I'm going to assume you refer to the continuous time that we use in equations of motion in science. It's the only one which is ubiquitous enough to earn that definite article.

It's also a meaning of time that computers tend to not have. When we design most algorithms, we simply don't have that concept of time. An algorithm runs as fast or slow as it needs to, and when it's done, it's done.

So how do computers react in a world which appears to be ruled by our concept of time? One of the main approaches is to use what are known as "interrupts." Basically, these are specialized signals which, when triggered, interrupt whatever processing was being done and force the processor to run another bit of code. For example, when you press a key, it sends an interrupt to the computer which basically says "a key got pressed. You should read which key is being pressed right now, because they're going to let go soon, and then no keys will be pressed for you to read."

Interrupts create an interesting pattern. They don't have the sense of time that we have, used in Newtonian calculus. What they have instead is a concept of causality and "happens before" relationships. Believe it or not, you can have the concept of causality without a sense of time as we know it. Instead, you just have a series of well ordered events.

What I like about this pattern is that said species is not immediately turned into chow by a predator that has a sense of time as we know it. This species could have interrupts set up in their mind such that when the predator acts, they react. They may be unaware of the time flowing, but they can memorize a set of reactions which keep them safe from a sabertooth tiger. It might even be very aggressive. They may have a trigger which tells them to jab the tiger in the eye. They could do this without a sense of time, so long as they didn't have to solve any calculus equations to predict where the tiger's eye is. Accordingly, they would live in an environment that permits this. They would live in an environment full of complex traps, such that once a tiger falls into a trap, it remains stationary long enough for the members of our species to figure out how to dispose of it without having to do any complicated timing.

What they would be very bad at is balancing acts. Without a sense of time, tasks like balancing a broomstick on their hand would be very very difficult. Bang-bang controllers, which are independent of the flow of time, are not very good at this task. However, they could actually survive. And, in the ideal situations, maybe even thrive.


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