Suppose a habitable planet is perpetually enshrouded with clouds but still has enough light seeping through to make lit and unlit portions of a day, and has an intelligent tool-making species living on it. Assume primitive civilization of some sort starts to develop. When would they start to need clocks, and how would they satisfy this need?

Keep in mind that the first "clocks" on Earth are likely over 5500 years old, and probably older. A simple vertical stick in the ground would have sufficed, but sticks of course rot. However, those first clocks on Earth were made in regions where the sky was not cloudy all day.

This question asks about the first clocks on a world where the sky is cloudy all day, everywhere, and remains cloudy all day (and all night) throughout the year.

Note: I am not asking about timing how long it takes to cook an egg. I'm asking about scheduling a meeting thirty days from now at 2:00 in the afternoon, or since it's a primitive society, scheduling a meeting thirty days from now sometime in the afternoon. Water clocks were notoriously imprecise, as were hourglasses.

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    $\begingroup$ Oh, the ancients had other kinds of time-measuring devices besides sun-dials. Sand-glasses, water clocks, calibrated candles... (Sand-glasses remained in widespread use to the end of the 19th century, for example for measuring the speed of ships. Originally, knots referred to the number of actual knots tied on the rope attached to a wooden log, which passed through the sailors fingers while a standard sand-glass emptied.) $\endgroup$
    – AlexP
    Jan 26, 2023 at 16:15
  • $\begingroup$ Is this world pitch black or just dim? because if light is at least somewhat present during the day then you could tell what time it is based on how bright the clouds look $\endgroup$ Jan 26, 2023 at 16:47
  • $\begingroup$ @redfrogcrab Just dim. There's still a dim daylight period and a dark nighttime period. Maybe a bit Venus-like, but not quite as bad as that. (Even Venus's surface has day and night.) $\endgroup$ Jan 26, 2023 at 17:05
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    $\begingroup$ We don't really have any proof (or even a hint of a proof) that obelisks were ever used as the gnomons of sundials; as far as we can tell, obelisks were not intended to be anything more than visually striking monuments. And the oldest sundials we actually have were obviously made as sundials, complete with hour divisions. (Perhaps suprisingly, the oldest water clocks ever found are roughly of the same age as the oldest sundials ever found, about the middle of the 2nd milennium BCE.) $\endgroup$
    – AlexP
    Jan 26, 2023 at 17:17
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    $\begingroup$ If the sun is hidden by the clouds, then getting a rough idea of the time just by looking at the position of the sun and the lengths of the shadows becomes harder. So I would expect a clock to be invented sooner than on Earth, because it's more needed. $\endgroup$
    – Stef
    Jan 26, 2023 at 20:49

10 Answers 10


There are 2 key purposes of Time:

1: future planning events and co-ordination (Meet me at 3 pm!)
2: Time elapsed (Cook for 5 minutes on high).

As others have eluded to, Hour glasses/Sand clocks/Water clocks would fulfill the function of point 2 - but these answers, although good - don't address a unified agreed sense of 'time'

Function 1, however is where a time system based off of the workable hours in a day becomes super relevant - you have a 'start' and a 'stop' period and then you subdivide that into approximately uniform graduations - these same graduations are used for function 2 for simplicity - but it doesn't answer how we get there.

My answer:

Tidal Based Time

You didn't specify if your fictional world has a moon or other heavenly bodies - but I'm going to presume it has one and that like on Earth, these cause Tidal flows. The Tidal flows are not obscured.

Now the Tidal flow isn't precise initially - but it's good enough and regular enough to know within an acceptable margin of error for a primitive society.

The other reason Tidal Flows are a great idea? Spring Tides - now we not only have Time, but we have a Calendar! Spring Tides occur at Full Moon or New Moon - giving us approximately 2 weeks (again, assuming a Moon that works like ours - but you can fiddle the variables as you see fit).

You can also add in King Tides (or Perigean Spring tides - to use the correct term) as denoting either changes in season or significant events (Religious or otherwise) etc. etc.

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    $\begingroup$ That's a neat idea, particularly for a planet doesn't have a large moon (or even worse, two large moons). Surprisingly, we've only had good models of the tides for about 250 years; this was an area where Isaac Newton pretty much failed. (Tides in the North Sea and English Channel are notoriously complex.) It was Laplace's dynamic theory of the tides that turned the boat around (pun intended). $\endgroup$ Jan 26, 2023 at 21:08
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    $\begingroup$ Another way to get seasons and years (and hence a primitive calendar) is to notice that the time the sky remains lit changes over the course of a year. That's assuming the planet either has a non-zero obliqueness or a non-zero orbital eccentricity. I'm liking this answer more and more as it not only yields a primitive clock but also yields a primitive calendar. $\endgroup$ Jan 27, 2023 at 13:40
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    $\begingroup$ I've chosen this over the top-rated answer for multiple reasons. The key reason is that it's rather primitive, which is what I wanted. Another reason is that evidence for the first tide-keeping society would eventually be wiped out by the ravages of time. The species would forget that they kept time by the tides before they invented water clocks. Moreover, a tidal clock is in a sense a kind of water clock. It would motivate some bright young individual to invent a drain-based water clock. While this assumes a coastal species, there's nothing wrong with that in a world building exercise. $\endgroup$ Jan 28, 2023 at 8:12
  • $\begingroup$ @DavidHammen - Awesome, you are most welcome - good luck with the rest of your story! $\endgroup$ Jan 28, 2023 at 18:35

Clocks don't exist to tell you when the sun will rise and set, they exist to coordinate the activities of people and events

When will clocks be invented on your world? Just as soon as the inconvenience of getting people together for an important meeting or activity outweighs the value of not having a clock (or the first time dinner is burned, whichever comes first).

From a practical perspective, clocks have nothing to do with the sun. Yes, here on Earth where we have a clear view of many celestial events, the development of clocks (and time keeping) was hugely light based. But as time progressed (hah...), we discovered that celestial events weren't as predictable as we needed them to be. OUr need for really precise time has forced us to define time (e.g., the definition and measurement of a second) in ways that respect, but exclude celestial events.

Long story short, you don't need light to have a clock.

As our own history of timekeeping devices suggests, there are many ways (and reasons!) to keep time. Even on your world, there will be (or, should be...) seasons. A cold season, a stormy season, a warm season, a "light" period, a "dark" period.... So the basic divisions incorporating the sun and the planet's rotation and orbit exist, just not as precisely as here on Earth.

Sand, water, incense, pendulums, candles... Anything with a reasonably predictable rate of consumption can be used to create a clock. In the end, your good people will end up with gears, then electronics, then atomics, for precision time.

In short, your people will basically build the same kind of timekeeping devices Humans did. They just won't depend on sundials much because they'll be too imprecise too early in your people's history.

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    $\begingroup$ Regarding "Clocks don't exist to tell you when the sun will rise and set, they exist to coordinate the activities of people and events": Exactly. Back when it took humans a long day to travel a mere 20 or so kilometers, "meet with me next Thursday" would have been good enough. At what point did "meet with me next Thursday" become not good enough? $\endgroup$ Jan 26, 2023 at 17:18
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    $\begingroup$ Note also that civilization managed fine for a long time with pretty crappy clocks, until navigation during long-distance sea voyages brought tougher requirements to timekeeping. So, the sophistication of timekeeping tech will likely be driven in part by other activities that nominally have nothing to do with knowing the time. And, if your very cloudy world has no oceans, they might be satisfied with rudimentary clocks for millennia. $\endgroup$
    – Tom
    Jan 26, 2023 at 17:24
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    $\begingroup$ People accidently invent clocks all the time. A staple of Japanese gardens is a deer scarer. A tube of bamboo that swivels on a pivot. When it fills with water it tips and dumps the water. Then returns upright with a loud thump that scares deer away. It's effectively a water clock that doesn't keep time. $\endgroup$ Jan 26, 2023 at 21:08
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    $\begingroup$ @tom +1. As soon as you need to know your longitude in the middle of the sea, they will offer money to anyone who can make a timepiece. Otherwise you don't need to know when it's 2PM; just that it's 30 days later, which is easy: stick 30 sticks into the ground, one per day. You wake up and go to the place we said to meet in 30d, and wait. If the economy doesn't demand it, then you can't have it. In a world w/o clocks, if no one knows when it's 2PM, then no one needs to know when it's 2PM. What kind of drive-yourself-into-the-ground-20th-century-stupidness has you in such a rush? $\endgroup$
    – Mazura
    Jan 27, 2023 at 0:47
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    $\begingroup$ @Mazura That doesn't work in this planet. Time doesn't tell you longitude. You compare time of celestial events between two points, and with knowledge of the rotation rate of the Earth, you determine longitude. (e.g. if the sun rises at 3 PM at home, and your clock says it rises at 3 AM, then you're halfway around the Earth) However, the planet is enshrouded in clouds so you can't even see the Sun, much less stars, so you're stuck. You'd need for somebody to get the idea for laser ring gyros or navigation satellites first. $\endgroup$
    – user71659
    Jan 27, 2023 at 10:34

Looking at the sun is the easiest, and probably earliest, way to tell the time. But in no way the only primitive one. Clocks would be needed by any intelligent race early in its development, as to not get surprised by the dark. This would be fairly crucial to the survival of the species. If sundials are unavailable for obvious reasons, then I'd assume some alternatives would pop up much earlier.

Water clocks and hourglasses are rumoured to have existed several millennia BC, and would probably be invented earlier in the timeline in your setting. Alternatives like the Asian Incense clocks could be an option too.


Might be unreliable, but use how bight the sky is plus some math to tell the time

We're going off relative brightness here

Start with how bright the sky looks, If it's bright, it's day, if it's dark, it's night.

Then, go with how bright or dark it is (this bit is tricky), if it's slightly dimmer than usual, then it's either early morning or late afternoon, if it's relatively bright out, it's most likely noon. (it may be hard to tell)

Use the light level of what came before now to determine the time of day. (Example: It was dark out earlier, now it's dim but light is here, so it's probably morning)

Divide this cycle up by any fraction to get hours, thus you have a basic system to tell the time, pair this up with either an hour glass or some other primitive non-light-based time measurement tool and you have a way to keep things on track

  • $\begingroup$ The "divide this up" step is going to be hard when they have no way of quantifying the duration between periods of brightness. $\endgroup$
    – Tom
    Jan 26, 2023 at 17:59
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    $\begingroup$ 50 shades of grey and there's a name for everyone of them,+1. O'Dark-Thirty $\endgroup$
    – Mazura
    Jan 27, 2023 at 1:02

Cooking and Water Clocks

One of the first things that civilizations will want to have a good measurement of time for is cooking. Whoever is doing the cooking will want to cook something long enough, but not too long. At first there will be traditions passed down like "go get 10 buckets of water from the river, and when you're done getting the water, your meal will be cooked" but eventually this won't be good enough and people will invent....

The water clock.

This device will allow a consistent interval of time to be measured, and functions very much like an hourglass, but without the need for all the things you'd need to build and hourglass.

Now we have an egg timer (or whatever other time interval is good for cooking the food in your world)!

  • $\begingroup$ I'm not asking about how timing how long it takes to cook an egg. I'll clarify the question; I'm asking about agreeing to a meeting a month from now at 2:00 PM, or even a month from now in the afternoon. Water clocks were notoriously imprecise. $\endgroup$ Jan 26, 2023 at 20:44

Not a complete answer, but I have to mention sunstones.


Quick summary:

There is a debated device in history, a glassy stone with which it is theorized that you can locate the sun's position even in foggy and completly overcast skies.

Where does this theory come from? There are artifacts found on ship wrecks and ruins of old colonies and town and old written texts about such stones.

Also people tried to replicate this in the present and the results were mixed.

But the physical principles are there and it works. The question is more like "will it work every time and everywhere on the planet?".


I don't think there is any way to (reasonably accurately) detect the time of day if the skies are cloudy (especially if the thickness of the layer of clouds varies from day to day). It may be good enough to reset a time kept by other means if it drifts too far from the natural day, however.

If you keep time by other means (hourglass, water clock, mechanical clock mechanism) you have two problems- first to synchronize the various timepieces so that people will agree on the time. The second is to reset the time when it drifts too far from the natural time of day.

This is somewhat similar to the problems faced by the designers of PTP (Precision Time Protocol). Dealing with communication channels with delays of unknown and somewhat variable times (since it's presumably insufficient to have just one master clock in a primitive society without electronic communication).

They could have a master clock (which the chrono-priests reset from time to time, perhaps adjusting it in small increments in the middle of the night to correspond to their observations of the average sky illumination).

At daybreak or thereabouts (at a known time on the master clock) messengers could be sent out to far flung places with timing devices that are capable of roughly measuring the time to and from the distant spot. The total time to and from could then be calculated and the remote clock adjusted to be synchronized fairly accurately with the master. The remote clocks need only keep time accurately enough between messenger visits and do not require the services of sky observers to reset the times. The jitter in messenger transit times could be compensated by only adjusting the remote times partially at each visit, so the adjustments are averaged.


Magnify the Sundial behaviour until it works

A sundial's problem on a cloudy day is that the light intensity isn't strong enough to produce a clear contrast of light and shadow on the dial.

So make it bigger, and invert it.

A human eye works by creating a large dark volume and a small aperture for light to enter.
If you create a large circular walled space and give it a partial roof with a hole in the middle, you'll find that the light forms a distinct spot-light effect in the room.

You can then tile your floor with markers for different times of day based on where the light starts and finishes over the course of the day.

It might look like a smaller version of this:

enter image description here


When would they start to need clocks, and how would they satisfy this need?

The Quest for Longitude

As some comments have noted the need for precise time keeping depends on human activities.
Meetings, fairs, commerce, religious events could all be held without the need of knowing exactly the current hour (and minute).
Then humans started navigating around the globe and encountered a big problem: the need to determine their position on the surface of the globe.
On Earth latitude could be inferred quite easily by the maximum height of the sun on the horizon. But longitude while seafaring remained elusive for a long time. (*)
This was no small matter. In 1707 a fleet was shipwrecked because it could not determine its position accurately. Scilly naval disaster of 1707
This prompted even more the efforts from society to find ways to determine longitude.
The proposed method (and the one that was later successfuly implemented) was requiring to know the time exactly.

To know one's longitude at sea, one needs to know what time it is aboard ship and also the time at the home port or another place of known longitude—at that very same moment. The two clock times enable the navigator to convert the hour difference into geographical separation. Since the earth takes 24 hours to revolve 360 degrees, one hour marks 1/24 of a revolution or 15 degrees. And so each hour's time difference between the ship and starting point marks a progress of fifteen degrees of longitude to the east or west.

"Every day at sea, when the navigator resets his ship's clock to local noon when the sun reaches its highest point in the sky, and then consults the home port clock, every hour's discrepancy between them translates into another fifteen degrees of longitude. One degree of longitude equals four minutes of time the world over, although in terms of distance, one degree shrinks from 60.15 nautical miles or 111 km [Earth's circumference being 21,653.521 nautical miles, or 24,901.55 statute miles at the Equator], to virtually nothing at the poles

Dava Sobel's - Longitude

How the clock came to be, what challenges had to be overcome to have them running accurately abourd ships rolling in the ocean, with all kinds of weather, the struggles, the antagonists competing for the prize, falls and triumph. It's all in this throughly enjoyable book. I advise anyone here on worldbuilding to read it.

(*) In your world I don't know if the sun is visible at least as a vague circle in mid day, like you often have on a cloudy day. I assume its position can be determined as the light is bright enough on the planet for evolved life to develop.

TLDR: the first real NEED would be the quest for longitude. Anything before that was just a 'nice to have' instance.

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    $\begingroup$ The quest for longitude started thousands of years after the first clock was invented. $\endgroup$ Jan 27, 2023 at 11:22
  • $\begingroup$ I know. But OP is asking for the NEED of it, as I reported in quote. $\endgroup$ Jan 27, 2023 at 11:44
  • $\begingroup$ I'm the OP. I'm assuming an ancient need for clocks, not a nearly modern one. 300 years ago is essentially modern. $\endgroup$ Jan 27, 2023 at 11:50
  • $\begingroup$ You are the OP's author, not the OP itself :) OP= Original Post. $\endgroup$ Jan 27, 2023 at 12:38
  • $\begingroup$ Anyway my argument is that without any fabricated need for clocks for your race (e.g. religious ceremonies) the first real NEED for precise time keeping for mankind happened with the quest for longitude. All previous clocks devices were not exactly needed. $\endgroup$ Jan 27, 2023 at 12:42

Going for super-simple here...

First a bit of Earth history, in old London, there was a lady who would tell you the time in exchange for money. I presume she got the actual time from Greenwich, then travelled to the centre of the city and "sold" time to people who couldn't get to Greenwich or didn't have a watch or way to maintain time between trips to Greenwich.

As noted, sand-based hour glasses, water clocks, etc are all a bit inaccurate. However, they were used extensively because they're often good enough. You can operate by sand-clock in your world. When the sun comes up, a timekeeper turns over a large sand clock (hour glass). This clock has been carefully crafted to be as regular as they can make it, and keeps running for as long as there's sunlight.

(You don't say if there are seasons - if there are, then the clock can have graduations on it which show when the day will end at different times of year).

People in the city can visit the clock to get the time, or perhaps "buy" it from enterprising people like the old lady in London. It is now possible to say "let's meet at 3pm", because everyone in the city is using the same "source of truth" (at least within a reasonable degree of accuracy). This works over a pretty broad geography - certainly 10s of miles.

Seasons (and so dates of the year) can be managed a similar way. Each day the time keeper turns the sand clock, (s)he also puts an extra slick into the ground, or puts an extra log on the pile or whatever to count the days (so far) this year. By all means break that counting up into chunks (like months or weeks). As we do, convention and prior knowledge tell us that (in the Northern hemisphere) you can expect it to be cold in January and have short days - the same thing is possible in your world (although measuring years gets tricky if there are no seasons - but in that case, a year can be "100 days" or whatever you like because it doesn't really matter where around its star the planet is).

The main principles here are:

  • do the same thing every day/week/month/year - or whatever indicators of time passing you have (as others have noted, maybe the tides, or because the wind changes every few days or whatever).
  • Get everyone to follow the same system of time (or at least everyone in a locality).
  • Provide a way to know when the unit of time (eg. day) will end, so they can plan things throughout the day and not be half way through something when the light fades

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