I previously asked about the possibility of a fantasy world that has a different sun every day and where, on random days, no sun rose: World with a different sun every day, and random days with no sun. I am now looking for the possible effects such a phenomenon would have on the medieval civilizations of this world, focusing on the dark days concept. Basically, 2-4 times a month, on random days, no sun would rise, leaving the world in darkness until the following day.

First, concerning climate: How low could the temperature drop in that time period (in average 36 hours without sunlight)? Could there be sudden snowfalls in summer because of this? Would there be seasons at all? Would these dark days have long-term consequences on the climate of the planet? If there were two or more successive dark days at some point, would the effects be significantly more important?

Second, concerning life: How would it affect fauna and flora (would they survive easily or would they have to adapt to some consequences)? What human activities would likely be disrupted (for instance, travel (by foot, horse or sea), agriculture, hunting/fishing, construction)? What would people whose activities are affected do to deal with this situation?

Finally, would there be other important consequences I haven't considered?

  • $\begingroup$ @kingledion I removed the science-based tag. On my other post, I was looking for possible causes of the phenomenon, but here I am looking for its consequences on the world. $\endgroup$ – Dzarak Mar 27 '17 at 19:27
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    $\begingroup$ How earth like is this fictional world? The Earth has thermohaline circulation and a few other heat redistribution techniques, but if your fictional world isn't earth like, it'd be very hard to speculate on. Additionally...when no sun rises, is that the entire world in darkness? Or does the sun revolve once around the planet and fully disappear for a day? $\endgroup$ – Twelfth Mar 27 '17 at 19:37
  • $\begingroup$ @Twelfth This planet is very much Earth-like, but changes can be made in function of what I need. What happens on the other face of the planet is irrelevant, since I do not plan on going there, and the phenomenon is described only from the people's perspective on this main face (but, as someone suggested in my other post, it could be something like a tidally locked planet whose dark side is lit by multiple moons reflecting the bright sun's light, so the other face would be constantly lit by the real sun). $\endgroup$ – Dzarak Mar 27 '17 at 20:11
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    $\begingroup$ Welcome to Worldbuilding! You ought not choose an accepted answer so quickly — generally wait 24 hours for more people to answer first. $\endgroup$ – JDługosz Mar 28 '17 at 0:35
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    $\begingroup$ If you want to follow up with more questions on this world of yours, you might make use of the sandbox post on Worldbuilding Meta. $\endgroup$ – JDługosz Mar 28 '17 at 0:40

Two questions, two sections to an answer. I have some confusion as to how / where the sun disappears to only reappear the next day, but can still work with this.

Climate - One of the best ways to view what is happening here is simple energy. Lets say the Earth receives x energy in the course of a day, or 365x over the course of a year. 2-4 days per month (we will average it to 3 days per month) is 36 days of no light, or about 90% of the total energy from the sun. Now you can make up for it, as 36 days of the year could have a sun with double the energy...otherwise one would expect lower temperatures around the globe.

Ultimately climate/weather can be considered the redistribution of energy across an unevenly heated globe. Thermohaline circulation, also known as 'the great energy conveyor belt' is a process where warm water from the tropics flows along the surface to the polar regions, cools, then descends and travels back to the tropics. Even a globe without a sun for the day will continue to see this circulation continue...it will keep temperatures somewhat consistent around the globe (IE, tropics cool at same rate as polar regions during the 'no sun' days).

Back to the weather statement...if weather is the redistribution of energy across a unevenly heated globe, than increasing the amount of uneven heating (a day with sun vs a day without) you are going to significantly increase the forces that are redistributing this energy. I would expect much higher winds on this planet, and not just on the sunless days.

Plant life is easily adaptable I would beleive...there would be a need to store and increased amount of energy for the longer days and these plants would likely be forced to find a way of saving for the sunless day. Most likely this will result in more advanced root systems that can be used to store the food. animals that eat roots (boars for example) would likely have a bit of an edge in locating food. The advanced root system would also help vs the winds and erosion that these sunless days would cause.

Multiple sunless days in a row would be a more extreme event, but would not be catastrophic by any means. The temperatures would dip significantly, but creatures evolving in this world would have adaptations to help them survive these events.

Culture - The sun is at the core of much of religion as the light/heat/energy bringing being from above. A disappearing sun would be heavily reflected in these religions, likely as a sign/omen (I'd actually think a different sun everyday would drive a 'red sun = glory in battle', 'orange sun good for planting', etc...). A disappearing sun could easily represent a gods wrath blocking the energy lifeblood to this planet.

This is more speculation...but part of Stonehenge appears to be rooted in the sun, in particular the winter solstice where the sun disappears for the longest time in a year. I've seen a TV special that speculated there would be rituals around calling back the sun for the next year and the next rotation. If the sun disappeared for a day, you would expect some sort of ritual 'pacification' of the gods to ensure they returned the sun the next day.

I would suggest Astronomy would be a much further explored science...much of our limitations in viewing the starscape comes from the sun as it interferes with our ability to see the starry sky. With no sun (and therefore no moonlight), the sunless star scape would be impressive and I would speculate beliefs around the stars coming out to inspect earth during these days.

Important other considerations:

  • Gravity. No sun = no gravity = nothing to pull on earth, letting it drift in one way or another. This would cause an increasingly unstable orbit and may severely increase the level of tilt the planet has increasing seasonal effects. I doubt you could get anything close to a stable orbit during this and there will be very much a lack of consistency on this world. Farmers would have far more of a guessing game as to when to plant crops (a giant belief structure around predicting when to plant would likely come about) and it's questionable how self sustaining farming really could be. You can handwave all this away, but there is a certain level of disbelief that this setup could result in anything resembling stability.

  • Tides. Same thing as above, but the tidal components of this globe would be horribly unpredictable, even more so if it lacks moons.

  • $\begingroup$ I think you pretty much answered all my core questions. Thanks a lot! $\endgroup$ – Dzarak Mar 27 '17 at 22:17
  • Climate - I think there's a few too many variables to really pin down a definite answer.

The climate of the whole planet, I think, is basically determined by how much energy it gets from the sun, paired with what the average atmosphere is like.

So, if you wanted this hypothetical to be Earthlike despite what you've proposed, simply put it a little closer to the sun on days the sun's there, or give it a slightly thicker atmosphere on average, so the greenhouse effect is a bit more pronounced.

As for plants, while there definitely would be an effect if this started happening suddenly, I'm sure they'd be able to adapt just fine and live stably. There are shade-growing plants here on Earth, and plants make it through the night (and even the winter) just fine. They would, on average, get a little less sun than the plants on earth, but they could adjust to that, I'm sure. They'd store a bit more food, the cut-off for where plants could survive in the shade would be a bit brighter, and the full-sun plants might not be quite so spreading, but I don't think it would be really noticeable.

In short, I don't see any really predictable affect on the climate. With more preconditions, you could probably set a few up, but as-is, any one effect I might predict could simply be balanced back by another effect you haven't defined.

  • Culture... this one is a bit trickier, but I'd say about the same, and for one simple reason.

Random days of darkness.

If these can't be predicted, but happen fairly often, people are simply going to adjust... and then start ignoring them. Sure, they may not go out and farm/fish, but it's not like we don't already have weekends. This is like someone one a desert planet posting the question: "What would it be like on a planet where it rained randomly?" It seems interesting and dramatic, but the truth is that familiarity breeds contempt.

There might be some secondary or tertiary effects; light be less symbolic of 'good', darkness might not be feared quite as much, but this also comes down to individual culture, and isn't really the sort of thing that can be postulated with any certainty. Like how white is the color of death in some cultures, but black is in others.


Imagine a parallel world where it rains every morning for an hour after sunrise, with clockwork-like regularity. Further imagine someone in such a world, asking his friends "What would it be like if the rain didn't fall on some days, in an unpredictable manner?"

Answer: If there were no knowledge of anything different, people would simply accept the situation as "normal".


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