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I am currently working on a fantasy world setting and I had this idea about a world having a different sun every day. There could be around 3-12 suns in total, and every day, a different one would rise and set. Each sun would have, say, a different color, size and brightness but there would not be major differences between them. They can come in a specific order that gets repeated, or come randomly, I don't mind. Moreover, there would be days, unpredictable, when no sun would rise, leaving the world in darkness until the following day. These dark days would come 2-4 times a month on random days.

Is there any way that science could explain such a phenomenon, or at least something similar? It is not mandatory, but I would like a scientific explanation if possible, even if I have to modify this idea. This fantasy world exists in a larger science-fiction universe, so this phenomenon could be created artificially by other more advanced civilizations. Also, I describe the phenomenon from the perspective of people on this planet, so I don't care what happens outside of it to make it work.

EDIT: It doesn't even have to be actual suns, but it could very well be things that look like suns and give off enough heat and light for the civilizations to survive (as long as the planet is still in orbit around something).

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    $\begingroup$ What should happen at the antipodal point of the observer that sees the behavior you describe? $\endgroup$ – John Dvorak Mar 27 '17 at 16:45
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    $\begingroup$ correct me if i'm wrong, but with that number of suns, unless they're orbiting a stationary point where our sun is, and orbiting in line with say venus, and your planet is around jupiter, i dont think you can have only one sun per day, and i dont think that days without a sun can happen $\endgroup$ – Alex Robinson Mar 27 '17 at 16:47
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    $\begingroup$ Welcome to the site, Dzarak. Please note that questions along the lines of "How will this change affect society?" are immensely broad topics and, thus, ill-suited for the Stack Exchange format. You may want to consider removing your second question and asking follow-up questions with targeted interest. $\endgroup$ – Frostfyre Mar 27 '17 at 16:52
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    $\begingroup$ The Three-Body Problem by Liu Cixin, excellent English translation by Ken Liu. $\endgroup$ – AlexP Mar 27 '17 at 17:57
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    $\begingroup$ With the edits I would say this is fine. Basically, can this system exist... $\endgroup$ – James Mar 27 '17 at 19:18

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An easy and noncrazy way to do this is to have the planet rotate with a period equal to its year, like the moon does the earth. Thus there is no day or night: the sunward face is always sunward. The sun is extremely bright so not much happens on the bright side of the planet.

Serving the role of suns on the dark side are various moons. Because the sun is so bright it is reflected with more or less the power of a sun by the various moons. One could then tweak the moon characteristics to change the quality of each "day". For example a close, small, very reflective moon (perhaps metal - a captured asteroid?) would make a very bright day. A reddish Mars-like moon would make a red day. Blue moons would be infrequent. And so on.

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    $\begingroup$ You could get a fair bit of heat via atmospheric convection from the hot side. I am a little worried about energy adequate to grow plants from moonlight. Our sun is a lot brighter than our moon. But it does not seem a stretch to me to posit a sun much brighter than ours, and moons closer (the Martian moons are a lot closer) and more reflective. $\endgroup$ – Willk Mar 27 '17 at 20:22
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    $\begingroup$ TrEs-2b has asked a bunch of questions about a world with a 9-year day, so those are pretty relevant to this answer. For example, here's his question about weather on that planet $\endgroup$ – Rob Watts Mar 28 '17 at 17:34
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    $\begingroup$ FYI: Planets rotating at their orbital period is also tidal locking $\endgroup$ – Ferrybig Mar 28 '17 at 17:36
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    $\begingroup$ @Will I wouldn't worry about plants in general, so long as you aren't married to having plants from real Earth. Plants have evolved to the conditions available, if conditions were different something plant like would still have evolved. Life is more adaptable than most people give it credit for. $\endgroup$ – Myles Mar 28 '17 at 18:40
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    $\begingroup$ Would this still fit with the "random days with no sun"? Seems like moon orbits would be fairly predictable. $\endgroup$ – David Starkey Mar 29 '17 at 14:08
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Note: I started this answer by writing up all sorts of wiggle room about the word "day" not intending to come up with an answer. Then I came up with a crazy explanation (rogue planet). And finally and then hit on a plausible one (variable star) that doesn't rely on any of that. I've reordered the answer to put the best answer first, and left the rest in because it's interesting.

Variable Star: Same Star, Different Day

A variable star is a star whose brightness and other attributes fluctuate. These fluctuations can be regular, or irregular. They can be big, or they can be small. They can be caused by changes in the star itself, or by things blocking the star like a dust cloud or swarm of comets.

A planet around an irregular variable star which has both internal and external causes would seem to see a different star every day. The changes in the star itself, plus the various occluding objects in closer orbits around the star, would make it seem "random".

For example, what if our planet had a gas giant in a closer orbit. That gas giant has trapped debris in large clouds at its L4 and L5 points.

enter image description here

Source

These clouds act like giant filters giving the star a different color, intensity, and apparent size in addition to the variations in its actual size. As the gas giant and our planet rotate relative to one another, one field or another (or none) will partially occlude the star. Throw in more than one interior gas giant, each with their own debris field, and you have a heavenly kaleidoscope!

The debris fields are diffuse enough, the variability slow enough to never see an abrupt change. The planet's rotation is fast enough to never have enough time in a day to observe a slow change. To a layman the star sets while fuzzy, small, and red (filtered through a debris field), and when it rises it's sharp and blue (it's fully passed the debris field).

On top of that, there will be normal changes in the appearance of the star as it travels across the sky due to its light passing through different parts and thicknesses of the atmosphere, just as our own Sun looks different at sunrise and sunset and in different parts of the world in different weather. This further complicates anyone figuring out they're looking at the same star without careful observation and consideration.

Until they figure out the very complicated and unstable orbital mechanics of their system, it will appear to them as if they look at a different star every day. Until someone can coordinate tracking their star's changes over a full rotation, nobody can prove it's the same star changing its appearance. This could be a key plot element of the story, people's observations are converging on the conclusion that it's been one star all along, and that threatens some political power based on the orthodoxy of a new star every day.

This configuration does not have to be stable, if it lasts for 10,000 years that will be long enough for it to be "normal" for all of a planetary society's history.


Sidereal vs Synodic Day

There's some issue with the notion of a "day". On Earth there's the sidereal day, and then there's the synodic day. We're used to them being basically the same, but what if they weren't? What sort of culture would grow up around that and what notion would they have for "day"?

The sidereal day is what an astronomer might use for a day. It's the time it takes for the planet to make one full 360° rotation. A planet bound observer can measure this by tracking the angle of the (relatively) fixed distant stars.

Then there's the synodic or solar day, that's the time for a point on the planet to come around and face its star again. It's sunrise to sunrise. That's what your average person would call a day.

They're not the same on the Earth. Because the Earth rotates in the same direction as it orbits (as do most planets) it has to go a little bit further to line up with the Sun again. A synodic day is 24 hours, but a sidereal day is about 4 minutes shorter.

enter image description here

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This is the wiggle room in the requirement. Since the question talks about "having a different sun every day" this is the synodic day: sunrise to sunrise.

Who Cares What Happens On The Other Side of the World?

Furthermore, a low tech society wouldn't be able to communicate or travel to the other side of the world. Their notion of "day" would be what they see in their sky. Whether there's another star shining in the sky in the other side of the world would be of no consequence to their notion of a "day".

I Wish There Was More Time in the Day

And then there's the length of the day. We're used to a "day" being a very small fraction of the year, but there's nothing that says it has to be. For example, because Mercury rotates so slowly, and it's so close to the Sun, its solar day is two of Mercury's years! It's tidally locked to the Sun.

Lacking any significant axial tilt, Mercury doesn't have any seasons; there's little difference to Mercury whether it's on one side of its orbit or another. A culture growing up on a Mercury-like planet which is in a star's habitable zone wouldn't have much use for a "day" or "year" as a measure of time.

All this adds up to some more wiggle room to make it work.


Rogue Planet

This is a variation on the novel A Deepness in the Sky which I highly recommend.

What if we had a rogue planet with life that has adapted to the relatively brief periods it's warmed by a star? What if the reader is not made privy to this, and the characters just talk about a "day" as if it's perfectly normal?

There's nothing that says life, even intelligent life, has to have a metabolic rate as high as Earth life. This life has evolved to very carefully husband and store energy. For most of the time life hibernates underground, nearer to the well insulated planetary core, warmed by the left over heat from its gravitational formation, and the decay of radioactive elements. As it drifts near a planet, a new "day" begins, the surface becomes briefly habitable, and life pours out onto the surface to take advantage of the increased energy available.

This surface explosion of life could take dozens, hundreds, or thousands of years depending on how close the planet has drifted to a star and how large that star is. This doesn't necessarily have to be in the habitable zone for liquid water, imagine the relative bonanza Pluto has compared to a rogue planet in deep space.

Let's say this planet has a very, very slow rotation. As they near a star it might come above the horizon looking a bit bigger than the rest. As they drift closer and closer, parallax will make it appear to move through the sky, getting a little larger. As the planet warms, life would pour out onto the surface for the new "day", their metabolism rising to make the most of the available energy.

At "noon", their closest approach to the star, it would appear largest in the sky, then start to shrink as the planet moved away. Their metabolism would slow and they'd start storing energy for hibernation as the planet cools. "Sunset" would be when they can no longer distinguish their star from any other in the sky and they'd return to their hibernation.

The next time they come to the surface, it's a new "day" around a new star!

You can even play with the planet's rotation and some temporary chaotic orbits to come up with even crazier days.

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  • $\begingroup$ I like the variable star idea! I'll think about it, thanks for the answer! $\endgroup$ – Dzarak Mar 27 '17 at 20:04
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    $\begingroup$ i'll be damned, thats an amazing answer $\endgroup$ – Alex Robinson Mar 27 '17 at 20:40
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    $\begingroup$ I think that the last solution is the most poetic one... Good work! I love that idea :) $\endgroup$ – frarugi87 Mar 28 '17 at 8:22
  • $\begingroup$ @Dzarak The last answer is very nice. Assuming the metabolism is affected by the "daytime" it could be argued that the "feeling" of time is also affected by this. So lets say "daytime" is 12 hours and "nighttime" is 3 days (random numbers here) but it is felt the same length because they also think slower when it gets darker. It would be a continous process not as discrete as I described here. $\endgroup$ – Kami Kaze Mar 28 '17 at 9:09
  • $\begingroup$ Please give credit and attribution for the images that you take from the internet for use in your posts. $\endgroup$ – Lightness Races in Orbit Mar 29 '17 at 11:27
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A recent novel, the Three Body Problem by Cixin Liu, did more or less exactly what you describe - you don't need many Suns, you just need a chaotic orbital system so that it appears that there are many Suns.

As the planet travels in a chaotic path between three suns, the suns will sometimes be very close, and sometimes very far away; sometimes there will be one in the sky, and sometimes three. The colours of the suns will be affected by their relative distance, the atmosphere, and other interacting factors.

Secondly, the chaotic component of the Suns would create such a difficult environment that it would 'reset' the culture at those times when the planet became too hot or too cold, so it would be very hard for any culture to rise beyond a relatively simple point. So, when the heat got too great, all cities would burn, while deep dark long winters would occur when the planet deviated on a long orbital trajectory away from all three suns.

The main problem is, as I have just said, the book has already been written, so you would need to find something in the story that differentiates it from Cixin Liu's novel.

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  • $\begingroup$ I'm looking for something more stable and preferably only one sun (or none) in the sky at any given time. I wasn't aware of that novel, so I'll go check it out, thanks! $\endgroup$ – Dzarak Mar 27 '17 at 17:12
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After considering the problem, I have come up with a partial solution, which relies on having different suns / no suns, but not randomised, also a solar system which probably has about a 0% chance of actually happening, but still: hand drawn solar system

The logic is this: the gas giant and "earth" have the same year, "earth" has whatever day length you want, but the key bit is the stars: your main star is HUGE, such that it can have two stars orbiting it that are not opposite eachother. We have a gas giant to block out the view from the other 1 or 2 stars, so that in theory you should only see 1 at a time, and never directly see the primary star, only a secondary or none at all

Beyond that, pick how long the secondary stars' year is, so that you have a relatively regular order, secondary1, secondary2, no star, secondary1... etc

I am not fluent with astrophysics, or large scale mechanice so I don't know how stable the orbits would be, and have some doubts as to whether they would be stable for a long enough time for planets / life to develop, but use "handwavium" which is a writers favourite element to make it work

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  • $\begingroup$ I like that! But I also liked the unpredictability of the days with no sun... Still, it's a good idea, thanks! $\endgroup$ – Dzarak Mar 27 '17 at 17:32
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    $\begingroup$ @Dzarak i considered other systems with more suns and more complexity, but the problem is you have to balance the masses of the stars, figure out how to hide enough of them so that you always only see 0,1,2 suns at a time, and include a random / chaotic element that wont decay in such a manner that your suns simply combine, im gonna ask over in physics SE because now i'm curious $\endgroup$ – Alex Robinson Mar 27 '17 at 17:34
  • $\begingroup$ Alright, let me know if you find something! $\endgroup$ – Dzarak Mar 27 '17 at 17:43
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    $\begingroup$ 'the gas giant and "earth" have the same year,' I don't believe two planets can have the same orbital period and have one orbit inside the other. They'd need the same orbital period, and orbital period depends on the semi-major axis of the orbit. Nice effort! $\endgroup$ – Schwern Mar 27 '17 at 18:18
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    $\begingroup$ @Schwern "probably has about a 0% chance of actually happening, but still" i am aware that this scenario is unlikely, but because the question is novel driven, you can have unlikely answers, you just need some outside of the box thinking to get the answers $\endgroup$ – Alex Robinson Mar 27 '17 at 18:23
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Doughnut world with an eccentric tumble. The tumble causes different amounts of atmosphere to refract the sunlight. This would probably have to be artificial to survive the tumble long.

The system the planet is in could have orbiting anomalies that change the appearance of the sun. Perhaps there is even a partial Dyson swarm (abandoned or otherwise) that blocks out the sun entirely from time to time.

The planet actually orbits a black hole, not a sun. The light seen from the surface is released from the in fall of mater into the black hole. Changes in the mater, volume and make-up will affect the visible light. Sometimes it might even be absent entirely. There are other repercussions.

The planet is not part of a singular star system. It actually wanders a nebula who’s ambient temperature is high enough that the energy production of the planet combined with its thick atmosphere keep it at habitable temperatures. It’s position within the nebula determines what if any sun’s/stars cause day rise.

The planet is a habitable moon. It has a figure 8 orbit around two planets (probably gas giants) and through their shared center of gravity. The two planets are tidally locked to each other and revolve around the center of their shared gravity. The moon gets light from the sun, and from reflection off the surfaces of the two gas giants. Depending upon the revolution of the gas giant pair, their orbit around the sun, the position of this moon and throw in potential eclipses from other moons and you can get a rather erratic day/night/partial day/ partial night cycle.

The planet is inside/at the center of a Dyson sphere like object. The internal surface of that sphere projects some sort of illumination that is perceived as the sun. Since it is artificial it can change randomly.

Handwave, the planet cycles through realities/planes of existence.

Several of these are stretches. Though technically possible. All of them have larger consequences. You’d have to pick a specific “cause” to get fine grain details as to the affect.

In general though you no longer have a regular day/night cycle or a regular week cycle. Everything that has arisen in our society because of this regular pattern would break down. There is no regular work week. There is no standardized time keeping or date keeping. Nature has evolved animals to take advantage of earths regular day night cycle. So this planet would evolve different life cycles based upon the random elements.

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  • $\begingroup$ Interesting! I might consider some of those and elaborate on it. $\endgroup$ – Dzarak Mar 27 '17 at 18:21
  • $\begingroup$ This sounds like something that could happen in a globular cluster. Radiation would be severe, as would temperature range. The planeshift idea is nice too. $\endgroup$ – Konchog Mar 27 '17 at 18:58
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Consider a type of constructed megastructure such as a shell world. Each layer is like a floor in an apartment building, and some levels are set up to appear like a natural “surface” planet, but it’s really an ellaborate terrarium. Most of the shape of the mountains and seas are molded into the floor.

Since this is inside, what to do about the sun? The sky is the ceiling of the level, which could be many miles up. It is a rich display screen which fakes the appearance of stars etc. and programs in a display of the daily sun, with its seasons.

Only something got messed up in the software, or maybe the zookeepers were feeling like a creative experiment. For whatever reason, the parameters of the sun changes from day to day.

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You maybe want to look into Nightfall

The fictional planet Kalgash is located in a stellar system containing six suns (Onos, Dovim, Trey, Patru, Tano, and Sitha), which keep the whole planet continuously illuminated; total darkness is unknown, and as a result, so are all the stars outside the planet's stellar system.

You can have "suns". What you don't need is "human" civilization.

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As far as the effect of unnatural "suns" goes, I suggest you read The Second Chronicles of Thomas Covenant. A magical effect called the Sunbane gives the Land a range of suns that could rise every day, each causing abnormal environmental behaviour: unnatural growth of plants, extreme floods, immediate drought, and widespread pestilence/disease.

As for how this could happen...

If some object lies between the planet and the sun, orbitting the sun synchronously with the planet, then it could selectively filter the sun's rays. A closer-to-the-sun object will not naturally orbit in lockstep with the planet though, so this object would need to have its own means of propulsion. You'll also need to decide why anyone would create this.

A Dyson bubble could avoid the need for this whilst still letting light through, and unlike a regular Dyson sphere is self-stable. Different places on the Dyson bubble will naturally retain different amounts of light depending on what's in the way, so will affect the sunlight getting to further-out planets. If you're looking for universe creation to hang more stories on, this would be my choice. It's hard-science-friendly, there's a solid rationale for creating it, any effects on other planets are accidental so you don't have to presuppose planetary-scale experimentation, and best of all from a storytelling PoV it gives you immediate access to a whole new set of societies within the same solar system.

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  • $\begingroup$ Nice idea! Also, I'll go check out the Thomas Covenant Chronicles, thanks! $\endgroup$ – Dzarak Mar 28 '17 at 16:08
  • $\begingroup$ The sun was not actually changed. The Sunbane field was essentially a magical lens over the Land that caused the light of the sun to randomly be 1 of several different types, each of which had a unique (and generally devastating) effect on the Land. $\endgroup$ – Michael Richardson Mar 28 '17 at 16:33
  • $\begingroup$ @MichaelRichardson Hence my suggestion of something in between the sun and the planet... $\endgroup$ – Graham Mar 29 '17 at 10:19
  • $\begingroup$ I was going to answer this too, but its way to similar to your answer: a transparent, artificial construct, constructed by unknown forces aeons ago, which will shift the color and intensity of the sunlight passing though. While its magic for the minor beings at the planet, it was a mere disco-light for a space-faring civilization, or something more practical, like a giant "yo SETI here we are" notification. Even more - with color and intensity you can decode information, so it might be an interstellar network relay. $\endgroup$ – Confused Merlin Mar 31 '17 at 11:13
  • $\begingroup$ @ConfusedMerlin Nice idea with it as a transmitting device - that's the kind of practical reason I was thinking of for this existing. I guess I'm a bit jaded with the "extinct ancient race with mad skillz" trope though, because it lets the author get away without putting things on a proper foundation. It's too much like "a big boy did it and ran away" for me. That it exists and it's beyond the comprehension of people on the planet is fine, but it shouldn't be beyond the comprehension of the author. ;) $\endgroup$ – Graham Mar 31 '17 at 11:32
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I only have a partial answer, as everyone else has covered this nicely. Here are just a couple more things to consider, and probably integrate with other answers.

The planet tumbles chaotically

There are a few moons in our solar system (one around Saturn, the rest around Pluto) that instead of rotating consistently around one axis in a periodic way, tumble and rotate every which way due to the gravitation of nearby bodies. This depends on the planet you're on being more potato shaped than round (and defying the IAU definition of a "planet" in the process), but its worth considering. Here is a source discussing how this applies to at least two of Pluto's moons:

He’d been looking at how Nix and Hydra, the two largest of Pluto’s small moons, got darker and brighter as they traveled through their orbits. With the help of some new computer simulations, he realized that these two oblong moons were chaotically rotating—tumbling rather than spinning like tops.

“If you lived on Nix or Hydra, you would not know if the sun is coming up tomorrow,” Showalter says. “Or it could rise in the west and set in the north.”

Only one other moon, Saturn’s moon Hyperion, is known to perform such an off-kilter jig in space. In the Plutonian system, Nix and Hydra tumble about because they orbit both Pluto and its abnormally large moon Charon, which together form a gravitational dumbbell that tugs and nudges the moons in random ways. Styx and Kerberos also orbit the binary system formed by Pluto and Charon, so they are probably tumbling as well, Showalter says.

The planet isn't round, but instead a torus

Amazingly, a planet shaped like a torus would be stable. It is extremely unlikely to form naturally, but if it did there is nothing about the shape that would cause it to be torn apart or crush itself into a ball. Here is a source where someone confirmed the math based on earlier models. There is all sorts of cool stuff that happens to a planet with these characteristics, depending on where the torus you are and how it is tilted relative to the plane of its orbit around the star. You can even get all sorts of stable moon orbits passing through the hole in the middle. If you want to keep it a little closer to your original idea, you can have it be a circumbinary planet (it orbits two stars, which orbit each other. It goes in a circle around the pair, not a figure 8 between them). A few moons can reflect light on other parts of the planet too (+1 to the answer that mentioned tons of moons). Check out the link above. I've included a couple of the pictures from that page, but the full article mentions a ton of cool properties of a toroidal planet, including how it would be lit by its sun.

To tie it back to your original question, if the "day" of the toroidal planet and the "year" aren't a multiple of each other (Earth isn't either, but its close enough to fool people without accurate measurements), you could make predicting when a region gets sunlight very difficult for a culture that doesn't have a strong grasp of trigonometry.

light being cast on a toroidal planet as it orbits a star Light being cast on a toroidal planet as it orbits a star.

an example of a crazy moon orbit around a toroidal planet.  This is one of many stable orbits. An example of a crazy moon orbit around a toroidal planet. This is one of many stable orbits.

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Artificial Suns.

Your world does not actually have a "sun" as we think of one. It does not orbit. It flies through the interstellar void with multiple, gigantic fusion reactors in orbit of it.

The reactors are ancient, and not in the best repair (since everyone on the planet has forgotten that they are constructs and nobody does maintenance any more.) so the intensity and colour of each can be variable.

The suns could double as the planet's propulsion devices, varying their output and orbits in ways that slowly direct the planet toward whatever its ultimate goal is. This could easily include turning the entire reactor on and off. Especially if each reactor, in addition to providing light and warmth to the planet's surface, has some kind of gravity generator it can use to change whether it's pulling the planet or being pulled by it as it orbits.

This would work best if the world is at least semi-hollow to reduce mass, so now you have an excuse for why the "underdark" even exists. Probably it was hollowed out for material to use to build the reactors and the dross was dumped overboard to reduce mass.

Now you can have plots about "suns" going dark and not coming back, which can either be due to malfunction or due to the "worldship" nearing its destination. You can have plots about the new sun that has appeared in the sky that is more constant and stable than the others and the natives trying to figure out what it means. (Especially where there are probably lots of ancient "prophecies" about it.)

Depending on what you have for "magic" in your fantasy setting, it could be the remnants of the brain-scanning control system for the ship coupled with the powerful and precise gravity and power generators in the "suns". "Magicians" could find their power waxing and waning depending on how well "attuned" they are to the particular "sun" in the sky at the moment. Magic wands and whatnot could be special-purpose control devices that even people who's brains aren't recognized by the system can use.

There are lots of directions you could go from here. Let me know if you want more. :)

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I don't want to be a spoiler, but if the pattern of day and night changes only a tiny bit, the effects on weather and climate are huge. Live on earth took several billion years of a relatively stable climate to develop. Or at least a climate that took hundreds of million years for each major change.

Your world would be uninhabitable. Not much fun for fantasy :-)

Also, your question sounds like asked by Ptolemy. Now we know that the sun is not an object that circles around the earth, coming "up" and going "down", but that rather the earth circles, along with the other planets, around the sun. A planetary system with more suns is possible, but even then, those suns do not really circle around your planet...

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    $\begingroup$ Are you sure the effects on weather and climate would be huge? From what people seemed to say on my other post concerning the consequences of this phenomenon, a day with no sun once in a while would not have important consequences, if energy redistribution is effective. Also, you have to consider that the phenomenon can start occurring after life has evolved on the planet if it was created artificially. $\endgroup$ – Dzarak Mar 28 '17 at 15:58
  • $\begingroup$ Concerning the way my question was asked, I am looking for an observable effect from the perspective of people on this planet, so it does not really matter how the solar system is configured, as long as it works and it is stable. $\endgroup$ – Dzarak Mar 28 '17 at 16:00
  • $\begingroup$ Here is my other post I was mentioning: worldbuilding.stackexchange.com/questions/75465/… $\endgroup$ – Dzarak Mar 28 '17 at 16:05
  • $\begingroup$ @Dzarak Sure, huge. Some CO2 in the athmosphere and we get hurricanes, droughts etc. From week to week the sun gets up a few degrees higher and we experience the end of winter. etc etc. With a few suns more or less the diferences will be orders of magnitude greater. Not to mention the effects on humans (and other species) of changing day/night patterns. Over millions of years species got adapted to some patterns, so better don't make big changes in another fantasy world. $\endgroup$ – Roland Mar 29 '17 at 20:00
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    $\begingroup$ Good luck! On a side note, with just one sun, imagine breaking a tiny piece of it and throwing this at earth: carrington event 1859, real fun! $\endgroup$ – Roland Mar 29 '17 at 21:35
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If it's a fantasy world, you could have a number of different actual suns in different solar systems which the planet shifts between. The suns have identical masses (including a "missing" sun which radiates either magical "dark light" or just in a spectrum which makes it look like night to people with regular vision) and the planet's orbit is identical in each system. There could be equivalent planets with identical relative orbits (and even exact positions within their orbits) in the "other" systems and they just swap, instantly and magically, on a periodic basis. This would be similar to Piers Anthony's Apprentice Adept series, where a few people could move/swap between "two worlds occupying the same space in two different dimensional planes" (https://en.wikipedia.org/wiki/Apprentice_Adept). You could define any rules for operation for these transfers you want, such as:

  • stable multi-dimensional-plane space manifold rotates around all the suns, and has "slots" (like a cheese grater's blades) for shifting planets between the dimensions.
  • giant space octopus was created by a more-multiplanar Creator than anyone could have ever imagined, and has been tasked with shifting the planets between dimensions for eternity, but every once in a while it forgets where it is in the shift cycle and just restarts at the top of the chart; perhaps that's the dark sun. Or perhaps the giant space octopus has a complicated holiday schedule it keeps exactly as The Creator dictated it.
  • wormholes make the orbital paths around different suns connected. Wormholes are for some reason attached to the suns (the work of a very large Creator, either fantastical or scientific) and the wormholes work in pairs (or higher-order groups) to shuffle planets around between suns in different places, and the arrangement of planets on orbits is such that things are gravitationally stable. Diagram shows a minimal example of orbits divided into portions which go around solar systems in very different places. Segments are approximately one day long and an unexpected visit to the "dark sun" happens when one of the wormhole pairs twitches.

This last arrangement could have been created for any number of purposes, but one possibility is that some advanced entity/group tracks down habitable planets which are going to be destroyed by orbital problems and finds it far easier to move them great distances via wormholes than to recreate such a habitable planet and, not wanting them wasted, has assembled them into this livable holding pattern which:

  1. can be expanded relatively easily to accept more planets as they are found,
  2. distributes the gravitational effects so they're stable,
  3. serves as a convenient interchange between different parts of the/a/more-than-one galaxy (so you'd get lots of "shooting stars" which are actually shiny Creator race spacecraft zipping by), and
  4. enhances the development of intelligence on the planets by a regularly-scheduled shift in which sun comes up. (I am unable to find a reference, but this is a theory that our moon gave rise to advanced intelligence by creating an evolutionary advantage of the ability to plan hunts into the future as the lunar illumination regularly varied. No doubt if that's true there were some hungry packs of animals during some lunar eclipses...)

In option #4 we also find the suns are all about the same mass because it was easiest also for the Creators in question to just locate useful suns (perhaps they're not rare in the slightest) for this project, and the orbits are sliced with wormholes while the suns remain in their original locations because there's no advantage to moving the suns with wormholes (for one thing, where would you move them to?), or else there are technical restrictions making it inconvenient. (And the planets aren't placed into orbits without wormholes because dealing with a planet's relative velocity on initial capture is quite involved, and requires the use of many wormwholes; needing to keep those around for repeat use, they are built into the storage arrangement. Capturing a new planet or adding a loop around another star would be a dramatic event indeed to everyone on the planets involved, but hopefully rare.)

orbits around distant suns are "spiral bound" via wormholes attached to host stars

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  • $\begingroup$ Even though I didn't choose your answer, I like it, and it would kind of fit with the setting I currently have, so I might use some parts of it in some way. Thanks for the idea! $\endgroup$ – Dzarak Mar 30 '17 at 17:52
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Option 1: Irregular planet shape

Well, it is not physically realistic, but:

I think it would make a really interesting setting to have your planet orbit multiple stars, but have the planet not be spherical. Instead, it could be some odd shape such that at any given time at any point on the planet only 1-2 suns (or sometimes none) were visible, the rest being obscured by the planets odd shape. This could also lead to an interesting variety of settings on the planet, e.g. harsh desert regions where many suns were always visible, or cold regions that were always in darkness.

This made for an interesting setting on the planet of Prester in Last Exile (which is what I was thinking of when I posted this). There, the shape of the planet drove much of the mystery of the plot and had a large impact on the general development path of that society.

I'm not entirely how the planet should be shaped, I can conceive of shapes for 2 or 3 suns but not sure about 12 (you'd have to draw some diagrams to figure it out).


Option 2: Hollow planet with holes

Another option could be a spherical, hollow world, probably artificially created, where most inhabitants live on the inside, with but large (possibly intentional) holes in the sphere. Then as the planet rotates, different suns would be visible through different holes depending on your location in the planet.

This option is probably slightly more scientifically explainable (to some extent) than the odd-shaped planet, although personally I like weird shaped planets for the fantasy aspect.


Option 3: Non-circular orbit around multiple stars

A third option, although I do not know if it is possible, but if it is it is potentially the most realistic, is to have multiple stars clustered together and the planet switches between them, weaving a path through the stars rather than having a circular orbit.

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Perhaps your people are actually experiencing something like The Truman Show or The Matrix.

They are in either a controlled environment, or a virtual one and whoever put them there controls the heat and illumination of their world.

This could be a plot twist that is revealed in the end or a "secret" between the author and the reader that the story characters don't know and may never find out.

There could be cults that claim they found out and create various, even conflicting, religions based on just what little insight they may have to this truth.

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  • $\begingroup$ This was what I was thinking. Trapped in a VR fantasy sword and sorcery world. $\endgroup$ – Thorne Apr 4 '17 at 4:07

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