For my space-fantasy setting I'm considering using the concept of Hollow-Worlds.

I devised in-universe reasons for the presence of a day night and season cycle.

The Hollow-world's "Inner-sun" cycles on and off creating day for one hemisphere and night for the other and heat output cycles over months creating seasons

  • I Like, but am not sure of the idea of the world having seasonal quadrants. That is one fourth of the world always experiencing one of the seasons, in a kind of literal wheel of the seasons.

To get an equator and arctic I decided that heat wasn't evenly resealed by the "Inner-sun", some areas received significantly more or less heat than others?

I have a few questions related to my premise

  1. How would the world being on the inside of a sphere effect the climate?
  2. If the hollow world had seasonal quadrants,that is each quarter of the world experiencing one of the seasons. How would this effect the weather.
  3. Does my idea of the "Inner Sun" unevenly releasing heat, give a working alternative mechanism for an earth like climate?

I ask this question because I want to understand the logical consequence of my premises and to patch holes in it.

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    $\begingroup$ Have you looked up Dyson spheres and Dyson swarms? There is a lot of literature about them and they could give you good ideas. $\endgroup$
    – ThreeLifes
    Commented Apr 6, 2017 at 13:26
  • $\begingroup$ The concept of Flat Earths should be quite interesting or you. This is a video on how to construct a flat-earth megastructure, not about the nut jobs believing that Terra is flat. $\endgroup$ Commented Sep 12, 2019 at 15:45

5 Answers 5


You're going to have a problem with gravity.

The center of mass of a sphere is at it's center. As a rule of thumb if you are inside a uniformly dense shell the gravitational attraction of the shell cancels out. There is no way for people to stand and walk on the inside of the surface.

Spinning the sphere, hoping to create the illusion of gravity through centripetal force, would lead to non-uniform acceleration. As people traveled away from the equator towards the poles the outward force would decrease. Similarly the direction of the force would be constant while the surface normal (the direction upwards relative to the floor) would be changing.

The problems with rotational gravity could be avoided by switching to a cylindrical structure of constant radius. This would also allow for regions to be further away from your light source resulting in colder "polar regions".

  • $\begingroup$ While accurate, his question was relating to how to get different seasons on the inner surface. Not the gravity. $\endgroup$ Commented Apr 6, 2017 at 14:24
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    $\begingroup$ The question as currently worded just asks for holes in the concept - this is a fairly large one. I agree with you that it may not be what the question was intended to ask about though so mixed feelings from me. $\endgroup$
    – Tim B
    Commented Apr 6, 2017 at 14:25
  • $\begingroup$ @TimB I feel the same way, but without any other info on this world, I assumed the premise of his question was strictly related to getting seasons on the interior. Figured the OP had handwaved the rest and wanted a little realism. $\endgroup$ Commented Apr 6, 2017 at 14:29
  • $\begingroup$ @JoeKissling They asked for a reality check. There's a fundamental flaw in their base assumptions that they didn't handwave away. They asked about the logical consequences of their premise. Gravity is one of them. $\endgroup$
    – sphennings
    Commented Apr 6, 2017 at 14:34
  • $\begingroup$ @sphennings I do understand, Good edit. $\endgroup$ Commented Apr 6, 2017 at 14:40

You could make it so the inner sun is not on the perfect center of the sphere, but in a orbit that brings it closer to some parts (and further of others) as the year goes along. A slight change in the distance could be the difference between the temperature of the seasons thought you would need other factors for the changes in humidity and climate.

It is mechanically much simpler to explain than an internal working causing yearly variations of the suns output.

The orbit could be caused by a gravity influence from outside the sphere i.e.: the outer world's sun, tugging at it.

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    $\begingroup$ What would the inner sun be orbiting? $\endgroup$ Commented Apr 6, 2017 at 13:39
  • $\begingroup$ I was running entirely off the hollow-earth's idea of a stationary inner sun that hovered at the dead center of the sphere. Does the sun moving offer any benefits that the sun having a variable out put? $\endgroup$ Commented Apr 7, 2017 at 11:54

Maybe the "sun" is more like a spinning yin/yang symbol. Day/night would be if the light or dark side of the sun is facing you. You can then go two ways:

  1. Yang is stronger at the equator of the sun and yin is stronger at the poles. this makes it hotter at the equator if the hollow earth and colder at the poles. This makes it similar to Earth.
  2. Yin is stronger at one pole of the sun and yang is stronger at the other. In this scenario, on pole would be cold and the other would be hot/desert and the center would graduate from one to the other but generally be mild.

In either scenario, seasons could be handled by a cycle within the sun where either yin or yang would be stronger or closer to the surface at any given time.

  • $\begingroup$ That's almost what I was going for. The sun has a rhythm or beat. One side alight the other dark, with temperature variation of a course of several months(12) to create seasons. Energy not being evenly released would create climate zones like on earth. Would the world being on the inside of sphere radically effect the conditions? $\endgroup$ Commented Apr 7, 2017 at 12:58
  • $\begingroup$ From a science standpoint (which is already so far out the door it has a different postal code), the heat has to go somewhere. On Earth, the heat radiates off into space. In the hollow world, the heat has to first absorb into the rock floor. The decrease in solar heat needed to maintain a balance would even out the temperatures enough to reduce the effect of seasons. So, I would "magic" that. $\endgroup$
    – ShadoCat
    Commented Apr 7, 2017 at 15:48

You could get seasonal variations by varying the output of the inner star in quadrants. Or with slightly less handwaving you could use Sun Shades to block varying amounts of starlight to get your seasons. They could rotate around the star slowly to produce seasons. This method would also negate the need for the inner star to release uneven amounts of heat and the shades could be constructed to only block thermal so that there is no real change in the amount of light, only heat.

  • $\begingroup$ Would the world being on the inside of sphere radically effect the conditions? $\endgroup$ Commented Apr 7, 2017 at 13:13
  • $\begingroup$ @Trismegistus I focused on the specific case of your lighting question, doing what I described ought to create a climate indistinguishable from earth. Now there are other issues that I ignored like the gravity being zero on the inside, which would make living inside very challenging. $\endgroup$ Commented Apr 7, 2017 at 13:19
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    $\begingroup$ @Trismegistus - You need to keep in mind that, assuming the sun is at the center of the sphere, it is always high noon everywhere. So the only way to affect local temperature is to affect the amount of sunlight reaching the surface, and sun shades seem the best option. For that matter, you can have rotating belts of variable optical density, whose interactions provide the sort of long-term variations you need. Unless, of course, you just let your magic gravity generators have other effects as well. $\endgroup$ Commented Apr 7, 2017 at 14:56
  • $\begingroup$ @WhatRoughBeast I wouldn't need magic for the AG just a breakthrough in unified-field theory. If not mistaking you, then as long as the energy that the surface is receiving is distributed the same it is on earth, the actual shape of the world isn't a factor. $\endgroup$ Commented Apr 8, 2017 at 1:58

Instead of a traditional inner sun, I would suggest putting an artificial micro white hole. White holes are opposites of blackholes. (Forgive the scientific inaccuracies if any, ) Blackholes are basically extreme spacetime wells that cause everything to fall in it. So a white hole in this case, would be a space time peak. With negative gravity, it would push things away, allowing people to stand on the inner surface as acceleration due to gravity will be outwards from centre. It has to be extremely small in size to not blow apart the planet. For seasons, perhaps you can make the white hole oscillate or revolve around the center of the planet due to the unevenness of the planets shell Or maybe due to some other astronomical body revolving around the shell planet. And since it's a white hole, it gives light.

But there in lies a problem, what to do about day and night ? So another suggestion from me would be a paired micro blackhole and micro whitehole. They can revolve around each other like yin yang. The side with the blackhole will have night, the other side will be day. The plane of rotation has to be slightly off center in z axis and The axis of this revolution can probably tilt back and forth, like a spinning top, which should be able to give you seasons as well. Of course this makes gravity an issue. So perhaps a bigger white hole with a smaller companion blackhole ?


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