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I am working on a roleplaying campaign guide set inside a Dyson Sphere. It's a solid shell around a star like our own and is 300 million kilometers across centered on the star. The atmosphere hugs the inside of the shell and is several thousand kilometers thick.

I am really trying to wrap my head around what the average person standing on the inside surface would see if he looked up. Anywhere he stands the star is as bright as our own but there is a night period when the light from the star dims down to about the brightness of our full moon.

I can't quite figure out how the atmosphere would affect looking across to a distant point elsewhere on the shell surface. I get as far as imagining the surface sweeping away and up in all directions and that the sun would block your sight looking straight up and around its blazing orb.

I hope this question isn't too off-the-wall, it's about as hard to describe as it is to imagine.

--edits---

To Mark Beadles, thanks for the comment, but since I designed this one, I set it so there is a constant 1G gravitational force pulling people to the inside surface of the dyson. The gravity stays constant all the way out to the outer layer of the sphere, there are 5 or 6 "layers" that make up the sphere itself. The gravity extends up to about 40,000 km above the inside surface.

Dungarth, to put it simply, living on the outside of a planet or sphere is stupid. If it's "designed" intelligently, all your protection from stuff like asteroids, gamma bursts, supernovae, etc, is in putting a tough barrier between yourself and the cold harsh universe. Of course, a LONG time has passed since people started moving in, and advanced as it is, strange things can happen over time to even the best machines.

So for those nice enough to drop comments on me, the sphere I am envisioning in is designed using tech that we haven't come up with yet. It compensates for many of the weaknesses seen in a solid shell in order to provide a safe living envronment for its residents, for whatever alien agenda the builders were following.

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  • Hmm.. This is asking about sci-fi physics, but for a roleplaying game. Perhaps it would be better on rpg.SE? – Izkata Jul 26 '12 at 0:25
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    @Izkata: ask yourself would a sci-fi expert give a better answer to this question than a RPG expert?. If yes, then this question belongs here. If not, then it belongs to RPG.se. Personally, I think it belongs here -- the RPG aspect could be omitted and the question would remain the same. – Sardathrion Jul 26 '12 at 7:20
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    Or, as the OP is asking about some material he's about to write, how about Writers.SE? But no, I think this a good place for it. – Mr Lister Jul 26 '12 at 7:45
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    Since this is for an RPG, I'll also point out the likely-obvious fact that a night sky would have no stars -- which historically have been a key source of religion and mythology on human cultures, but would be non-existant in your world. – KutuluMike Jul 26 '12 at 18:18
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    If you want a several-thousand-kilometer thick atmosphere, you'll need something other than gravity holding it there, unless you're willing to accept a surface pressure that's totally nuts. 1000 km is about the depth you have to go into Jupiter in order to get metallic hydrogen. – Micah Jul 27 '12 at 0:31
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This is covered completely in this Dyson FAQ. Basically, the ground looks even flatter than our own, but the atmosphere gives you a distant cloudy horizon. And the sky is very bright, though you can't make out many individual features:

What would a Dyson Sphere look like from the inside?

The curvature of the "ground" would be even less than on Earth, so to an observer close to it it would look perfectly flat. In a solid dyson sphere with atmosphere, the atmosphere would limit the range of sight due to its opacity, and the horizon would be slightly misty. The sky would be filled with the surface of the sphere, giving the impression of a huge bowl over a flat earth, covered with clouds, continents and oceans although for a real Dyson shell these would have to be immense to be noticeable....

It should be noted (as Richard Treitel has pointed out) that even a very dark surface will shine intensely, making the sky much brighter than on Earth. The albedo of Earth is around 0.37, so an interior with an earthlike environment would have a sky where each patch reflects a noticeable fraction of the sunlight.

In a type I dyson sphere roughly the same things would be seen: a plane wall of orbital habitats, solar collectors and whatnot stretching away into what looks like infinity (although here the curvature may become noticeable for observant viewers) and a hemispherical bowl covering the rest of the sky, centered around the sun. Solar collectors would have a very low albedo, but it is still likely that the interior will be very bright.

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    That is AWESOME, thanks for the link, it's a BIG help in letting me design the societies that live there, gives me a real feeling for what you would actually experience, thanks! – Ronald Stepp Jul 26 '12 at 22:14
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Bear in mind that you cannot actually stand on the inside of a Dyson Sphere, you would be pulled by gravity to the star in the centre (Since being inside a spherical shell you experience no net gravity from the shell itself.). You could walk on the outside of the sphere, if you had an outer shell to keep the air in and an inner shell to walk on.

If the spherical shell was spinning fast enough, I suppose you could stand on it. Then you would get interesting Coriolis forces inside the sphere.

This would mean you could walk around the equator and up to a certain point, beyond that you would be pulled off the sphere and float away into space. The habitable zone would be a wide ring around the equator. Since a Dyson sphere is so huge, you might not notice this from a point in the habitable band, since haze/mist etc would limit visibility to a few 100km at most; you wouldn't be able to see the sphere rising up around you unless there was virtually no atmosphere (300 million km is a LOT of air.)

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    So you're suggesting they use a Niven Ring instead? – Mr Lister Jul 26 '12 at 13:23
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    It is generally assumed that a solid sphere with an interior living space has gravity generators or somesuch to take care of this issue. When you are presuming unreasonable technologies in the first place why stop at one? – dmckee Jul 26 '12 at 14:58
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    Sorry for bringing actual physics into it... Gravity generators etc wouldn't work unless they did something other than create gravity, as the gravity pulling you to the outside would be balanced by the gravity pulling you to the far side, by the inverse square law. The contribution from the further away (but huge) segment of sphere above you cancels out the closer (but tiny) segment beneath you. – Nick Jul 26 '12 at 15:35
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    @MarkBeadles This is very true. You could have quite a cool campaign setting on such a sphere, with the protagonists able to transfer between orbiting platforms as they pass each other. It would be quite different to the one proposed by the question though. – Nick Jul 26 '12 at 15:45
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    @Beta: People assume a Dyson sphere needs to have a radius equal to Earth's orbit around the sun so that the amount of energy received per square meter is the same as that received on Earth. This is only necessary if you live on the inside and wish to have earthlike vegetation. If you lived on the outside, you could build a smaller sphere at exactly the right distance so that the gravity would be equal to Earth's while still capturing 100% of the sun's energy. – Dungarth Jul 27 '12 at 14:24

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