What would a dyson sphere look like . . .

[Forbin]

That doesn't ring true somehow. The whole inner surface is perfectly evenly lit. Even if the opposite side is 186 million miles away and lost in the glare of the star, it's still well-lit.

Though I imagine all detail will blend together at that distance. The opposite surface might look like a smooth, even color

 

[Jadzia]

Unlike earth, the curvature is upward, rather than downward, so you certainly wouldn't have an horizon. But how far could you see?

Well when you look into the sky at night, you are looking through an atmosphere, which is fairly transparent. Even with haze, you get plenty of light.

In a Dyson sphere, you'd be looking through two atmopsheres, which isn't so different. So in theory, yes you would be able to see other parts of the sphere.

Second question is illumination. Are the distant parts of the sphere bright enough to see?

Well, all parts of the sphere receive a uniform level of illumination from the star.

So all surface elements reflect the same amount of light.

Now suppose these reflections are diffuse. This means that reflected light is evenly in any reflected direction.

Compare two surface elements - one twice as far away as the other. The surface element twice as far away appears 1/4 area, and its light is spread inverse square, so reflects 1/4 as much light to you, the observer.

However, this lesser area is compensated for by the fact that the Dyson sphere is continuous, so distant parts of the sphere appear as bright a those nearby.

Looking at low angles does mean that light is travelling through more atmosphere, so there is more hazing.

Overall, looking up, you see the star directly overhead, and around it you see the far side of the sphere, reflecting as bright as the ground you stand on looking down.

Looking at lower angles, you see layer of haze, where the view may be fuzzy or grayer or duller compared to what is nearby. Looking over that haze, you see a wall in the distance, like mountains pushing up through the clouds - except that this is far side of the sphere extending up towards the star, again appearing just as bright as the land beneath your feet.

I hope that helps you visualise it.

 

[BolianAuthor]

Unlike earth, the curvature is upward, rather than downward, so you certainly wouldn't have an horizon. But how far could you see?

Well when you look into the sky at night, you are looking through an atmosphere, which is fairly transparent. Even with haze, you get plenty of light.

In a Dyson sphere, you'd be looking through two atmopsheres, which isn't so different. So in theory, yes you would be able to see other parts of the sphere.

Second question is illumination. Are the distant parts of the sphere bright enough to see?

Well, all parts of the sphere receive a uniform level of illumination from the star.

So all surface elements reflect the same amount of light.

Now suppose these reflections are diffuse. This means that reflected light is evenly in any reflected direction.

Compare two surface elements - one twice as far away as the other. The surface element twice as far away appears 1/4 area, and its light is spread inverse square, so reflects 1/4 as much light to you, the observer.

However, this lesser area is compensated for by the fact that the Dyson sphere is continuous, so distant parts of the sphere appear as bright a those nearby.

Looking at low angles does mean that light is travelling through more atmosphere, so there is more hazing.

Overall, looking up, you see the star directly overhead, and around it you see the far side of the sphere, reflecting as bright as the ground you stand on looking down.

Looking at lower angles, you see layer of haze, where the view may be fuzzy or grayer or duller compared to what is nearby. Looking over that haze, you see a wall in the distance, like mountains pushing up through the clouds - except that this is far side of the sphere extending up towards the star, again appearing just as bright as the land beneath your feet.

I hope that helps you visualise it.

No. The curvature is meaningless... it is the distance that is the issue... we're talking about "ground" that is still roughly 93 million miles away from a star. There WOULD be a horizon. In this case, it would be the vanishing point of what is intelligible, before being absorbed by atmospheric haze.

The edges of the sphere WOULD look like one solid colored wall, but ONLY an extremely small portion of the far wall, if any, would EVER be visible. For one, the distance to the far edge is so vast, that your view of what little of it you could see, would disappear into the sky almost the instant your eyes leave ground level, or the horizon line.

Two... the night sky... you would NEVER be able to see the "upper" wall of the sphere, for two reasons... one, during "day" (if day is not perpetual), you would not be able to see anything, due to the light of the sun. If there were such a thing as night, all you would ever see is a perfectly dark sky, because consider that not only are YOU 93 million miles from the sun... but then it's ANOTHER 93 million miles from the sun to the upper hemisphere... thus, it would be so far and dark, that nothing but darkness would ever be intelligible.

 

[David cgc]

Two... the night sky... you would NEVER be able to see the "upper" wall of the sphere, for two reasons... one, during "day" (if day is not perpetual), you would not be able to see anything, due to the light of the sun.

Well, that depends on how bright the lit surface is, and the thickness of the atmosphere. If it's the light from the surface is strong enough to be brighter than the sky, than you could see it, just like you can see the lit side of the moon in the daytime, but the dark side is overpowered by the blue.

If there were such a thing as night, all you would ever see is a perfectly dark sky, because consider that not only are YOU 93 million miles from the sun... but then it's ANOTHER 93 million miles from the sun to the upper hemisphere... thus, it would be so far and dark, that nothing but darkness would ever be intelligible.

Why would it be dark? We can see things much farther than 93 million miles in the night sky lit only by the sun, such as Jupiter. And the sphere would, by definition, take up the whole sky. Imagine if the entire sky was as bright as Jupiter, not just a tiny point. Indeed, I'd guess an artificial night would need to block out the whole sky, not just the sun, because of how bright the reflected light from the daytime portions of the sphere would be. Or it would have to affect the entire sphere at once, not just part of it.

 

[BolianAuthor]

^

But you all are forgetting the very nature of the Dyson Sphere itself... the star is CENTRAL in the Sphere. THUS, you CANNOT see the other hemisphere, because to do so, you have to somehow look PAST the brightness of the sun itself, which we cannot do... have you ever looked up into the sky, and been able to discern anything of substance, when the sun was right in your path of view? You may be able to discern very little, but you cannot make much out of anything. PLUS, as we have discussed, if you're talking about the other side being equal distance from that sun as we are, that's like trying to see another planet, on the other side of the sun, whilst looking at the sun. It can't be done.

That's like saying if the Earth were curved in a similar fashion, that you would be able to discern the Himalyas from Central park, in NYC... that's absolutely absurd, because the sheer distance involved is too great. You might be able to make out the very rough features of the region, as if you were looking at that continent from space, but you would not be able to see much more than that, if even that, given the illusion of sky as interference.

 

[JuanBolio]

the sun wouldn't move across the sky . . . imagine continuous noon!
how would the natives measure the passage of time?

I'm gonna take a guess that in these cultures some sort of clock of time-keeping device gets invented earlier than one in a place with more normal day-night cycles.

Yeah, you'd think a race capable of building a Dyson Sphere would have little trouble with digital watches...

 

[Ziz]

I'd go with the arrangement familiar from Niven's Ringworld: have two concentric spheres. The outer one would be this Trek construct which provides habitable area at about 1 AU radius. The inner one would be a more accurate Dysonian construct where giant solar energy collectors orbit the central star, eclipsing it at regular intervals to create swaths of night on the surface of the outer shell.

Ok, wait a minute. I get the idea of something eclipsing the sun every now and then to create a period of artificial night time, but that sounds like a very 2D solution, in the most literal sense.

If this "blocker object" is essentially in orbit around the sun within the sphere in the same fashion that a starship orbits a planet, how is it going to block the sun out for the parts of the sphere at the top, bottom, or other angles? You'd have to have a bunch of them orbiting the sun, creating these little eclipses all over the inner surface of the sphere, so each "patch" of surface - say a few hundred miles each - would have its own day/night schedule, similar to Earth time zones.

 

[Maurice]

Also, I think that the eclipsed areas of the sphere would still be bathed in quite a bit of light, reflected from other portions of the sphere.

To get an idea of that, would any of the resident 3D artists be able to render a quick&dirty image showing the following? Or would that be too much to ask?

* A spherical object with a diameter of about 2AU, with the camera placed inside and at "ground level".
* Views might be: looking straight up, straight up with the sun completely shielded by an object, looking towards the horizon
* One light source in the center of the sphere, light quality and quantity equaling that of our sun.
* Texture of the sphere: some random earth surface imagery, with diffuse reflection set to about 35%.

Looking straight up, with the sun shielded, you know what you'd see? Nothing. You'd see a featureless "sky". Even if there was no atmosphere, you couldn't see anything but an endless flat color.

I made the following image to crudely illustrate why this is:

CLICK TO SEE IN DETAIL
​

The math is crude, so dismiss it, but the point still stands.

As you can see, even at twice the distance to the Moon only the most gigantic details would be visble (continents), and by the time you cross into the millions of miles, all detail would vanish (to the naked eye). The next step beyond this illustration would be a field of view 80 million miles wide and from an distance of 40 million miles, at which distance, to be visible, features would have to be a minimum of hundreds of thousands of kilometers across...and that's still less than half an A.U.! The far side of the sphere would be almost five times that distance.

 

[David cgc]

If this "blocker object" is essentially in orbit around the sun within the sphere in the same fashion that a starship orbits a planet, how is it going to block the sun out for the parts of the sphere at the top, bottom, or other angles? You'd have to have a bunch of them orbiting the sun, creating these little eclipses all over the inner surface of the sphere, so each "patch" of surface - say a few hundred miles each - would have its own day/night schedule, similar to Earth time zones.

Well, it could be a half-sphere, considerably greater in size than the sun. Or a cluster of objects arranged in a similar fashion. At first I thought a giant orbiting shell for the sun would be a bit much, but then I remembered, hey, its in a Dyson Sphere. They can build anything they want as big as they want.

 

[BolianAuthor]

If this "blocker object" is essentially in orbit around the sun within the sphere in the same fashion that a starship orbits a planet, how is it going to block the sun out for the parts of the sphere at the top, bottom, or other angles? You'd have to have a bunch of them orbiting the sun, creating these little eclipses all over the inner surface of the sphere, so each "patch" of surface - say a few hundred miles each - would have its own day/night schedule, similar to Earth time zones.

Well, it could be a half-sphere, considerably greater in size than the sun. Or a cluster of objects arranged in a similar fashion. At first I thought a giant orbiting shell for the sun would be a bit much, but then I remembered, hey, its in a Dyson Sphere. They can build anything they want as big as they want.

Like DS9Sega has said... "even at twice the distance to the Moon only the most gigantic details would be visble (continents), and by the time you cross into the millions of miles, all detail would vanish (to the naked eye)". This is absolutely true.

So there is NO way a series of eclipses a mere few hundred miles in diameter would do anything of substance... you are talking about a SPHERE that is as wide as Earth's orbit around Sol... over 93 MILLION miles, in EVERY direction... those small eclipses would be like nothing more than pencilpoint blips, if even that.

 

[Bacl]

I really wish more "science fiction" (i.e. scientific fiction) had been explored in Star Trek. After you get the setup of the world and its tech abilities, very little along the lines of "dyson spheres" and other theory was used.

A real shame.

 

[Timo]

So there is NO way a series of eclipses a mere few hundred miles in diameter would do anything of substance.

I don't quite understand. Surely they would create a sequence of nights and days for the hundred-mile area in question? Why is that "not of substance"?

Although actually, a hundred miles of night sounds pretty unlikely. The penumbra of a hundred-mile shadow disk at the distance of one AU would be something like ten times the star's diameter if the disk orbited the star at about 0.1 AU, right?

The visuals of "Relics" shouldn't affect this one way or the other. We never saw enough of the inner surface to conclusively disprove the idea of local nights, and when the ship orbited the star, she could have been inside the orbital radii of the shadow disks and consequently the camera would have been unable to see any of them.

Timo Saloniemi

 

[Cid Highwind]

...because locally eclipsing the star itself may not be enough, if behind that star is a huge silver screen, filling the whole sky and reflecting a considerable amount of light.

As DS9Sega pointed out, an observer may not be able to make out any surface details, but the amount of light would still be there. After all, that's exactly what this sphere is supposed to do - collect and retain all of the star's energy.

 

[Timo]

I know the general albedo is a problem, but I'd still accept the penumbra of the shadow disk as "night". After all, where I live, the nights never get really dark for one third of the year (unless it's very cloudy all the way to the horizon and a bit beyond), and they still serve an important biological role.

Speaking of clouds, it might be that controlled cloud patterns or other close-to-surface filter devices would be used for creating the night conditions, either for the biological purpose, or as a side product of the process that collects most of the starlight.

Timo Saloniemi

 

[Meredith]

What would it look like inside of a dyson sphere built around a red dwarf?

There would be greater curvature.

 

[Forbin]

This made me start reading Ringworld again.

 

[Brian]

LOL, it's making me think of picking up Rendezvous With Rama again. Rama at least has curvature small enough for we puny humans to visualize.

 

[Meredith]

Could a 3-D rendering engine even handle the immense distances and light distances involved in rendering a view inside of a dyson sphere or would it take a super computer a year to render it correctly with all of the atmospheric effects and inner wall effects and shadow square effects.

 

[backstept]

I was able to draw out a few circles in AutoCAD to demonstrate the distances involved . . . didn't save the drawing, but I would assume that a 3D program could handle it
the tough part would be making the 'sun' light source with the right falloff and magnitude, and the atmospheric shader

 

[Christopher]

Yes, Dyson's original idea involved, IIRC, a series of habitable platforms surrounding the central star, not a solid sphere.

Actually his original proposal was a cloud of solar-power collectors surrounding the star. He was thinking about a way to harness all of a star's power, not to create an artificial habitat. Basically, it was SF writers who extrapolated it into a habitat and misinterpreted it as a solid sphere.

Create night with the correct size object(s) orbiting closer to the sun.

Why? The sun would be a limitless supply of energy. Crops growing non-stop, energy flowing through photovoltaic cells powering homes and industry. Just have really, REALLY good blinds in your home or maybe their people got used to sleeping in the light of perpetual noon.

Heat builds up. I'd think it would be a good idea for a lot of things, whether living organisms or artificial structures, if they occasionally got a respite from direct sunlight and a chance to cool off.

Of course, that's the problem with a solid Dyson shell to begin with -- not only do you have heat accumulating, but you have the stellar wind building up inside. A solid DS would be a pressure cooker, unless it was built with release valves for the hydrogen constantly blowing off from the star (and way of shunting it away from inhabited areas.

The other problem is that the gravity inside a uniform spherical shell is zero at any point. The inner surface would be weightless and everyone would fall into the star. And there'd be nothing to keep the star centered; if a big flare or something imparted a slight acceleration and pushed the star off center, there'd be no counterforce to stop the drift. The DS would need thrusters to keep station. (Although it's better off than a Ringworld, where any motion off center creates a force that pulls it further off-center until ka-doom.)

Who thick do you suppose the shell would have to be? Suppose there would be layers of the shell like a neutronium outer layer and a few dozen miles of silt, dirt and clay?

The amount of neutronium required to create a sphere of that volume would be prohibitive. In the novel Dyson Sphere, Zebrowski and Pellegrino asserted that a whole sector of space had been stripped of all planetary and subplanetary matter to create the Sphere's neutronium shell.

Realistically, why would you need something that dense? We're presumably talking about a membrane under tension (the tension coming from the Sun's light pressure and stellar-wind pressure), literally an inflated balloon. So what you need is tensile strength and flexibility, not bulk. It could be made of carbon-nanotube fabric, perhaps.

the sun wouldn't move across the sky . . . imagine continuous noon!
how would the natives measure the passage of time?

I'm gonna take a guess that in these cultures some sort of clock of time-keeping device gets invented earlier than one in a place with more normal day-night cycles.

Why would they need to invent anything? They live in a technological construct. Their ancestors probably invented watches millennia before they moved to the Dyson sphere.

But you all are forgetting the very nature of the Dyson Sphere itself... the star is CENTRAL in the Sphere. THUS, you CANNOT see the other hemisphere, because to do so, you have to somehow look PAST the brightness of the sun itself, which we cannot do... have you ever looked up into the sky, and been able to discern anything of substance, when the sun was right in your path of view?

Sure, if you're looking directly across, but what if you look off to the side, say, 45 degrees off the zenith? If it were a 1 AU-radius sphere around a Sunlike star, then that star would only subtend half a degree of arc in the sky. You've still got 179.5 degrees worth of sky to look at, all of which would be taken up with the surface of the sphere. Of course you couldn't see any detail, unless it had oceans millions of kilometers across, but you could see the surface, in theory. If you were, like, in a balloon high enough in the atmosphere that light scattering didn't get in the way.

What would it look like inside of a dyson sphere built around a red dwarf?

There would be greater curvature.

But still far too great to be discernible to the human eye or mind.