# Could you see the other side of a Dyson Sphere with a radius of 1AU?

Asked by mrentropy (17168) August 4th, 2009

Here’s some theoretical thinking for everyone.
I want to create a Dyson Sphere with a radius of 1 AU.
Being a super being of some kind, I manage to make it stable and add some gravity so that people could live on the inside of the shell.

So, my question is: If someone were standing on the inside of this shell and they looked into the sky, would they be able to see the other side of this sphere? If it were a clear day and the entire inside of the shell were covered with, say, various flora and cities of a modern Earth, what would it look like from the other side of the shell?

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I doubt it. The sun would get in the way. Also, even if there were no sun at the center, the atmosphere would be deep enough to scatter all light coming from the other side. It would probably just look blue. It would be like earth, except the horizon would go up instead of down. It would be like always having mountains in the distance.

wundayatta (58492)

I think you would see the other side if there was no sun in the middle. No idea what it would look like though.

btko (2806)

i don’t think you would.
look at the sky on a sunny day. do you see the stars? No you don’t. the athomsphere together with overexposure from the sun , prevents it. in a dyson sphere the light would have to go through twice the amount of atmosphere.

ragingloli (40259)

I had thought about the atmosphere and it’s affects, but I wasn’t sure how much of a difference it would make. I can’t see stars during the day, but the stars aren’t bright enough to overcome the ambient light of the sun. In a sphere, however, all points on the inside of the sphere would receive the same amount of sunlight.

I suppose I could make a sun shade that would create an eclipse of sorts to create a night time on a portion of the sphere. That should make it easier to see the other side.

mrentropy (17168)

@mrentropy
I figure that if you could eclipse the sun to cast a shadow on one region of the sphere, from that point of view, the entire sky would have the appearance of a full moon. The reflecting surface would be much more distant (2 AU instead of 0.00257 AU), but since it would fill the entire sky, I wonder if that would matter.

Fyrius (14525)

Don’t forget to wear your protective glasses, though.

mattbrowne (31537)

No, I think the atmospheric haze would obscure any detail beyond a certain distance from any given point on the sphere.

At 1 AU the whole thing is going to get pretty hot, since there is nowhere for the sun’s heat to go, except by conduction through the shell into space on the other side. Its going to heat up like an oven; so you might have to enlarge the sphere so that you have a greater surface across which you can dissipate the heat. If the shell is only 3 meters thick, you would have to spin it pretty fast to create sufficient centrifugal force to compensate for gravity, which you will need and to keep the atmosphere close to the sphere, since the shell won’t have enough mass to be able to do so by itself. In a sphere with an energy source in the middle, you are going to have significant amounts of energy being reflected back toward the sun. This is going to “bunch” up at various strata where there are various chemical reactions and interaction effects.

If the atmosphere is to sustain terrestrial life, there will be have to be sufficient water vapor to compensate for the lack of oceans. There will have to be clouds and, no doubt, some dust and pollution. The tidal motion of the moon and the planets will introduce chaotic effects into this atmosphere. These will stabilize at certain altitudes above the sphere creating phase transition zones, marked by things like reflective cloud layers, jet streams, plasma belts, aurora borealis-type effects, and possibly other magnetic and radiation belt phenomena, all of which will refract and diffuse the sun’s radiation into some kind of haze, the way our blue sky is now, only it wouldn’t necessarily be blue, and it could be much brighter or much darker, depending on the composition of the atmosphere and the final amount of particulate matter and how reflective the water turns out to be in a spherical system.

Because you have no gravity to speak of, and therefore no oceans, you may have to have a thicker layer of atmosphere than you do on Earth to make the weather system work. The thicker the atmosphere, the less you will be able to see. Because the sphere is so many times larger than Earth, its curvature will appear correspondingly less. Everything will appear totally flat, since the apparent horizon won’t achieve a noticeable elevation until several several thousand miles away. At that distance, the horizon will very likely be obscured by atmospheric haze, clouds and glare. In fact, the horizons might even appear dim or dark, because you are looking at clouds edge-on through a thick mass of gas, vapor and particles; and also because the energy they are receiving from the sun is being reflected back toward the sun at around 90 degrees relative to the viewer. If the cloud cover is very thick, the “horizon” may actually be provided by the atmosphere, rather than the sphere. In other words, inside the Dyson sphere will be layers of slightly smaller spheres, that consist of various strata of the atmosphere. I imagine that it would be like looking at the underside of thunder clouds, going off in all directions. The only apparent variation in altitude will be the atmosphere, since the sphere will be uniform and very flat-looking because of the very slight curvature.

The actual diameter of the sphere will almost certainly not be 1 AU, but another value determined by the gravitational properties of the sphere and its atmosphere, and all the other mass in the solar system. The orbits of the planets are determined by certain harmonic ratios . Moving that much mass out of the planar orbits that the planets now occupy and redistributing into in a sphere, will almost certainly require significant adjustments to the orbits of all the other planets, or it could kick loose all kinds of pesky asteroids that are currently held in place through the gravitational tides of the planets, and they could come crashing through the sphere.

In fact, there is probably only one diameter that will be sufficiently large to dissipate enough solar radiation so that temperatures are within life-sustaining ranges, and still small enough to cover with a life-sustaining atmosphere, soil and water. Indeed, there might not be a diameter that can meet these all of these conditions, given the amount and type of material we have to work with in our solar system. Anyway, the larger the actual diameter, the further away everything is and the more atmosphere there is to obscure it. In a shell only 3 meters thick, it is not as though you are going to have huge mountian ranges or any other features that will be visible at a distance; so most of what you will be able to see will likely be fairly close.

Zuma (5908)

@MontyZuma Your discussion made me think about some other things that happen if you are rotating a sphere. The closer you got to the poles of the sphere, the less centrifugal force there will be, so that near the poles you’d pretty much be floating in air, and a lot of people would probably get easily lost floating up into the atmosphere and never being found again.

Under such circumstances, it seems like it would be better to have a ribbon of material around the sun, instead of a sphere, as in Larry Niven’s Ringworld (which, despite it’s popularity, is one of the very very few series of books that I could not finish).

wundayatta (58492)

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