I hope this is focused enough: my question boils down to: "How do people living in a Stanford Torus experience the sky?"

Context: Operating on the assumption that we're in a fairly typical Stanford Torus (1.8km diameter, primary and secondary mirrors provide sunlight, mixed agricultural and living use around the rim as shown here: https://en.wikipedia.org/wiki/Stanford_torus), what would the 'daytime sky' look like to a person standing on the 'ground' inside the ring?

The interior illustration at the link above shows the sky/mirrors with a bluish tint, but I can't imagine why unless that's an effect of the glass used in the mirrors. The sun seen from space is just a blinding white sphere against black. Would it be likely that the mirrors would be treated somehow to soften/filter this effect both for human comfort and perhaps to create more optimal wavelengths of light for the crops?

Also for the comfort of the people living in this environment, would it be feasible/practical to create a day-night cycle by changing the position of the secondary mirrors / shutters (seen here: https://en.wikipedia.org/wiki/Stanford_torus#/media/File:Stanford_Torus_interior.jpg) so that the sunlight that the primary mirror bounces to the ring simply wouldn't be reflected in by the secondaries? Basically just shuttering the inhabited portions of the ring for the night? (I imagine it would be more energy-efficient to keep the dedicated growing portions of the ring lit at all times.)

Thanks in advance for any and all advice!

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    $\begingroup$ I'd love to have a crack at this but unfortunately I have to RTC, you're asking a lot more than one question here. $\endgroup$
    – Ash
    Jan 4, 2022 at 4:48
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    $\begingroup$ Hi, this is every broad. It might better serve you if you told us what you're aiming for, then we can help you get there - it's the way it works best here. Not an answer, but you can have pretty-much any lighting conditions that you wish, but it would depend partly on what's being orbited - i.e. would the torus be periodically in shade behind a planet or is it orbiting a star? If you want to block ultraviolet (because there's no ozone-layer like on Earth to do it for you) then the glass can do that - there's no reason for it to have a blue tint unless that's what you want. Can you edit. $\endgroup$ Jan 4, 2022 at 5:43
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    $\begingroup$ I love the Stanford Torus concept. I don't remember where I got this number but I believe the Torus "ring" only has a diamter of 130 M, that's not a whole lot of room for artificial sky. Do you intend to scale it up significantly? $\endgroup$
    – user93359
    Jan 4, 2022 at 5:48
  • $\begingroup$ @BeyondDisbelief there's at least 80000$m^2$ of transparent ceiling visible when you're standing in the centre of the tube (the exact number will be higher, but it is awkward to calculate so I won't). Plenty of view, certainly, though weather seems unlikely. $\endgroup$ Jan 4, 2022 at 19:40
  • $\begingroup$ The title is 1 question.. vote to reopen. There would be some kind of ceiling. It would depend on the proportions of the torus. When the ship diameter is huge and your torus relatively narrow, you'd see a near-straight tunnel and a ceiling above your head. When the torus is wide, the "ceiling" could be very far away. The Wiki example takes both worlds. The ship diameter is quite small, while the torus is relatively wide.. it exaggerates the curvature, the shape becomes exotic. In practice, they won't do that. The ship will be tunnel-like, I would expect. A large outer diameter, slow rotate. $\endgroup$
    – Goodies
    Jan 4, 2022 at 21:50

2 Answers 2


The drawing in your question is an accurate depiction of what it would look like, physically, from the inside. Their arrangement of mirrors, however, makes little sense.

The blue-sky coloring is synthetic Rayleigh scattering. Without it, the sun would be a harsh point in the sky, and the rest of the sky would be black. Real Rayleigh scattering takes place over miles of air, so the synthetic version would have to filter out some red and use tiny optical lenses to spread the light out.

For the day/night cycle, you'd want the mirrors to be independently rotating so that they rotate in a period one day less than the underlying torus. The initial calculations for the Stanford Torus had it spinning at 1 rpm to simulate gravity. The mirrors would need two characteristics:

  1. Curved so that the meters^2 of sunlight it intercepts is equivalent to the meters^2 of the ground it illuminates, and
  2. Has an increased sunlight in the middle, and reduced (and red tinted) in the morning and evening to properly stimulate our diurnal cycle.

Since most of the weight of the mirror would be on the daylight side, this would involve a counterweight on the night side. This shape makes a pretty picture in my head.


However You Want

Apologies if that sounds like a non-answer, but you're asking about an aspect of an entirely hypothetical construction that would depend almost entirely on the exact details of the specific design in question. There is a large primary mirror, which reflects onto a set of secondary mirrors, which reflect light onto the ring through some sort of transparent membrane. Any or all of those might or might not be coated, shuttered, lensed, ground, etc. in any number of ways.

You want the sky to be blue? Great, the membrane over the ring selectively filters or scatters some red light. You want a day/night cycle? Simple enough, the shutters close on a timer, or the mirrors de-focus at certain times, or the primary's opacity changes, or any number of other things. You want everything to have a constant disco-ball effect? Sure, why not? Break the secondary mirrors up into small segments and spin them in relation to the ring.

Heck, if you want to go really fancy, turn the secondary mirrors into fiber-optic collectors and make the interior of the ring a giant screen made up of trillions of fiber-optic pixels. Then you could even play movies on the sky if you wanted to! Or if you're going for the corporate dystopia vibe instead, advertisements!

I know this is a Doylist answer and not a Watsonian one, but you're writing about a two-kilometer wide orbital ring--an entirely artificial thing requiring significant technological and industrial capabilities. The sky can look however you want it to because that's how you decided it was built. Technobabble and hand-waving can cover a lot in this sort of situation.


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