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Almost all illustrations of ringworlds that I've come across tend to show off the shape of the ringworld from the surface.

This doesn't seem realistic to me, because the ringworld's radius would probably be so big that the curvature wouldn't be noticeable, especially in the presence of an atmosphere (due to light scattering).

One explanation for these portrayals that I can imagine is that maybe an illustrator has no way to represent the ring shape and the fact that it's a habitable world without resorting to some unrealistic visuals.

Am I wrong in thinking that the great radius and the light scattering would prevent inhabitants from seeing the ringworld's shape, or is this indeed just artistic license for practical purposes?

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  • $\begingroup$ Are they all ringworlds or are some orbitals? Orbitals are much smaller so the curvature would be more visible. $\endgroup$
    – Tim B
    Commented Dec 7, 2018 at 9:41
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    $\begingroup$ Have u ever notice that when u look up into the night sky and see a ufo or moon which is very very bright, the moon is much much farther than the diameter of ur ringworld and you should be able to see the entire structure during day too unless of course today is scheduled for heavy downfall. $\endgroup$
    – user6760
    Commented Dec 7, 2018 at 9:50
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    $\begingroup$ @Kleronomas citation? $\endgroup$
    – RonJohn
    Commented Dec 7, 2018 at 11:03
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    $\begingroup$ @Kleronomas 5 times the earth moon distance puts the ring at 1.5 million kilometers above the star's surface and well into the star's corona which is 1 million Kelvin plasma. I don't think carbon based life forms can survive that. At least it is well outside the habitable zone. $\endgroup$
    – GretchenV
    Commented Dec 7, 2018 at 12:12
  • $\begingroup$ @GretchenV Ah, you're right. I did a search from my phone and I carelessly read the wrong number. Still, my point is that the moon isn't farther away from the Earth than the diameter of my ringworld (as suggested in another comment), but the other way around. $\endgroup$
    – Sigma Ori
    Commented Dec 7, 2018 at 12:55

3 Answers 3

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Is it really possible to see across a ringworld?

Yes, it is.

Remember that the world is shaped like a ring, and due to the rotation used to simulate gravity, the atmosphere will mostly be located close to the ring, leaving the center space-level empty.

With that in mind, when you look on the other side of the ring the visual rays reaching your eyes actually travel through a thinner layer of air than those coming from an adjacent region.

Look at the schematic below (not in scale):

ring world atmosphere

When you look at an object along line of sight B you are actually looking through a larger layer of air than when you are looking along the line of sight C.

This means that you will see the image of the ring world fading away where the optical path goes through more air and then becoming sharper.

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    $\begingroup$ I think you misunderstood the question maybe? Obviously light from the ringworld far away can reach you but I suspect the apparent size would be much much smaller than the one shown in the pictures $\endgroup$
    – SilverCookies
    Commented Dec 7, 2018 at 14:06
  • $\begingroup$ Very interesting that with the proper tools, you can see distant regions more clearly than relatively nearby ones. $\endgroup$
    – Nuclear Hoagie
    Commented Dec 7, 2018 at 14:15
  • $\begingroup$ @SilverCookies, OP is not asking about apparent size $\endgroup$
    – L.Dutch ♦
    Commented Dec 7, 2018 at 14:26
  • $\begingroup$ @L.Dutch I interpreted the question as if it meant if it was possible to see the ringworld curving upward using only one's sight, not with instuments $\endgroup$
    – SilverCookies
    Commented Dec 7, 2018 at 14:56
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    $\begingroup$ @SilverCookies, but since OP is not setting the width of the ring, it cannot be excluded that is visible as a whole with the naked eye $\endgroup$
    – L.Dutch ♦
    Commented Dec 7, 2018 at 15:02
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For the purpose of illustration let's assume the Ringworld has a radius of 1AU and is as broad as earth is wide, so around 12000km. There are two differen aspects to your question: How does the curvature of the Ring look like from it's surface and how bright is it.

Assuming an Earth-like surface we can assume around the same absolute magnitude for a roughly earth-sized segment as for earth. Given that we can see Venus just fine and it is one of the brightest objects in the night sky the ring, which is much bigger should be quite obvious in the night sky (I'm assuming a Niven-style day/night system here where an inner ring with partial segments rotates to block the sun for night time over a part of the Ringworld). You would see a segmented line go right over your head. I don't expect you to see anything during the day though since you can't see Venus either when the sun is up an noon, and on a Ringworld it's always noon or solar eclipse night.

As for the curvature near the horizon that's more tricky. With geometry (Thales' theorem is useful here) it's clear that distance of two points on a circle is Diameter times sin(x) where x is the angle between the circle tangent at one point and the secant connecting the two points. So if you're looking at a part of the ringworld the angle x is what you have to look up from your local horizontal.

You can see stars even just a couple of degrees over the horizon so we can go deep. At 2° you are looking 35 light seconds away. Earth in that distance would have an angular diameter of about four arc minutes. That's not big, about one sixth of the full moon. So you could see that it has a diameter and probably even some structure if you have good eyes or a primitive telescope. But it's not the big "circle curves in to become your horizon" a lot of ring world illustrations show.

Tl,dr: In the dark it should be a bright line going over the sky. But the curvature and nature as a circle only becomes visible at low angles so you could easily imagine people living in regions with hills and low visibility and you could miss the circle nature of the world from there. At an ocean with good conditions it should be obvious though.

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  • $\begingroup$ It looks deceptively flat, and two ribbons stick-out on opposite sides of the horizon. I think this picture is convincing, but the widening at the base may be tapering more quickly.news.povray.org/povray.binaries.images/thread/… $\endgroup$
    – Christmas Snow
    Commented Dec 7, 2018 at 18:59
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    $\begingroup$ The Ringworld (capital R) is 1 million miles across. Much more visible than Venus. $\endgroup$
    – Loren Pechtel
    Commented Dec 8, 2018 at 2:01
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You’d most certainly be able to see the ringworlds shape, and you’d be able to tell that you’re living on one. You can see the moon from earth despite the atmosphere.

Maybe the immediate horizon (few hundred miles) might be impossible to see. Im sure someone could science it up and give you a solid answer on distance. However, you would be able to see the ring rise up into the sky (eventually)

You’re basically standing on top of a mountain because the ring is curving upwards. No matter where you stand everything is curving away from you. On Earth it curves out of your field of view, but on this ring it curves upwards into your field of view.

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