The Ringworld is an object around 1 million miles wide and with a diameter of approximately 2 AU, encircling a Sun-like star. From what I can tell the surface of the Ringworld is "flat", as in the base of the ring is not curved.

The Sun however has a diameter of roughly 864.938 miles in diameter. Even on our modestly-sized planet of 7.901 miles in diamter around the poles (25 more around the equator) there are rather big differences in the climates in the various regions of Earth: wet, dry, warm, cold and so on.

But when you are talking about an object that has a million... well, "vertical" miles compared to Earth's mere 3950,5 miles, and that the northern and southern parts of Earth are very cold, should the norther and southern parts of the Ringworld's surface (Belts? Wall borders?) not be extremely cold as well?

One of the reasons that the poles are cold because of the slanted angle sunlight goes through the atmosphere because of the Earth's shape. The Ringworld hower is flat, but because of its diameter is so massive (bigger than its star, even!) this effect might be in place as well.

So what I wonder is, is there any description of the Ringworld having such massive ice belts near its rim walls? Is it even possible for them to be there? Or is the inside of the Ring curved, so that all of the Ring's surfaces are the same distance and at the same angle of the sun?

  • Ringworld had 1 million kilometers if I remember right - wasn't wider than its sun so this effect should be very minor. it would need to be at least 10 times wider so it could make a difference, IMO.
    – Mithoron
    Commented Apr 15, 2015 at 10:43

3 Answers 3


Yes. The Spill Mountain people discussed in Ringworld's Children lived on the "Spill Mountains" - as close to the the Ringworld walls you get - or at least as far up as was habitable - and it was described as cold, icy, and snowy. See Chapter 14, The Spill Mountain People.

This probably had more to do with altitude, though.


There doesn't seem to be any difference at the poles. In fact, assuming a perfectly flat ring, the difference in the amount of light from the sun is actually very small, only a few fractions of a percent. The north and south parts should be colder, but not that much.

Okay, for some math. Distances in millions of miles.


So the distance at the north pole is only about 0.01% different than the center of the ring. Bottom line is, it really doesn't make that much of a difference. Similarly, the angle of incidence of the sun at the poles is only slightly different (0.3 degrees). Putting everything together, there should be less than 1% difference in the solar incidence power. Our sun fluctuates by a similar amount.

The reason why Earth's poles are different has little do do with their distance, and more to do with the angle of sunlight hitting them. At the poles, the effective angle of the sun is at the horizon, which means there is just simply far less light on the ground than there is at the equator. Thus, the equator is hotter. If the Earth were a disk, there would be no difference between the poles and the equator in terms of temperature.

I would expect the poles of Ring World to be slightly cooler, as the walls that are at the edge of the Ringworld would in fact be cold. This should lower the temperature slightly of the poles. I don't think in the end this would be a significant effect, but it likely would make some kind of a difference.

  • It isn't the distance, it's the angle, and SJuan's answer did that math. Commented Jan 20, 2015 at 19:01
  • 6
    The polar regions of Earth aren't particularly farther from the sun than the tropics. The variation in distance due to the eccentricity of the Earth's orbit around the Sun is much larger (by a factor of about 750). Commented Jan 20, 2015 at 22:16

In the novel The Ringworld Throne, the lower zones of the mountain wall are described having cold climate, but I doubt they would really be so in reality because:

  • There is no water to form the ice; they are outside the reach of the atmosphere and so there is no water vapour that can condense and freeze

    • At lower altitudes there may be some water vapour in the atmosphere, but also the atmospheric pressure is very low (remember, melting and freezing temperatures get higher when atmospheric pressure gets lower).
  • Most important of all, these wall must be pretty hot. Inclination of the border from the center of the star would be, aprox, arcsin (5E+5/1.5+E8) = 0,19 degrees. Compare that with the aprox 45º inclination caused by the inclination of the axis of Earth.

  • And, being there no atmosphere, there would be no easy way to dissipate that heat (check about why satellites must include radiators to dissipate excess heat).

The only process that could cool the wall region would be air flowing from lower regions, raising up and cooling the middle range (i.e., what happens in the Himalayas). But I doubt that such current would form in the Ringworld, since the wall stops all currents.

  • I'm pretty sure that the OP is asking about on the inside of the wall (where there is a full atmosphere and plenty of water vapor). While your second bullet point is confusing, the information is correct - and you make a good point about the wall itself, though I'm sure the Ringworld engineers would have thought of that and built in a proper cooling system. Commented Jan 20, 2015 at 19:00
  • @Donald.McLean the walls were meant to avoid losing the atmosphera of the ring, so their tops would have been over the limit of the atmosphera (i.e., in space)
    – SJuan76
    Commented Jan 20, 2015 at 19:55
  • Yes, to tops would have been over the limit of the atmosphere, but I'm pretty sure the OP is asking about the "ground" area that is on the inside of the wall, but near it. Commented Jan 20, 2015 at 21:40
  • The wall did emerge far above the atmosphere, but the rim mountains were made of recycled flup (well, mostly the rocky material therefrom). The high altitude parts were cold for the same reason high equatorial mountains on Earth are cold: because of the structure of the atmosphere. Commented Jan 20, 2015 at 23:03
  • If anything they would be colder because they plane of the walls points toward the sun (i.e. the sunlight hits the walls themselves at a very shallow angle indeed). Commented Jan 20, 2015 at 23:04

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