I'm working on a sci-fi/fantasy story that involves a future earth that has become tidal locked with the sun. Part of the story has an advanced civilization that has built a ring (halo) that circles the planet and provided an artificial night cycle for the sun facing part of the planet. As far-fetched as it is, how habitable would the planet be if a night cycle were reintroduced artificially? I know strong storms would form based on the flow of extreme cold air/hot air, but would it be fairly similar to our current climate?


  • $\begingroup$ Does the ring completely cover the "day" side during the night? $\endgroup$
    – Zxyrra
    Commented Feb 12, 2017 at 2:22
  • $\begingroup$ Not completely. I was thinking that it could travel at a quicker speed then the current rotation of the planet, which might offset the reduced size of the night cycle? It would cause the days to be shorter overall. $\endgroup$
    – jnhaswell
    Commented Feb 12, 2017 at 2:29
  • $\begingroup$ That's an awesome first question. $\endgroup$
    – PatJ
    Commented Feb 12, 2017 at 2:30

2 Answers 2



Forgive me if I make a few assumptions, but it seems that this ring is rather large, considering that its able to completely block sunlight from hitting the earth. I'm also gonna assume that there are gaps or open areas in the ring as its way of switching between night and day on the light side of the planet.

Luckily for the people on that alternate Earth, people have already worked out if something like this is possible, with a few difference. As a matter of fact, its been something thought about doing to a planet in this solar system. It's the sweet young lady next door named Venus!

While instead of using a ring, its been theorized that a giant sunshade would be placed between Venus and the sun, blocking the light and cooling it down. The sunshade could then orbit Venus, allowing the light side face to experience day and night. This ring world of yours could do the exact same thing, although the cost to build it would be a bit larger.

However, why stop on just the side facing the sun? Those poor chaps living on the back side of this Earth want a little sunlight too! So how about we toss some big reflectors extending from the top and bottom of the inner part of the ring so that when the light can be bounced to dark side of the planet, which can be used to give both sides of the planet a day and night cycle.

Or if that doesn't work, then while a ringworld without any gaps in it blocks out the sunlight, a large reflector could be placed in a polar orbit and could provide the Earth with sunlight. Although, neat enough, this would cause the planet's light source to rise and set in the north and south instead of east and west.

If it's all done right, it should be possible to limit any major effects on the weather. I would assume, at least.

Here is a link to the paper detailing plans to terraform Venus, which includes the idea of sunshades, reflectors, and more.


Hope I helped!

  • $\begingroup$ Very helpful! I believe the ring wouldn't quite be as large as half the planet, but my thoughts were a speed up of the ring to offset this. It would shorten the day and cause more in a given year, but my hope is this would regulate the temperature. Although I agree completely that reflectors would make a lot of sense - for the stories purposes I'm trying to keep the dark side as is. My main concern was making sure a normal civilization could be sustained with this fictional plot device. Thanks again!!! $\endgroup$
    – jnhaswell
    Commented Feb 12, 2017 at 2:56
  • $\begingroup$ Glad I could help! Since you're trying to keep the dark side as it is, then it may still be able to support moderate temperatures at least on coastal areas. Like how ocean currents now take water from the equator and disperse it to areas that would normally be much colder, in this case the currents would carry heat from the light side to the dark side. Depending on what kind of greenhouse effect the planet has going on, it's also opens up the the ability for some inland areas to remain relatively habitable.Aside from the no sunlight of course. $\endgroup$
    – rclev
    Commented Feb 12, 2017 at 3:04
  • $\begingroup$ And I would expect some very strong storms, but I'm not sure on that. $\endgroup$
    – rclev
    Commented Feb 12, 2017 at 3:07

As I understand it the timescale for the Earth to tidally lock to the Sun is of the order of some 40 billion years (probably longer).

And to put that in perspective, in something like a mere 5 billion years the Sun will expand into a red giant.

Worrying about day and night is going to be the least significant issue someone on Earth faces at that point. And on technology timescales like that, it is hard to conceive of the even a small minority of the then human population living on Earth.


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