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An infinitely long cylinder, made of planetary matter with an average radius roughly equivalent to the average distance Earth's equator has to its center, orbits around a parallel, infinitely long cylinder made of solar matter with an average radius roughly equivalent to the average radius of Earth's sun, Sol. The 'planet' has an orbit similar to Earth's with regard to distance and shape from the 'sun'. This arrangement is called Cylinder World.

What is a creative way to bestow the 'planet' in Cylinder with seasons? I would especially enjoy a scenario in which different lengths of the planet experience different seasons simultaneously. The 'sun' and 'planet' must remain cylinders and must remain parallel.

EDIT: The 'planet' rotates about its length to produce a day-night cycle similar to Earth's.

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    $\begingroup$ beware infinity! Cylinder word would get burned, because every spot on the cylinder-world would receive solar input not only from a spot in the sky the size of the sun, but from a much larger area... $\endgroup$ – bukwyrm Apr 25 '18 at 8:46
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    $\begingroup$ Put the infinite planet into a noncircular orbit. It wouldn't be eliptical, but such an orbit should exist. $\endgroup$ – Donald Hobson Apr 25 '18 at 10:13
  • $\begingroup$ whatever handwavium they are using to keep these cylinders from collapsing or crashing into each other could just give them seasons. $\endgroup$ – John Apr 25 '18 at 18:25
  • $\begingroup$ @DonaldHobson it would have be extremely elongate to give seasons,but you should write that up as an answer. $\endgroup$ – John Apr 25 '18 at 18:27
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    $\begingroup$ Interestingly, I am pretty sure that due to the shell theorem a truly infinite cylinder wouldn't actually collapse under its own weight. Any given circular cross section would be bounded on both sides by an infinite amount of mass, the gravitational attraction of which would cancel out. Ditto for the mass of the cross section (the shell of the world is...well a shell). Interesting! $\endgroup$ – Draco18s Apr 26 '18 at 2:42
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To avoid too much confusion I am going to state some of my assumptions. I had to edit my answer slightly, to take into account some factors I had realised over the few hours since I posted my original answer. If people don't agree, I can always roll back. I still hold by my answer, although I do think altitude will actually be the biggest factor affecting your temperatures and hence seasons.

When I first pictured the situation, I assumed that your infinitely long planet was infinite along what we would consider the width, or East/West equator, of a normal planet. The North/South radius of the planet being normal dimensions. This results in your planet being infinitely wide with Earth-like cylindrical radius. I use the term latitude to talk about regions North and South from the central equator (which is the horizontal cylindrical latitude that is the receiving the most sunlight). There would be no frozen polar latitudes and you will have to adjust the typical North/South magnetosphere (if your planet even has one).

For a day/night sequence your infinitely long parallel planet has to be rotating on it's infinite East/West axis, with the infinitely long sun on one side. Like a rotissary chicken. This daily rotation is always in the same direction, like a normal planet.

Sunrise and sunset would be on the N/S poles rather than E/W equator of a normal planet (which in your situation is infinitely wide). There would not be any latitude on your planet that had a different amount of sunlight over the day due to an axial tilt, which is responsible for the seasons. Your parallel planet does not have an axial tilt, hence your trouble figuring out the seasons.

To get around this you need to add another component to your parallel planet. You can add a stationary twisted feature along the length of your cylindrical planet. The tightness and height of the twist is up to you, which would affect the concentration and duration of the cooler lee shadows. The twist doesn't bring the planet as a whole any closer to the sun along it's infinite width but rather just twisted regions of it along the cylinder.

Image taken from ScienceDirect

enter image description here

So the 'north' region is twisted closer to the sun while the 'south' is twisted away. This provides different bands of altitudes, and 'shadow areas'. As the planet rotates, each side of the twist would receive the same amount of sunlight through the day. Just always at different times of day. Depending on which way your planet rotated, one side of the twist would always receive more morning sunlight and then be in shadow for the rest of the day.

So you have day/night, various altitudes and temperatures but still equal amounts of sunlight, just at alternating times over the day. So how to get 'seasonal' variation?

To try work around this, you can add an oscillating twist feature along your cylindrical planet. So the 'north' region twists closer to the sun while the 'south' twists away for one cooler 'season'. Then it untwists and equalizes providing a neutral warmer 'season' before twisting in the other direction providing a new different cooler 'season'.

This oscillating twist would take months to work itself through the cycle, providing different seasons where regions receive more morning sunlight and then later in the year more afternoon sunlight, as well as periods with more variation in altitude separated by a periods with a flatter neutral terrain. It would not be as extreme as a typical planet but would be noticeable to some extent. Especially if you had additional rugged topography on top of the 'twist' features, which provided further shadow effects.

These seasons would not be like a typical planets. Those areas within the leeward shadow of the twist will also be cooler than those areas on the sunlight side. Due to the effects of altitude on temperature, higher regions that are much closer to the sun could have a cooler season than those further away from the sun. When these two facts combine, I think your seasons will have a 'banded' nature.

As these twists work themselves in and out, they will result in pockets of isolated regions experiencing different seasonal conditions at the same time of day along the same latitude (as you requested in your question). The height and tightness of the twist affecting the extremes. You can see the 'contours' on the image provided earlier. The more twisted the planet is, the more areas of cooler altitude.

Solar: If you couple this oscillating planetary twist feature with a similar solar twisted feature then you could have more extreme variations in your seasonal conditions. It's more likely that your planetary dynamics of different objects, eg sun and earth, would have the same features working on them with different timescales.

The solar twist would be considerably slower and take 100's to 1000's of years to complete. This slower solar twist could give you changing conditions similar to the aphelion and perihelion cycles. Those lengths of the planet that are furtherest away (aphelion) could be experiencing the equilivant of more extreme winters than I described above and those closer (perihelion) could be having more summerish conditions. Again this would be banded, and leave isolated pockets on your planet experiencing different conditions along the same latitude. Some regions having a milder winters and summers while others are having stonger winters and summers.

**As noted by other answers, you may need to move the planet's orbit a bit further away from the infinite sun. It would be a bright beam of light running across the entire length of the sky and not just an isolated disk.

fyi: This would involve your planet crust and mantle being more 'malleable' than a normal planet consistency. However, you have an infinitely long world orbiting an infinitely long sun while always being parallel to each other. You can work in some malleable planetary physics. :)

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  • $\begingroup$ Since it's infinitely long, any twist towards or away from the sun would put it right through. $\endgroup$ – Cuagau Apr 25 '18 at 8:42
  • $\begingroup$ Twist along the internal axis. Not across. (OP said it was infinitely long cylinder with a similar radius as Earth). So the twisted planet is still parallel to the sun, not twisted into the sun. Hope I understood your comments intention properly. :) $\endgroup$ – EveryBitHelps Apr 25 '18 at 8:46
  • $\begingroup$ Ah. Well, still, a twist on that axis would put both extremes infinitely far away from the sun. $\endgroup$ – Cuagau Apr 25 '18 at 9:10
  • $\begingroup$ @Cuagau, let me know if my edit clarified anything. As far as I am aware, the planet has a normal cylinder radius and is not infinite in that direction. $\endgroup$ – EveryBitHelps Apr 25 '18 at 9:28
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    $\begingroup$ This is neat. Instead of a twist, if you had an oscillation like a standing wave then parts of the cylinder would be closer or farther away. Seasons would propagate down the cylinder with the wave. $\endgroup$ – Willk Apr 25 '18 at 20:54
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The planet's orbit around its sun is strongly elliptical. When it's farther away, it gets cold enough to be winter and when it is near then it is summer.

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  • $\begingroup$ +1 simple yet effective. $\endgroup$ – John Apr 26 '18 at 16:44
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An infinite Cylindrical Moon (CM) would do.

This Moon would behave differently from our own.

  • When it is between Cylindrical Earth (CE) and Cylindrical Sun (CS), it is winter, for this is when the least amount of light will reach CE.
  • As CM moves away to unblock sunlight from CE, spring starts. CE gets increasingly more light.
  • At some point, CM starts reflecting light towards CE, which then gets a summer. The summer peaks when CM is full.
  • As CM wanes, autumn/fall begins. This autumn, however, is more like a milder summer.
  • When CM starts coming out of CE's shadow (thus waxing for the second time in its cycle), temperatures rise. This is the second summer in the cycle.
  • When CM stops reflecting light towards CE, a second spring happens. Compared to the first one, this one is in reverse.
  • CM finally starts blocking sunlight again, closing the cycle with another winter.

Notice that CM does not have to be constrained by the same lunation period and apparent size in the sky as our own round Moon. It may have a longer lunation, and a smaller apparent size... This way, it will never cause an eclipse, thus there is no eternal night during the New Moon phase.

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  • $\begingroup$ In this case you will have eternal night during the dead of winter (full eclipse) and typical half day and half night in the middle of summer. $\endgroup$ – EveryBitHelps Apr 25 '18 at 17:47
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    $\begingroup$ @EveryBitHelps it depends on how long a lunation takes, and the apparent size of the moon in the sky. They don't have to be the same as ours. $\endgroup$ – Renan Apr 25 '18 at 17:53
  • $\begingroup$ True. Wouldn't in this scenario a single lunation be a "year"? So however many days/months it takes to cycle through the moon cycle and associated seasons would count as one year. From midsummer to midsummer or something. $\endgroup$ – EveryBitHelps Apr 25 '18 at 18:22
  • $\begingroup$ @EveryBitHelps Indeed. In such a setup, lunar years might be the global standard for timekeeping. $\endgroup$ – Renan Apr 25 '18 at 18:52
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    $\begingroup$ Very cool! I like your solution to the eclipse problem by having the moon be too small or too far away to allow for an eclipse. I also like how this adds another infinite cylinder. The more the better! $\endgroup$ – TheNewGuy Apr 26 '18 at 5:41
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EDIT: Okay, how about this...

enter image description here

Original answer below...

enter image description here

...Basically the cylinder that is the sun goes wider than the cylinder that is the planet. Both still cylinders.

As for day night cycles Larry Niven solved that problem in Ringworld. I don't like his solution, but it works. Check it out.

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  • $\begingroup$ That is alot of sun! $\endgroup$ – EveryBitHelps Apr 25 '18 at 17:34
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    $\begingroup$ A torus is one interpretation of an 'infinite' cylinder. This both makes the problem more tractable, and provides an effective solution to the original question. $\endgroup$ – kingledion Apr 25 '18 at 17:39
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    $\begingroup$ Having looked at the diagram for abit, the planet couldn't rotate for a day/night sequence. At least not in the normal sense. So one side of the planet will always be closer to the sun than the other, and be fully day throughout the planet's existence. The internal side of the planet will have a varying shades of eternal dusk situation with the central portion (equatorial line) having permanent darkness as the other side of the parallel torus planet creates an eclipse with the other sides of the sun. Shew! I think I described that correctly. $\endgroup$ – EveryBitHelps Apr 25 '18 at 17:59
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    $\begingroup$ inter linked rings might work better, like links on a chain. especially if offset slightly. Of course neither will allow for a day/night cycle. Still love the torus idea. $\endgroup$ – John Apr 25 '18 at 18:29
  • $\begingroup$ It's a clever solution for inducing seasons, but unfortunately I am not going for tori. $\endgroup$ – TheNewGuy Apr 26 '18 at 5:28
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Perhaps the solar cylinder has variable brightness, with hot and cold areas evenly separated and moving along its length at a constant speed. Parts of the planetary cylinder that are currently near a hot patch will experience summer, while other parts near a cold patch will experience winter.

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Lets say north and south are along the length of the cylinder, and east and west are around it. Standing on the planet, looking east and west would look just like earth, with the horizon dropping off a few miles out at sea level. Looking to the north or south, though, you would see triangles angling out to a single point. From above, the infinite line of the sun would stretch out out to that same point. Looking east at dawn, you would see the line of the sun suddenly emerge from the entire horizon at once, before proceeding on it's daily arc overhead.

On Earth, the sun takes up about 0.5 degrees horizontally. This sun would take up 180 degrees. If it puts out similar energy per surface area, this means it would have to be about 300 times smaller vertically to avoid roasting the planet, or about 6 arcseconds. This is incredibly small--it would be the same size as a 6cm diameter cable viewed from a distance of 2kms. Still, it is about 8 times larger than the largest stars, so with how bright it is, it would still be quite visible (but not so tough to stare at, since you could only see a portion of it at a time).

On this world, gravity would have to not act in one of the 3 dimensions (along the length of the cylinders), or you would be spaghettified by the infinite mass at either end of you. The distance between the sun and planet would always be the same along the entire length (definition of parallel), so if the sun was uniform, then although there would be a night/day cycle, then all parts of the world would go through the same seasons at the same time, as the cylinder moves in an eliptical orbit closer and further from the sun at all points at once. And all parts of the world would have an identical climate.

The only way to have different seasons is if the sun grows hotter and colder at different points along its length. Places below the cold spot would shift to winter, then back to summer when it warms up. Or the hot and cold spots could be fixed, and the sun could be moving lengthwise relative to the planet. In this case, if you heard word that the people north of you just had a long hard winter, you know that you're getting that long cold spot next.

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