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East poles and west poles and tidelocked planets

 
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eldin raigmore
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PostPosted: Sat Oct 12, 2013 7:49 pm    Post subject: East poles and west poles and tidelocked planets Reply with quote

Given a direction, a pole for that direction is a place from which one can travel no further in that direction; and/or, a place which is that direction from any other place.

For example, the North Pole is north of everywhere else; from the North Pole it is impossible to travel in any northerly direction, only southerly.
And, the South Pole is south of everywhere else; from the South Pole it is impossible to travel in any southerly direction, only northerly.

A planet which rotates with respect to its primary star (its "sun"), that is, it rotates more often than it revolves around its "sun", can't have an East Pole or a West Pole. East is the direction in which the sun last rose and will next rise; one can keep going east for as long as the planet and its relationship to its sun last, one will merely be traveling in a circle. Similarly, West is the direction in which the sun last set and will next set, and one can travel west indefinitely, but one will be circling the planet by doing so.

However, what if the planet always keeps the same face towards its sun?

Then it might have six relevant poles; a Noon Pole, a Midnight Pole, a Dawn Pole or East Pole, a Sunset Pole or West Pole, a North Pole, and a South Pole.

The Noon Pole would be the spot on the planet above which the sun always appears to be directly overhead all year long.
The Midninght Pole would be antipodal to the Noon Pole. If one were to stand on the Midnight Pole one's feet would be pointing towards the sun, through the center of the planet.

The Dawn Pole or Sunrise Pole or East Pole would be on the terminator between daylight and nightdark. It would be one of the places that terminator intersects the "equator", (though "equator" is perhaps a bit of a misnomer for anything on a tidelocked planet without equinoxes or solstices or seasons). It would be the leading point of the planet in its revolution along its orbit about its sun.

The Dusk Pole or Sunset Pole or West Pole would also be on the terminator between daylight and nightdark. It would be the other place that terminator intersects the "equator". It would be the trailing point of the planet in its revolution along its orbit about its sun. It would be antipodal to the East Pole.

The "equator" would go through the East Pole, the Noon Pole, the West Pole, and the Midnight Pole.

The North Pole and the South Pole would be less important than the other four poles. And/or, defining them would require referring to some of the other four poles. If one stands on the Noon Pole and faces the East Pole, then South will be to one's right and North will be to one's left. The point on the terminator directly to one's right will be the South Pole, and the point on the terminator directly to one's left will be the North Pole.

The terminator would be the great circle running through the East Pole, the South Pole, the West Pole, and the North Pole.

I don't know of any non-cultural reason to pick any particular name for the great circle running through the Noon, South, Midnight, and North Poles; but it would probably be considered the Prime Meridian, unless the Terminator is so considered.

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Actually, a "moon" -- a satellite tidelocked to its planet -- might also have the same six poles.

The Noon and Midnight poles would need to be renamed, because it would be the planet, rather than the sun, that always appears directly overhead of the "Noon" pole. I suppose one could name them the Near Pole and the Far Pole; the Near Pole would be the point on the satellite closest to the planet, and the Far Pole would be the point on the satellite farthest from its primary planet.

The satellite would have dawns and dusks; its terminator would move relative to its surface (or vice-versa, depending how you look at it, its surface would spin out from under its terminator and back in). Nevertheless, since the satellite's orbital plane about its primary planet is likely to be just a few degrees away from the planet's own equatorial plane, and the satellite's orbital motion is likely to be in almost the same direction as the planet's rotational motion, one could take the terms East and West to refer to the planet's East and West, rather than the satellite's.

The satellite's East Pole, then, would be the point on the satellite furthest planet's-East; it would (probably) be the leading point of the satellite in its orbit about its primary planet. And the satellite's West Pole would be the point on the satellite furthest planet's-West; it would (probably) be the trailing point of the satellite in its orbit about its primary planet.



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Any comments? Any reaction?
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Aert



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PostPosted: Fri Oct 18, 2013 7:41 pm    Post subject: Reply with quote

Well explained!

Just wondering, can planets be tide-locked as well as moons? I know Venus rotates very slowly but it still rotates.

I also wonder what kind of life, if any, could evolve on such a planet - or if the temperature differential would limit or prohibit the expansion of life.

Moons aren't as problematic, obviously, but the referential directionality you mentioned is interesting - I suppose it has to depend on if you're on the planet or the moon.
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LingoDingo
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PostPosted: Sat Oct 19, 2013 5:41 pm    Post subject: Reply with quote

Such a planet, if too stable, would be unable to generate complex life forms, or even sustain any alien life attempting refuge on it. Even terraforming would be ineffective.

However, most tidelocked planets aren't perfectly stable. If you were to watch a timelapse of our moon over it's 28 day cycle you would see a slight shift to the west and then east.

In terms of what this would mean for evolution. The zone created on the "terminator", as eldin called it, would be as capable of producing complex life forms as the Earth is.

This would obviously then make that area of immense cultural significance to any intelligent species that might evolve there.

I would imagine that any ideologies cropping up would likely be fairly similar to the Nordic creation story.
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eldin raigmore
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PostPosted: Sun Oct 20, 2013 8:17 pm    Post subject: Reply with quote

Even if the entire planet could support life, the terminator would be an ecotone, like a forest-edge or an estuary.

It would contain not only dayside-species and nightside-species, but also some species that occur only in the terminator.

In real life humans are a forest-edge species. If there are too many trees we cut some down; if there are too few trees we plant some.

If a tide-locked planet supports intelligent life, it seems reasonable that it would first arise in and around the terminator (the "Twilight Zone").

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Aert wrote:
Just wondering, can planets be tide-locked as well as moons?

Yes, they can.
Either Venus or Mercury is or was once thought to be tide-locked, with its "day" equal to its "year". But now one of them (I don't know which one) is thought to have a "year" that's one-and-a-half "days" long; in other words a "day" is two-thirds of a "year".
But anyway, yes, a planet can get tide-locked to its primary star.
I'm not sure what the pre-requisites are. I had the idea that the planet would have to be closer to the star than Earth is to Sol. I'm not sure that's true.


Aert wrote:
I also wonder what kind of life, if any, could evolve on such a planet - or if the temperature differential would limit or prohibit the expansion of life.

Some don't think life could get a foothold on such a planet; especially not "native" life, life that originated there.
I'm not sure. If that's true I'd like to see calculations and/or references.
Absent such proof, I'd rather believe that life could arise there, and pretend that a narrow band of life-sustaining land near the terminator on the nightside, and a broader band of life-sustaining land near the terminator on the dayside, had life.
I would expect that the intelligent autochthons wouldn't actually colonize the Noon Pole or the nightside until they'd attained technological civilization.

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LingoDingo wrote:
Such a planet, if too stable, would be unable to generate complex life forms, or even sustain any alien life attempting refuge on it. Even terraforming would be ineffective.

I'd rather think it was merely difficult and imperfect, than impossible.


LingoDingo wrote:
However, most tidelocked planets aren't perfectly stable.

Every planet and satellite in our solar system "nutates" ("nods"); its axis rocks rhythmically around a line perpendicular to its axis (not necessarily parallel to its orbital plane).
Those that rotate also precess; the axis slowly rotates around a line perpendicular to the orbital plane. Earth's axis, for instance, now points at Polaris. Some time ago it pointed at Vega. But before that it was pointed at Polaris. In the future it will point at Vega again; and some time after that, at Polaris again. It precesses around once every 26,000 years.
A tide-locked body's orbital path is elliptical, not circular. At each point in its orbit it shows approximately the same face to its primary as it did the last time it was at that point. But it doesn't have to show exactly the same face at every point in the orbit as at every other point; points on its surface trace out circles as it rotates, but the orbit is elliptical.


LingoDingo wrote:
In terms of what this would mean for evolution. The zone created on the "terminator", as eldin called it, would be as capable of producing complex life forms as the Earth is.
This would obviously then make that area of immense cultural significance to any intelligent species that might evolve there.

Yeah! Smile
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PostPosted: Sun Oct 20, 2013 8:48 pm    Post subject: Reply with quote

I don't believe that any part of the planet other than the terminator zone could support the development of complex organisms. After all, the primary driving factor of evolutionary change is geological and climate instability. It's only when the environment puts pressure on organisms that their evolution accelerates.

There are countless instances in the real world of organisms finding a consistent niche and remaining more or less unchanged for millions and even tens of millions of years, e.g. many marine creatures or ferns.

The areas of our tidelocked planet outside of the terminator would be incredibly stable environmentally, one side extremely hot and the other extremely cold. Even if the planet were positioned such that one side woud have a temperature cable of sustaining liquid water, the lack of pressure put on any budding microorganisms would prevent them from evolving any further.

As such, I can only expect to find complex growth occuring in the terminator. It would also be immensely helpful if the terminator could shift at least a few dozen kilometers or more throughout the orbit. The shift from day to night over the course of the year would hopefully force the organisms to become more complex in order to deal with the temperature changes associated with that cycle.

In any case, the two non-terminator faces of the planet would have climates too extreme and too stable to permit anything beyond single-celled organisms form living there.

This, however, does present an interesting barrier for the development of any intelligent species. The advancement of technology would require more and more resources, and it's highly unlikely that the terminator zone would be able to support that forever. Which would mean that, at some point along the line, the species, which I'll just go ahead and call terminators, will have to make attempts to acquire resources from the two extreme faces. The question being, how different stages of technological development might try to deal with that.
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eldin raigmore
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PostPosted: Mon Oct 21, 2013 10:12 pm    Post subject: Reply with quote

I think "competition" would be a driver even in a geologically and climatologically and chemically very stable environment.

While I wouldn't expect life to originate too far way from the terminator, I'd expect it would gradually evolve to go further and further towards the poles, perhaps even to places where water was frequently gaseous or solid. These organisms might not be "complex" in the sense of being multi-cellular; or they might. (Perhaps they would still be microbes even when multi-cellular; or, IMO, perhaps not.) Extremophiles, and organisms that can estivate and/or hibernate (or processes equivalent to those), such as tardigrades, might very well survive near the poles, or at least far from the terminator; the advantage would be that that way they could escape the competition from other organisms that have to stay closer to the terminator.

I would expect life to get further from the terminator on the dayside than on the nightside. The problem is, where does their energy come from? On Earth, there are many organisms that live in caves etc. where the Sun never shines. ("Many" in the sense that I couldn't count them; I believe all such communities are in fact rather sparsely populated.) Some of them are macroscopic, such as eyeless fish and eyeless spiders. I don't know how their ecosystem gets the energy to keep it going, but somehow it does. (The ocean-bottom ecological communities get their energy by either feeding on what falls from higher up, or from geological sources like thermal vents. So although the sunshine there is so attenuated one might as well say it never shines there, nevertheless we know where its energy comes from.)

Living organisms don't need to live very fast or very intensely; and when sometimes they do live fast, they don't have to live fast all the time.


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*Here* in Our Time Line on Real-Life Earth-Prime, humans even before modern technology managed to settle or otherwise inhabit all sorts of places and environments that weren't at all like the savannah-forest or savannah-beach or forest-beach edges humans evolved to inhabit. Before "civilization" we spread to almost every bit of land except Antarctica and the tiniest islands. Before "modern" times we had spread to the North Pole and to the deserts; (actually I think we made it to the North Pole and to the deserts prehistorically, though if I am wrong it wouldn't hurt my point that I'm trying to make).

With the beginning of industrial "modern" technology we started to have people living on Antarctica for part of their lives, though AFAIK nobody has ever been born there, much less raised there, and nobody has ever intended to stay there long enough to "die of old age" and be buried there. I don't know if anyone has ever been married there or been to school there.

We've also had people for extended stays below the surface of the ocean.

And there are houseboat communities a bit like villages or towns (or cities?) where most folks almost never have dry land under their feet, though TTBOMK all of these communities are near land. (Individual boats may go far out to sea, but they always intend to return to the communities near land, AIUI.)


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So, yeah, I think the "conquest" of the interiors of the dayside and the nightside would be major accomplishments, like climbing Everest or going to the poles or crossing Africa both north-to-south and east-to-west, or going on the Hajj. Not everyone could do it -- most people couldn't do it at all, or most people couldn't do it more than once (like climbing Fuji rather than like climbing Everest). But a civilization would feel it was something to celebrate once one of their members ("citizens"?) managed it.
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