Leiyan

The Moons of Roshar

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This is awesome. Just one piece of info to add to your brilliant coalition of information: I'm pretty sure that Peter said that they do not have perfect orbits (can't remember exact terminology, but sometimes they are really close to Roshar, and other times really far. An eliptical orbit, I think). But anyways, this is cool. I think I'm going to ask Brandon about this at the signing.

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There are some flaws in this analysis that should become apparent.

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This is awesome. Just one piece of info to add to your brilliant coalition of information: I'm pretty sure that Peter said that they do not have perfect orbits (can't remember exact terminology, but sometimes they are really close to Roshar, and other times really far. An eliptical orbit, I think). But anyways, this is cool. I think I'm going to ask Brandon about this at the signing.

I covered elliptical orbits, but I didn't out right say that. Eccentricity is a measure of how elliptical an orbit is. I pointed out that even Mars, with its highly eccentric orbit has asteroids at its Lagrange an points. However, I'm not brushed up enough on orbits and eccentricity to test how elliptical an orbit can get...more thoughts for later.

Please let me know what you ask and what response you get!! I'm also attending a signing and have some questions in mind, would hate to repeat you!

There are some flaws in this analysis that should become apparent.

Well, it's my first shot at this sort of thing. =) I hope you mean the flaws will become apparent in WoR? Edited by Leiyan
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Heh, I know nothing, other than the speculation I've seen in the other threads that touch on this. 

 

 

Roshar's moons are much much closer than our moon. Their elliptical orbits bring them closer to Roshar's surface during the night than geosynchronous altitude.

-Peter

 

This should impact things significantly, I think. It was in a fairly recent thread. Great job, Leiyan, he who knows more about moons than I do. :D

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Oh I didn't catch that one! Hmm! OK I also admit I did read a post saying they were closer than synchronous atltitude, like Phobos, and I kinda skipped past factoring that for now...but I didn't catch just how eccentric the orbits were described by Peter. I can't wait to try and figure all this out. =D.

Edit: But in the morning when I can think better. >.>

Edited by Leiyan
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I agree with the Lagrangian points and Nomon being the second body.

 

About the orbit size: it can be calculated from Roshar's mass and moons' orbiting time.

 

Yes, I believe the moons always rise and set at the same hour. Also they rise at east and set at west, like the sun. Which means they are synchronised with the sun's position on the sky. This sets their orbiting time to the same as Roshar's orbiting of the sun. (Indeed, and not to one day! I'll post some gifs to explain, but I'm kinda busy.) Which is rather long, but actually unknown (as I've mentioned in another thread, I don't see why time between Weepings would have to be the time it takes the planet to orbit the sun). This implies a big orbit radius.

 

If the moons are on sky at daytime, just invisible, they could have much shorter period and therefore orbit radius.

 

PS: Can anyone give source link about the high eccentricity?

Edited by Eri
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I though peter mentioned that they come closer than geosynchronous orbit?

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Any link? Edit: Thank you.

 

Also, I'm not suggesting geostationery orbit; tis wouldn't actually make sense.

 

Though if they come closer than geostationary… wow, this must be a really spiky ellipse. If they are "much closer" in general and really are on the sky one time per day, and go from east to west then I must be missing something, because I don't see how it would make sense.

 

But I suppose they do get much further and the long axis is what I thought the radius will be.

 

BTW does anyone know how hich eccentricity (of moon's orbit, not planet's) affect Lagrangian points? I couldn't find in on Google.

Edited by Eri
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yeah, we know the orbital period is one rosharan day (20 hours for us), and roshar gravity is 0.7 g, so we should be able to calculate geosyncronous orbit. I'm too lazy, and too rusty on that, to do it myself. I also don't know how eccentricity fits into it

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yeah, we know the orbital period is one rosharan day (20 hours for us),

This is not true.

Take the planet's rotation into account. I really don't have time to do the gifs, but a period of 1 day = something "hangs" in the same point of the sky (think: Calamity in Steelheart), not it appears always at the same hour.

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Leiyan, upvote for all the research.  Very informative.

 

However, It is not at all clear that all three moons share the same orbital plane.

 

Can anyone shed light on whether Lagrange points can exist in a highly elliptical orbit with three orbiting bodies in the same orbital, i.e. one in which the distance of the orbiting mass to focus constantly varies, and would vary significantly at each moment amongst the three moons (which may or may not have differing masses)? 

 

Each moon moving across the sky in only a few hours implies a high orbiting velocity for the time in which they are visible in the night sky, or a quick rotational velocity of Roshar, or both.  I don't know how a Rosharian day compares to an earth day, nor do I know Roshar's diameter; but high orbiting velocity seems to fit well with a highly eccentric orbit with Roshar at one focus, as the moon slingshots past Roshar.

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Take the planet's rotation into account. I really don't have time to do the gifs, but a period of 1 day = something "hangs" in the same point of the sky (think: Calamity in Steelheart), not it appears always at the same hour.

 

Do we know for a fact that the direction of Roshar's rotation is the same direction of orbit for the moons?  I was under the impression that they are in different directions, one clockwise, the other counterclockwise.

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An elliptical orbit bringing a Phobos sized moon out of geosynchronous orbit would appear larger than the .14° Leiyan is proposing wouldn't it? 

 

His Szeth quote also mentions that Nomon only gives a little more light than Salas, not necessarily alot more light.

Being that Salas produces violet light I think it's fair to say that it does a poor job of actually illuminating nighttime Roshar. Yet Kaladin and Rock are able to see well enough by it to make their way through camp by it.

But if Nomon, a blue white moon, only produces slightly more light, then it probably isn't much larger (to appearances) than Salas.

 

All this is to say that I don't think they're necessarily in the same orbit around Roshar. Since we are aware that they appear in the same order every night for thousands of years, I think its more than nature taking it's course. That seems artificial.

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@Leiyan, you said "I don’t recall any mention of Salas and Nomon being in the sky together, but if my Lagrangian point theory holds I would keep an eye out for it in the upcoming books."

However, you missed one quote about the moons in Szeth's interlude "a work off art"

"It was the time between the first two moons, the darkest period of the night. The hateful hour, his people called it..."

Otherwise, I like your analysis, it makes sense to a non-astronomer.

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@Leiyan, you said "I don’t recall any mention of Salas and Nomon being in the sky together, but if my Lagrangian point theory holds I would keep an eye out for it in the upcoming books."

However, you missed one quote about the moons in Szeth's interlude "a work off art"

"It was the time between the first two moons, the darkest period of the night. The hateful hour, his people called it..."

Otherwise, I like your analysis, it makes sense to a non-astronomer.

 

Oh, great catch, thank you!  I'm putting all these quotes into an excel spreadsheet... hopefully, I'll get time to turn this into a database...  I have some more ideas I am currently working out. =D

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Okay, I still believe these moons must share the same orbit, in order to always appear in the same order, and at the same time night to night.  They wouldn't call them "First" "Second" and "Third" Sister if they weren't always in order, and, as Mysty pointed out, they wouldn't have a name for the time between Salas and Nomon ("It was the time between the first two moons, the darkest period of the night. The hateful hour, his people called it...", I-6) if it wasn't consistent.  Though, I still need to math out how/where the moons could exist in a shared orbit before I can back this up fully.

 

 


 
Roshar's moons are much much closer than our moon. Their elliptical orbits bring them closer to Roshar's surface during the night than geosynchronous altitude.

-Peter

 

I totally missed this before....the elliptical orbits bring them closer to Roshar's surface during the night... always during the night.

 

So the elliptical orbit of the moons must precess such that the apogee (furthest point from Roshar) is always pointing towards the sun, and the perigee (closest point to Roshar) is always pointing away from the sun.

 

Here's a badly drawn image to illustrate...  It's the (out of scale) location of Roshar, and the orbit of Roshar's moons, as Roshar orbits relative to the sun.

 

post-8393-0-68922100-1393699772_thumb.jp

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 I don't know how a Rosharian day compares to an earth day, nor do I know Roshar's diameter; but high orbiting velocity seems to fit well with a highly eccentric orbit with Roshar at one focus, as the moon slingshots past Roshar.

Roshar day = 1/500 R year = 1.1 Earth year / 500 = about 0.78 Earth day = a little below 19 Earth hours

Do we know for a fact that the direction of Roshar's rotation is the same direction of orbit for the moons?  I was under the impression that they are in different directions, one clockwise, the other counterclockwise.

Erm... I'm not sure if I understand your question, but we know that moons' and sun's perceived movement is in the same direction (they rise at east and set at west). At least sun and 2 of the moons I'm sure of.

Direction of moons' orbit is a hard one... according to my hypothesis (synced with Roshar orbiting its star) we can't know it, because it depends on Roshar's orbiting, not its rotation. I think.

However I'm not really good at astronomy, most of my "research" about Roshar astronomy = I've asked my husband (who studied physics) and I've read Wikipedia.

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I love reading analysis from someone who clearly has a science background. It takes something I just passed over without a thought in the text and makes it much more interesting.

 

All of this suggests to me that the moons are actually artificial. Roshar has a very... strange... relationship with technology that is hard to relate to, but it seems quite within the realm of possibility that the moons were made and placed into orbit, maybe for observation, maybe as bases. 

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Do we know for a fact that the direction of Roshar's rotation is the same direction of orbit for the moons?  I was under the impression that they are in different directions, one clockwise, the other counterclockwise.

 

I believe you are correct.

 

Roshar spins CCW and the lunar orbit travels CW (or vice versa).  If Salas rises in the sky opposite the sunset as seen from Alethkar, and then remains in the sky during the night, it cannot be moving the same direction as Roshars rotation at high orbital speed, or it would just disappear below the eastern horizon and stay ahead of the visible nighttime sky as seen from Alethkar.

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I have more ideas I want to share about the moons, basically a complete revision of my opening post… please keep in mind, this is all preliminary, based on limited observations, and I expect revisions and we get more info…

 

First, since it is already known that Roshar does not have an axes title (http://lunarubato.tumblr.com/post/42954839930/ok-so-here-is-the-information-we-collected-from), we know that their day and night cycles would be equal in length everywhere on the planet.  I’m just going to use 10hr days and 10hr nights as arbitrary numbers, since it doesn’t really matter what I use as long as they are equal lengths.

 

Salas rises at sunset (WoK Chpt 2 & 27).

Salas sets before Nomon rises, this is the “darkest period of the night” (I-6), and it lasts about one Rosharn hour (called “the hateful hour” I-6).

Mishim rises in the east when Nomon is setting in the west (Chpt 23).

 

 

Because the times between moonrises are described so precisely, I still believe they have to be in the same orbit.  So they have the same orbital period.  However, the orbit is elliptical, which means the moons will travel faster around perigee and then slower as they reach apogee.

 

“Roshar's moons are much much closer than our moon. Their elliptical orbits bring them closer to Roshar's surface during the night than geosynchronous altitude.”

-Peter

 

 

As I said in a previous post, I’m beginning to think the lunar orbit precesses so that apogee is always towards the sun, and perigee is always away from the sun.  This means that if Salas is opposite the sun when rising, Salas is basically at perigee, and is at the full moon state.

 

Also, in order for any of the above observations to make any sense, I think the moons have to be travelling in the opposite direction as Roshar is rotating, and the moons orbit has to average out to geosynchronous, i.e. the moons need to go around Roshar exactly once per day.

 

“Each moon is in the sky only once per day and moves across the sky in a couple to a few hours. What does that tell us about their orbits?”

-Peter

 

 

Typically, when you think of a geosynchronous orbit, when when object orbits once per day, you think of an object that “hangs” in the sky (like Calamity from Steelheart).  It’s always at the same place relative to the ground, no matter what time of day it is.  But this is only when the satellite is orbiting in the same direction as the planets rotation.  If it’s moving at an overall geosynchronous orbit, but in the opposite direction of the planets rotation, then you’ll see it move…and you’ll see it move fast.

 

Here’s another poorly drawn image!  This is a view of the orbit of Roshar and its moons as seen from above looking down.  The little stick figure, for the sake of this exercise, is standing on the equator at sunset.

 

post-8393-0-19581000-1393725798_thumb.jp

 

If you were standing where the figure is in the image, you would see the sun in the western horizon.  As Roshar rotates counterclockwise the figure would be moving around the night side of the planet, and then at the top of the image of Roshar they would experience sunrise.

 

Speculation on the orbits of Salas, Nomon, and Mishim:

 

Because Salas is rising at about the same time the sun is setting, Salas must be opposite the sun, and it must be near to perigee in its full moon phase.  As Salas moves clockwise, and Roshar orbits counterclockwise, Salas would immediately begin waning.  It would be seen to set in the west in only a matter of hours, I’m guessing an hour before midnight and probably be seen as a half moon.  Salas starts bright-ish, but competing with the setting sun, and only gets dimmer as it moves across the sky.

 

Then we have to wait a bit of time, as between Salas and Nomon is “the darkest period of the night” known as “the hateful hour.”

 

Nomon would rise around midnight as a waxing gibbous moon.  Since it is midnight (and midnight in Alethkar means you’re facing directly at perigee) Nomon is moving towards the fastest part of its orbit.  It will scoot along the sky rather quickly phasing into full moon, and then slow down a bit as it passes perigee and phases out of full moon.  It would set, I’m guessing maybe 2 or 3 hours after rising, as a waning gibbous, or near half-moon.

 

While Nomon is near the western horizon, Mishim rises in the east.  Mishim would rise perhaps as a waxing half-moon.  It will move faster as it goes across the sky, and I’m thinking it would set about 2 or 3 hours after it rises.  This would mean it sets as it is near perigee and full moon phase, and about the same time as sunrise.

 

I also think the plane of the moons orbit is inclined compared to the plane of Roshar’s orbit around the sun.  If the lunar orbit was in the same plane, or near the same plane, as Roshar’s, you would get a lunar eclipse of some kind every single night.  Since there is no mention of anything like this at all, I think it’s safe to say the plane of lunar orbit must be tilted significantly.

 

Also, because Alethkar (and the whole super continent) is in the southern hemisphere (the “Frostlands” are southeast of Alethkar and the “tropical” Reshi Islands are to the north), I think the inclination of the lunar orbits is to the south at perigee and to the north at apogee.

 

In the (badly drawn and out of scale) image below, the sun is in the center, and Roshar is visualized at two opposite locations in its orbit, and the orbit would be going into and out of the page.

 

post-8393-0-54893600-1393725815_thumb.jp

 

The moons orbits would pass above the sun as seen from Roshar when they are towards the day side.  From the southern hemisphere’s perspective, if the moons were visible during the day, they would be low on the horizon.  When the moons orbit takes them to the night side of the southern hemisphere, they would be able to cross higher in the sky.

 

 

This is all leading me to other ideas, but those I would want to math out first...

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Hmm. I'm still of the opinion that the moons are not in the same orbit. The timing of the moon rise  is very specific. But as I previously stated, I don't think this is due to your Langrous point speculation, and owes more to intentional placement of these astral objects. I have no evidence beyond initial observations of the amount of light provided however.

 

Also of we take the Rosharan day of 19 hours, we get 9+1/2 hours of darkness. If Salas is in the air for 3 hours, we have 1 hour of no moonlight. That leaves us with approximately 2+3/4 hours of light for Nomon and Mishim. Would that help your math Leiyan?

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Wow, huge work you put into that!

Also, thx for the info about zero tilt, I suspected it, but didn't see a WoB on it before.

I’m beginning to think the lunar orbit precesses so that apogee is always towards the sun, and perigee is always away from the sun. This means that if Salas is opposite the sun when rising, Salas is basically at perigee, and is at the full moon state.


I agree that it's a logical conclusion from observation.
But this is a very strange phenomenon, normally impossible.

It might be caused by:
- Planet's gravity… if the speed of light was much lower (relativity magics, I don't quite get it, but my husband said it's possoble and Sun works on Mercury like that IRL, but for a planet to affect its moon in such way c wold need to be lower) – unlikely for Cosmere to have different c, I think.
- Star's gravity, with very high excentricity (like 30?) of moon's orbit it's possible. This would however make it all unstable and you can forget about any Lagrangian points… but hey, we have a future-seeing beings and gravity-affecting magics. Instability? What instability? ^^
- Generally by magic, we've seen it messing with gravity already. Some big gravityspren (hmm… it reminds me of Cusi-whatever's the name) / Jezren / Cultivation / something similarly powerful. And seeing the future or really good at maths, so probably Cultivation. Also, the question here is: why and what for would somebody do it?
 

and the moons orbit has to average out to geosynchronous, i.e. the moons need to go around Roshar exactly once per day.

I think you forget to take Roshar's rotation into account.

1/day orbit, in different orientation (I'm not sure if we can call it geosync) would mean they are visible 1 times per day (one in day and one in night) and it would be impossible for almost all night to have moonlight. Which it doesa, I believe, since the darkest time is a gap between moons, and there is no mention of another darkest hour.

 

Edit: I have no visual imagination.

What you wrote makes a full lot of sense, I think it must be right. (though still I'm not sure about calling it geosync if it's in different direction, but I agree with general idea)

With an orbit like that they already move very quick by night (in terms of angular speed).

From the southern hemisphere’s perspective, if the moons were visible during the day, they would be low on the horizon.  When the moons orbit takes them to the night side of the southern hemisphere, they would be able to cross higher in the sky.

As far as I could figure this out (by direction of sunlight, but I'm not 100% sure), Roshar continent is on southern hemisphere. I wonder why do they call it "south" then – but this is another matter…

Edited by Eri
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