Humph Posted March 2, 2014 Report Share Posted March 2, 2014 Peter indicates here that there are "orbits". Note the plural. - 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? This following is currently in the status of "crackpot" theory at this point -- What if the gravitational instability of the moon system is in fact a requirement for the magic system of Roshar? I mean, we have three moons, and we have the original Great Triumvirate of Honor, Cultivation and Odium -- it's not a great leap to posit that each was responsible for the placement and subsequent activity of one moon. In other words, we don't have geography-based magic as on Sel, but we have astronomy-based magic. In other words, the gravitational stability of the moon system is generally ensured by having *somehow* [and this is the big fly in the ointment] having any rogue excess gravity in the orbital system bleed off into Roshar itself, feeding and causing the Hightstorms. In other words, in this crackpot theory, stormlight is simply a force from the spiritual realm (gravity) that has leaked into and coalesced into the physical realm (as the energy of the Highstorm and as stormlight). We can then posit a further cycle in which some of this physical energy is mutated into the cognitive realm, causing the physical expression of spren in Roshar. And then perhaps also a removal of this energy from the cognitive realm back into the spiritual realm (to keep all in balance) in some manner, perhaps by the destruction of spren and ideas (cognitive elements) via the Desolations. That would make the Desolations a requirement for the balance of the magic system in Roshar. The point of the Heralds then would be to ensure the survival of the physical and cognitive realms for the next cycle of Desolation. And perhaps this cycle is different as Honor is gone this time and his presence is required for the cycle to work properly? As I said, a bit of a crackpot theory but interesting to ponder. 3 Link to comment Share on other sites More sharing options...
bartbug Posted March 2, 2014 Report Share Posted March 2, 2014 I've always believed that the lunar cycle affects Highstorms, and maybe Desolations. In fact, I plan on asking Brandon at the San Francisco signing. 3 Link to comment Share on other sites More sharing options...
Popular Post Leiyan Posted March 2, 2014 Author Popular Post Report Share Posted March 2, 2014 Lots of good points above…thanks for helping me to keep thinking about the problem… I want to get this right. =D --- So I took a closer look at Jupiter and its trojans…What I should say is that they share the same orbital period, and they share one focus (the sun), but they have different eccentricities, and thus, yes, different orbits. Here's an example gif of 624 Hektor (in blue), orbiting the sun, with Jupiter’s orbit visualized as the large red circle. (img source: http://en.wikipedia.org/wiki/File:AnimatedOrbitOf624Hektor.gif) Both Jupiter and Hektor take 4330 Earth days to orbit the Sun, but their orbits are slightly differently shaped ellipses, because of their eccentricities. It's very likely the same thing is occurring with the moons of Roshar in their orbits. --- The amount of time something needs to complete an orbit is basically determined by the distance it is from the object it is orbiting. This is given in Kepler's Third Law of Planetary Motion: (M1 + M2)P^2 = k * a^3 M1 = the mass of the large object that is being orbited (the planet). M2 = the mass of the orbiting object (a moon). P = the period, the time the orbiting object takes to orbit the central mass. k = a constant number equal to (4(pi)^2)/G [G is Newton’s constant]. a = the distance the orbiting object is from the central point of its orbit; in the case of an ellipse it is the semi-major axis. In the case of Roshar the planet, we can determine an approximate mass from its approximate density and radius. As for the moons, we don’t really have anything to go on other than the example of Phobos, in which case the mass of each moon is negligible when compared with the mass of Roshar and can be pretty much ignored in the equation. This leaves us with only two variables: P & a. Because of this, we know that P^2 is proportional to a^3. Since we actually know what P is (1 Rosharn day, or 19 Earth hours), we can solve for a. So let’s determine the mass of Roshar… As I mentioned, we can determine this based on what we know of the density and gravity of Roshar, similar to the work done here: http://www.17thshard.com/forum/topic/5854-setting-limits-on-the-size-of-roshar-the-planet-and-roshar-the-continent/ I hate doing math in a text editor, so here’s a picture of the math where we find the mass. Please keep in mind that all units are in Earth units. End result, mass of Roshar is about 2.1x10^24 kg. For comparison the mass of Mars is much much smaller at 0.64x10^24 kg, and the mass of Earth is about three times greater at 5.97 x 10 ^24 kg. Using the mass of Roshar in Kepler’s Third Law, assuming negligible moon masses and an orbital period of 19 Earth hours, we can solve for the semi-major axis. The semi-major axis for an orbit around Roshar that takes 19 Earth hours to complete is: 25,500 km. The semi-major axis is the measurement of the distance from the center of an ellipse to one of its furthest edges. The more eccentric an orbit, the flatter and more elliptical it will be. Also, a more elliptical orbit has its focal points further from the center when compared with a less eccentric orbit. To illustrate, here is a not-to-scale computer drawing(!) of three exaggerated elliptical orbits: (eccentricities are greatly exaggerated!) As I hope you can tell from the drawing, it is intended that all three orbits share Roshar as one focal point, but their second focal points are in different locations. More importantly the center of each ellipse (shown by the vertical lines) is at a different place as well. It’s not drawn with any precision, but the distances between an ellipses’ center and the long side of that ellipse, aka the semi-major axis (shown by the horizontal grey lines) should be equal with the other two ellipses. 25,500 km each. The semi-minor axis (the distance from the center to the short side of the ellipse) varies depending on the eccentricity. If we can get information on the eccentricity or the semi-minor axis of a moon, we can solve for the elliptical orbit of that moon. 23 Link to comment Share on other sites More sharing options...
DocHoliday Posted March 3, 2014 Report Share Posted March 3, 2014 You're doing an amazing job of proving me right For real dude, Upvote for the math-fu. Link to comment Share on other sites More sharing options...
Leiyan Posted March 3, 2014 Author Report Share Posted March 3, 2014 Not trying to prove anyone right or wrong, just trying to find the best model for the system given the information we have on hand. Since there is so little to go on, and it is so scattered, it's only reasonable to have to refine as we go. I do appreciate all the input and ideas and quotes! Perhaps all this was already known..somewhere...but I didn't see any posts on it, and, well, astronomy is sorta a thing for me. Figured I'd snap up the subject while I still could! I am actually just in the middle of trying to coalesce all of the important/major points into a single document, because this thread is a bit unwieldy with the various speculations and ideas. 1 Link to comment Share on other sites More sharing options...
Satsuoni Posted March 3, 2014 Report Share Posted March 3, 2014 Roshar is not the only planet in the system, and Braize (Damnation) could be actually close enough to affect moons, though its actual position is uncertain. 2 Link to comment Share on other sites More sharing options...
Swimmingly Posted March 3, 2014 Report Share Posted March 3, 2014 This is more to do with Scadrial than Roshar, but shouldn't a single planet in two-body system have perfectly stable LG points, because you don't have any moons or other planets throwing off the balance? So the fact that the LG points on Scadrial aren't filled with debris should indicate that Scadrial isn't alone in it's star system? Of course, during the Final Empire, the sky was filled with ash and none of the main characters in AoL seem very astronomically inclined, so... Link to comment Share on other sites More sharing options...
DocHoliday Posted March 3, 2014 Report Share Posted March 3, 2014 Not trying to prove anyone right or wrong, just trying to find the best model for the system given the information we have on hand. Since there is so little to go on, and it is so scattered, it's only reasonable to have to refine as we go. I do appreciate all the input and ideas and quotes! Perhaps all this was already known..somewhere...but I didn't see any posts on it, and, well, astronomy is sorta a thing for me. Figured I'd snap up the subject while I still could! I am actually just in the middle of trying to coalesce all of the important/major points into a single document, because this thread is a bit unwieldy with the various speculations and ideas. Ah, meaning no offense, you began with an excellent discussion. I disagreed in the OP and you seem to have adopted my dissemination. I'm just riding your coat tails ( ), as you appear to have the know how to prove or disprove these ideas. Which is PERFECT. Figuring out the Cosmere ain't about who was right it wrong, but what is right and wrong. Keep up the good work. 2 Link to comment Share on other sites More sharing options...
Eri Posted March 3, 2014 Report Share Posted March 3, 2014 Roshar is not the only planet in the system, and Braize (Damnation) could be actually close enough to affect moons, though its actual position is uncertain. Are we sure that Braize = Damnation? Also, unless they have some way of syncing, planets on different orbits have different speeds, so Braize would be close to Roshar only once per some time (which may be half a year to some years, I think). Hm… Weeping? Anyway, distance between neighboring planet's orbits is millions km-scale. Moon orbits are thousands of km. Which means that even at it's closest Braize is still really far from the moons. Link to comment Share on other sites More sharing options...
Satsuoni Posted March 3, 2014 Report Share Posted March 3, 2014 Are we sure that Braize = Damnation? Also, unless they have some way of syncing, planets on different orbits have different speeds, so Braize would be close to Roshar only once per some time (which may be half a year to some years, I think). Hm… Weeping? Anyway, distance between neighboring planet's orbits is millions km-scale. Moon orbits are thousands of km. Which means that even at it's closest Braize is still really far from the moons. I am sure See my other posts for reason, if you will. And yes, you are probably right about scale, unless the moons' orbits are *really* elliptical, which is unlikely. Hmm. Just thought it was worth mentioning. Astronomy is not one of my strong points. 3 Link to comment Share on other sites More sharing options...
DocHoliday Posted March 3, 2014 Report Share Posted March 3, 2014 I am sure See my other posts for reason, if you will. And yes, you are probably right about scale, unless the moons' orbits are *really* elliptical, which is unlikely. Hmm. Just thought it was worth mentioning. Astronomy is not one of my strong points. First off, I down voted this accidentally, could someone correct? If Brayse is close enough to affect the gravitational orbit of the moons, Roshar is in big trouble. Bad enough on the million of year scale that the moons arn't geosynchronous, but if a planet is tugging those moons around as well then the problem is accelerated to a few millennia. Also there is as much evidence that Damnation is in Shadesmar as it is on Brayse (which is none). We have zero information on its location. Link to comment Share on other sites More sharing options...
luckat Posted March 3, 2014 Report Share Posted March 3, 2014 First off, I down voted this accidentally, could someone correct? Sure thing. Fixed. 1 Link to comment Share on other sites More sharing options...
ccstat Posted March 3, 2014 Report Share Posted March 3, 2014 Great analysis and discussion. I'm sorry I'm late to the party. I'm still thinking through this, Assuming three same-period-different-eccentricity orbits as posited above, what are the factors for or against them sharing the same plane? Would you expect them to have the same tilt relative to Roshar? Also, Leiyan, if you want to edit the OP with a link to the most recent version of your analysis, that might be useful for people just arriving at the thread. Link to comment Share on other sites More sharing options...
Leiyan Posted March 3, 2014 Author Report Share Posted March 3, 2014 (edited) I'm going to reply to a lot of things that were accidently left behind. I didn't mean to just skip over replies, there was just so much stuff to consider! Also, Leiyan, if you want to edit the OP with a link to the most recent version of your analysis, that might be useful for people just arriving at the thread. Good idea, Ccstat; I've done just that. I'll also post the cleaned up document when I have that finished... which will probably be next weekend. Of course, who knows what else we'll learn from WoR tomorrow... Great analysis and discussion. I'm sorry I'm late to the party. I'm still thinking through this, Assuming three same-period-different-eccentricity orbits as posited above, what are the factors for or against them sharing the same plane? Would you expect them to have the same tilt relative to Roshar? Since the moons share the same orbital period, and they have the same weird elliptical orbit that precesses in relation to the sun...I really do think they share a very similar orbit. Like the image you see in the top of this post: http://www.17thshard.com/forum/topic/6334-the-moons-of-roshar/page-2#entry103350 That animated gift is a representation of an asteroid (the blue line) that shares a similar orbit with Jupiter (the biggest red circle). They don't have the exact same orbit, but it's close. The mass difference between Jupiter and the asteroid would be much much greater than the difference of the masses between the moons, but I -think- the concept still holds. At least, I was under the impression that the moons sort of followed each other on the night sky. Though I'm not using Lagrangian points as a starting point anymore, nothing that we've come up with actaully contradicts having the moons at those places as a possibility, and if the two least massive moons were at Lagrangian points in relation to the most massive moons, they would certainly be in the same/similar plane. The lack of eclipses leads me to believe they share at least the same minimum inclination/orbital plane. But the "absence of evidence is not the evidence of absence." (it's almost a ketek!) Although if these moons never eclipse we would never read someone pointing that fact out, since it is unlikely anyone would posit the possibility of an eclipse. Did you mean the tilt of the moon's rotation? That one would be harder... It's likely the moons are tidally locked (the same side would always face Roshar, like the Moon and Earth), but I have no basis for this assumption. If they were tidally locked, and if the moons do have an inclined orbit, this might indicate a substantial tilt to the moons rotational axis. I would have to think on this some more... I would really like some observations of features on the moons over time. This is more to do with Scadrial than Roshar, but shouldn't a single planet in two-body system have perfectly stable LG points, because you don't have any moons or other planets throwing off the balance? So the fact that the LG points on Scadrial aren't filled with debris should indicate that Scadrial isn't alone in it's star system? Of course, during the Final Empire, the sky was filled with ash and none of the main characters in AoL seem very astronomically inclined, so... Well, a planet in a multi-planet system has stable Lagrangian points (points L4 and L5). You can look at Mars, Jupiter, Neptune...I think it was even discovered that Earth has some trojan asteroids hanging out in a Lagrangian point. In fact two moons of Saturn have other moons in their Lagrangian L4 and L5 points (last line in both http://nineplanets.org/tethys.html & http://nineplanets.org/dione.html). All of this is to say that having or not having stuff in a Lagrangian point is not proof of the existence or non-existence of other gravitational objects in a system. BTW does anyone know how hich eccentricity (of moon's orbit, not planet's) affect Lagrangian points? I couldn't find in on Google. Eri, over the weekend I found a couple of articles that might talk about this. I haven't had a chance to read them yet (and I won't for a few days at least) to see if they can help answer the question for us, but I'll post if/when I get any more information. I'm curious about this as well! What I can tell you off hand is that Mars has an eccentricity of 0.0934 (which is actually pretty high for a planet) and it has objects at it's Lagrangian points. Roshar is not the only planet in the system, and Braize (Damnation) could be actually close enough to affect moons, though its actual position is uncertain. As other have already covered, if Braize was close enough to strongly affect the moons of Roshar, it would be close enough to strongly affect the planet of Roshar. I've always believed that the lunar cycle affects Highstorms, and maybe Desolations. In fact, I plan on asking Brandon at the San Francisco signing. Hmmm.... Well, the moons orbit every day, but you don't get highstorms every day, right? Although, perhaps the orbits of the moons cause a resonance? Like in a tub if you splash, and then splash again at just the right moment, the waves add up to make a bigger wave... Interesting... 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? I was attempting to guess at the number of hours in a Rosharn day, but it was probably a bad idea because it confused the issue. 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. I didn't respond to this directly before, but I think this was sort of addressed when I was speculating on the lunar phases. Nomon would probably start out as less than full moon and then move towards full moon (and thus be brighter) as it rose, then start waning again as it moved to moonset. Both Salas and Mishim are described in the text as "small" while Nomon is described as "large", meaning this is how they appear visibly. Kaladin gave the size description for Mishim and Nomon, while Dalinar is who Salas's size description is from. Still, I think they would relatively the same idea of what a "large" or "small" moon would be like, and I would trust that Salas and Nomon do have a fairly significant apparent size difference. All that being said, the apparent size calculations I gave were mostly guess work and supposition. Edited March 3, 2014 by Leiyan Link to comment Share on other sites More sharing options...
king of nowhere Posted March 4, 2014 Report Share Posted March 4, 2014 I see no one mentioning it, but since the moons orbit in an opposite sense to roshar rotation, that means that they have an orbital period of one rosharan day, which summed with roshar's rotation means they will make a tour around roshar twice during a rosharan day (considering the surface of roshar as a still reference system). that is consistent with all the other facts we have. if they had a greater orbital speed and made 3 or 4 or more rounds every day, they would appear more than once per night. instead with an apparent time of half a day they stay in the sky one per night and once per day, but during the day the sun is too bright and covers them up; also, they are much farther from the planet. people standing on the opposite side of the planet would still see the moons going up each night, but they would seem smaller, and they would probably be visible at all times since they would be in the larger part of the eclypse. Furthermore, they have all the same orbital period, but the ellypses may have different orientations. About the moons causing the highstorms with gravitation influence, I would rule it out. They are small moons, basically they are rocks two or three times the size of mount everest. which is pretty big as a mountain, but nowhere near big enough to make a significant influence on the gravitational field. You don't see water rising in the sky on the coast of india because of the gravitational attraction of the hymalaia range, which is bigger and closer than the rosharan's moons. For those we can estimate a distance from the planet of no less than 10 thousands kilometers at the perigee (25000 km is a reasonable guess for major semiaxis, roshar's density is unknown but unlikely to produce a big error, and it would take a really huge eccentricity to have a closer apogee than that). If there is an influence of moons on the highstorms, it is mystical, not physical. AS for braize, it may be on another orbit, in which case even at its closest would be a few tens of millions of km from roshar, too far to exert a significant gravitational influence, or it is in a lagrangian point with roshar, in which case it is always the same distance. this second hypotesis is more likely, cause if braize was in a different orbit, then it would likely be too hot or too cold to support life (not necessarily however: mars is colder than earth, but still warm enough that it could support life around the equator. if it had enough gravity to keep water and a thicker atmosphere). I'm now wondering at the composition of the moons. those colors aren't natural, and I can't think of many substances that give those kind of colors. certainly not substances that come naturally in phobos-sized blocks. they were crafted specifically to have those colors. I wonder what actually possessed a shard to craf some giant rocks of unusual composition and put them in those highly unlikely orbits, knowing that withing a few million years at most they would destabilize enough to crash on the surface. what's the purpose of that? Wait, totally crackpot theory: the moons are actually really big spren. that would justify their color and the fact that they follow odd orbits. It would also justify that they seem to have some mystical significance that cannot be explained with physical phenomenon. That's all I can think for now. Sorry if my explanations are a bit confusing at times; normally I have no problem expressing myself in english, but for this specific argument I did. 1 Link to comment Share on other sites More sharing options...
Eri Posted March 4, 2014 Report Share Posted March 4, 2014 I'm now wondering at the composition of the moons. those colors aren't natural, and I can't think of many substances that give those kind of colors. Maybe they are giant gems? Link to comment Share on other sites More sharing options...
HydrogenAlpha Posted March 5, 2014 Report Share Posted March 5, 2014 I still think there's no better place for hiding a shardpool than on a moon ! Link to comment Share on other sites More sharing options...
Battar Posted November 10, 2015 Report Share Posted November 10, 2015 Are there any updates in Words of Radiance that gave us more information about the moons? Link to comment Share on other sites More sharing options...
ARARITA Posted November 11, 2015 Report Share Posted November 11, 2015 I was thinking 2 moons and 1 artificial object (spaceship) but the whole spren thing is awesome great post Link to comment Share on other sites More sharing options...
Melriken Posted November 11, 2015 Report Share Posted November 11, 2015 A year on Roshar is 500 days, the time between weepings, every other weeping has a single highstorm, the rest don't. Those highstorms are on the same day (1000 days apart). The sun goes up and down, so a day is the rotational speed of the planet adjusted for it's orbital speed, however the planet has a zero tilt rotation, so there are no seasons to mark the passing of the year. Further there is no deep ocean travel to require astronomical navigation. I know we have a set of red stars and a single bright star but do we actually have enough information to confirm that a year is one orbit around the sun? Does Roshar orbit it's sun every 1000 days? Every 50? Something else? The Taln's Scar's position on your 7th birthday is important... But that means that the Scars position is different on your 7th birthday then it is on your other birthdays. Which means it is either a local collection of objects (in the Roshar system) and moves independent of Roshar's solar orbit, or that Roshar's orbital period is NOT 500 days (or 50 or any other exact count of days that goes into 500). Does this alter the moon's orbits? Potentially it lets some VERY crazy things happen but probably not, it just came about because of thoughts of the moons 2 Link to comment Share on other sites More sharing options...
Melriken Posted November 11, 2015 Report Share Posted November 11, 2015 Actually without axial tilt the stars wouldn't move at all, would the locals have any way to measure an orbit of the sun at all? Is there any way for us to tell from the text what a true year is? Link to comment Share on other sites More sharing options...
skaa Posted November 11, 2015 Report Share Posted November 11, 2015 (edited) Actually without axial tilt the stars wouldn't move at all, would the locals have any way to measure an orbit of the sun at all? Is there any way for us to tell from the text what a true year is? The cycle of weather patterns on Roshar have been regular enough that they can be used the same way we use astronomical data to define the year. On Roshar, the year ends on the Weeping, the four weeks of light rain that marks the end of the cycle. Edit: Ignore what I wrote above. I should have read Melriken's longer post first. I failed to see the context of his shorter post before replying. Sorry about that. By the way, Melriken, this is why double-posting is often a bad idea. Please just edit your post next time. Edited November 12, 2015 by skaa 1 Link to comment Share on other sites More sharing options...
KnightGradient Posted November 11, 2015 Report Share Posted November 11, 2015 From what I can tell in the books, Rosharan astronomy isn't as important as it was on Earth. On Earth, astronomy was a major science when our lifespans were 25(Stonehenge is an example of this). On Earth, that was how you would know when winter was coming(Sorry I Starked out for a bit). On Roshar, seasons aren't very important, and highstorms are the most regular event, always ending the cycle with a long Weeping. So Roshar has medieval meteorology, instead of inventing the telescope. So, Rosharan astronomy is millenia behind Earth's. 1 Link to comment Share on other sites More sharing options...
Melriken Posted November 12, 2015 Report Share Posted November 12, 2015 (edited) I double posted because there was no edit button, likely because I am using the mobile version of the site. Also the stars would be the same year round but which portion you see at any given time of the day would shift (noon's sky would be midnight's sky half a solar orbit later) but the natives may not have realized this as solar orbits don't matter much to them. Edit: found the edit button on the mobile site, it is hidden. Edited November 12, 2015 by Melriken Link to comment Share on other sites More sharing options...
ARARITA Posted November 12, 2015 Report Share Posted November 12, 2015 I remember seeing that Brandon wanted something like Jupiter's Great Red Spot so ... I looked up "moons of Jupiter" - found a wiki on it talks about irregular satellites I don't have any working knowledge of astronomy / orbits etc there is a link in the wiki that goes to "secular resonance" which has a link to "orbital resonance" which I am hoping will help someone with working knowledge Link to comment Share on other sites More sharing options...
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