Leiyan

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. >.>

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! Well, it's my first shot at this sort of thing. =) I hope you mean the flaws will become apparent in WoR?

EDIT: There's been a lot of discussion and revision to my original ideas, and I would recommend basically skipping this first post for the most part. It is, however, important to read the first two sections ("Observations" & "Related Information") as they set up some of the information given in the books and by Peter which is used to support the rest of the findings. Here are links to my most recent analysis: The orbits of the moons precess as the planet orbits the sun: http://www.17thshard.com/forum/topic/6334-the-moons-of-roshar/?p=103069 (I've since dropped the notion that they share exactly the same orbit, better language would be to say the moons share the same period and have very similar orbits....more on this in the posts below.) The orbit of the moons is in the opposite direction compared to Roshar's rotation: http://www.17thshard.com/forum/topic/6334-the-moons-of-roshar/?p=103135 (more details in the next link...) More about the orbits being in the opposite direction & how the orbits must be inclined when compared to the plane of the Roshar's orbit around its sun: http://www.17thshard.com/forum/topic/6334-the-moons-of-roshar/?p=103175 Preliminary calculations for the orbits: http://www.17thshard.com/forum/topic/6334-the-moons-of-roshar/?p=103350 There is, of course, a lot of good discussion and contributions between all these posts that I would recommend! I'm in the processes of re-organizing all of the information that has been deduced into a single document, so it can be read without the need to jump between posts and it would skip past the incorrect hypotheses. ----Orignal Opening Post (read the first two sections, the rest is now discarded)---- All this talk about the moons of Roshar in the other two threads got me thinking… Based on the "observations" provided in the book and the comments from Peter, I’ve come up with some speculations about the moons of Roshar. First…the data! Observations: “The sun set in the west, but the wagons kept rolling. Violet Salas peeked over the horizon to the east, seeming hesitant at first, as if making sure the sun had vanished.” WoK Chpt 2 “Nomon—the middle moon—had begun to rise, bathing the city in pale blue light. Staying up this late had been a rare privilege for her in her father’s house…” WoK Chpt 8 “Szeth looked over his shoulder, wishing that the Second Sister—known as Nomon to these Easterners—had risen to give a little more light.” WoK I-3 “Salas’s violet light shone in the sky outside, but the small moon wasn’t bright enough to illuminate the barn’s interior, and the creature had moved into a shadowed recess.” WoK Chpt 19 “Nomon—the middle moon—shone with his pale, blue-white light.” WoK Chpt 23 “Nomon was setting in the west, and the small green disk of Mishim—the final moon—was rising in the east.” WoK Chpt 23 “Two hours later, at Salas’s first violet light, Rock and Kaladin walked back into the lumberyard. It was just past sunset, and many of the bridgemen would soon be going to sleep.” WoK Chpt 27 “Kaladin smiled, leaning back, looking upward toward the dark sky and the large sapphire moon.” WoK Chpt 73 Related Information: PeterAhlstrom, on 06 Feb 2014 - 2:06 PM, said: 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? http://www.17thshard.com/forum/topic/5854-setting-limits-on-the-size-of-roshar-the-planet-and-roshar-the-continent/?p=94890 PeterAhlstrom, on 06 Feb 2014 - 5:15 PM, said: I expect the moons were put in their current orbits artificially, but by whom or what I do not know. On astronomical terms, these are not stable orbits, but astronomical terms means millions of years. A few thousand or even a few hundred thousand years are no problem. http://www.17thshard.com/forum/topic/5854-setting-limits-on-the-size-of-roshar-the-planet-and-roshar-the-continent/?p=94976 PeterAhlstrom, on 27 Feb 2014 - 11:37 PM, said: They are very small. Think Phobos and you'll be in the ballpark. http://www.17thshard.com/forum/topic/6249-will-we-see-interplanetarlunar-travel-in-future-books/?p=102426 ------ Here are the “facts” based on the observations: Salas and Mishim are both described as “small” moons. (WoK Chpt 19 & 23) Nomon is described as a “large” moon. (WoK Chpt 73) Salas always rises first, Nomon always rises second, and Mishim always rises third. [szeth refers to Nomon as the Second Sister (WoK 1-3), Nomon is refered to as the “middle moon” (WoK Chpt 8 & 23), and Mishim is called the “final moon” (WoK Chpt 23), by process of elimination Salas is first.] Orbital Locations of the Moons: Since the moons always rise in the same order (Salas, Nomon, Mishim), all three moons have to be the same distance away from Roshar. They all have to be in the same orbit. Otherwise they would appear in a different order on various nights over time. And this means… the moons are at Lagrangian points! The Lagrangian points are stable locations where objects can share the same orbit. Jupiter, for example, shares its orbit with asteroids at Lagrangian points 4 and 5. Using the above image to describe the Sun-Jupiter system, the Sun is at the center, Jupiter is the purple body to the right (between L1 and L2) and the Jupiter Trojan asteroids are found around L4 and L5. Lagrangian points 4 and 5 are always about 60 degrees from the body on the right (Jupiter, in this example). In the case of these moons, Roshar would be the central body, while the most massive moon (based on the size, this would presumably be Nomon) would take the purple point near L1L2 (where Jupiter was), and the other two would have to sit at the other Lagrangian points. There is one final piece of information that helps us lock down the locations of the moons: from WoK Chpt 23 it’s clearly states that Nomon is setting just as Mishim is rising, i.e. they are 180 degrees apart…on opposite sides of their orbit. For the Roshar-Nomon system I propose that Salas is at Lagrangian point 4 and Mishim is at Lagrangian point 3. In regards to the orbits of the moons not being perfect circles… Jupiter has an orbital eccentricity of about 0.049. The Earth’s eccentricity is only 0.016. Even Mars, with an eccentricity of 0.093(!!), still has trojan asteroids at its Lagrangian points. I think it’s safe to say the Roshar-Nomon system has Lagrangian points. It is, however, notable that L3 is typically a very specific point and it can be unstable…I’m hoping the “artificial placement” of these moons helps to explain how Mishim ended up in such a perfect placement. Size Approximations: Since Peter suggested Phobos was a ballpark, I’m going to go ahead and copy it as a template for the moons of Roshar. First, Phobos orbits at approximately 9000 km from Mars, so I’m going to put the Three Sisters at that distance from Roshar. Because Nomon seems to reflect enough light to see by at night (WoK Chpt 8), which our Moon does as well, and I don’t have anything better to go on, I’m going to assume that Nomon looks to be visibly the same size as our Moon. Our Moon is about .5 degrees in diameter on the night sky. An object at 9000 km away would have to be 80 km in diameter to appear as .5 degrees in diameter on the night sky. As for the small moons, I’ll look to Phobos as an example again. Phobos is 22 km in diameter. From the surface of Mars, Phobos would appear to be about .14 degrees big on the night sky. In other words, a moon the size and distance of Phobos would appear to be a little under the diameter of the Moon as seen it from Earth. Assuming that the small moons, Salas and Mishim, have relatively the same diameter and mass, and that Nomon is significantly larger, these numbers seem decently reasonable to me. It would make the two “small” moons appear to be about 1/3 the size of the “large” moon, and the “large” moon would appear similar in size to our Moon. Closing Thoughts & Questions: It’s after midnight, so I don’t want to try and figure this out now, but I think we can get some more solid information on the orbital period of the moons based on what is presented in the Observations and Information sections. Peter said the moons were in the sky “only once per day,” which is interesting.... Especially considering that all observations of the moons only seem to take place at night (anyone have any daytime references?) There are two comparisons between sunset and Salas moonrise that I can recall; WoK Chpts 2 and 27. In both chapters, Kaladin observes Salas rising just after the sun had set. 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. It is, however, clear that Noman is setting when Mishim is rising (WoK Chpt 23). If the moons are only in the sky at night (as visible from Alethkar at least), does Salas always rise just after sunset? I’d love some lunar observations from Shinovar to see if the moons are visible during the day over on that side of the world! It is also possible that the two small moons are simply too small to reflect enough light, and the large moon, being blue, might just blend in with the sky. Still it seems really really weird to me that we only have nighttime lunar observations. Something to consider! I can’t wait to read of additional lunar observations in Words of Radiance!!!!!! ((edited for ugly formatting error I didn't notice in the previews))

That works for me! =D

I'm confirmed to attend as well! Worked out a car rental, bwahaha!

Do you have anyone for the Philadelphia signing yet? I'm from (way) out of town, but as that is the nearest signing, I'm planning to trek in for it. Already have the day off of work and everything. =D

Thank you for replying! I've been trying to make some speculations about the moons, there is just so little to go on thus far. I assumed they were natural until I came across your statement about artifical placement. Very, very interesting....

Peter, any chance you could answer this question? Were the moons also artificially created, or were they originally formed naturally? edit: typos ><

I gave up on EotW about 60% of the way through my first time reading it. My friends were totally in love with the series, but I just couldn't finish the first book. So, trying to give it another shot, I picked up book two, the Great Hunt and started reading there. -That- one hooked me instantly. After I finished reading the Great Hunt, I went back to finish EothW and the went through the rest of the series.

Hai! I've been an unregistered lurker of the 17th Shard for a long long time, and a quiet member for the last several months. Like everyone else here, huge fan of Sanderson and everything he writes. I'm up in the Boston area currently, and would love to meet fans locally and (inter)nationally! I've attended JordonCon once and had a good time, but was a bit to shy to really get to know anyone. For that matter, been too shy to post here....but I want to change that and get to know other fans soo..... hello!

This is a long shot, but as I am in Boston the signing in Philadelphia is my best chance. Would anyone be interested in carpooling down from Boston? I don't have a car, but I can drive and pitch in for gas!