Moons of Roshar

[iohn he/him]

Does anybody know the pattern of the moons? I'm re-reading WoR currently and I got to a part where Shallan is studying in Sebarials manor and Pattern notes that she normally sleeps during the second moon, or something along those lines. Does that mean that Nomon is in a geosynchronous orbit, so its always up at the same time of day (or rather, night in this case)? I'm just curious if anybody has looked into it and/or asked Brandon about it.

[The One Who Connects he/him]

51 minutes ago, iohn said:

Does anybody know the pattern of the moons? I'm re-reading WoR currently and I got to a part where Shallan is studying in Sebarials manor and Pattern notes that she normally sleeps during the second moon, or something along those lines. Does that mean that Nomon is in a geosynchronous orbit, so its always up at the same time of day (or rather, night in this case)? I'm just curious if anybody has looked into it and/or asked Brandon about it.

We know... a couple things, but not what you're asking about yet.

Quote

Brandon Sanderson

All three moons are much closer than our moon is.

Leiyan

How big is Nomon on the night sky, like compared to our moon?

Brandon Sanderson

Larger than our moon, but not dominating of the sky. [...] I do believe Nomon is bigger, but I had to have Peter run those calculations, so he may come back and say "no Brandon, that's not possible," but I do believe it's bigger than our moon in the sky. You're supposed to be able to see moderately well by Nomon.

Leiyan

So I had some things I figured out, I just wanted to know if they're true or not. So I have that the orbits of the moons would precess so that the farthest point is always pointing towards the sun.

Brandon Sanderson

So, one more time.

Leiyan

[uses diagram to explain the question]

Brandon Sanderson

So, we have figured all this out. It's in the wiki--so me just saying--it's not in the wiki that you can find. I would need to go compare this. All the calculations on things like this--this is stuff where I sat down with Peter, who knows much more astronomy than me and said "here's what I want" and he's like "well it has to be this" and I put that in.

Leiyan

Do you know, do the moons orbit the opposite direction to Roshar's rotation?

Brandon Sanderson

I believe they do but I'm not 100% sure.

Leiyan

There are no eclipses as far as I can tell, so the plane of the orbit must be strongly inclined, 'cause there'd be an eclipse every day if there were eclipses-

Brandon Sanderson

We had to fudge that because as you said, if there were any it'd be all the time.

Brandon and Peter know many things about it, but it's a complex issue that Brandon doesn't just remember off the top of his head.

Quote

Mason Wheeler

OK. Now, the Weeping that happens each year on Roshar, does that occur each time when the 3 moons are in a particular alignment?

Brandon Sanderson

no, it's more related to the planet's orbital position than the moons' position.

The Second WoB is mostly here because it means we can't use the Weeping as a pattern point for the moon orbits.

[Landis963 he/him]

If Nomon (or any of Roshar's moons, for that matter) were in a geosynchronous orbit with Roshar, that would mean it would never deviate from its position (i.e. it would never rise, nor set, nor do anything but hang there).  Arcanum Unbounded has a pretty good diagram of all three moons' orbits, and they happen to be overlapping ellipses.  

[Wreith he/him]

1 hour ago, Landis963 said:

If Nomon (or any of Roshar's moons, for that matter) were in a geosynchronous orbit with Roshar, that would mean it would never deviate from its position (i.e. it would never rise, nor set, nor do anything but hang there).  Arcanum Unbounded has a pretty good diagram of all three moons' orbits, and they happen to be overlapping ellipses.  

That's the difference between geosynchronous and geostationary.

geosynchronous : an orbit takes the same time as the planets rotation

geostationary: orbiting body appears stationary because it's orbit matches the planets rotation exactly.

 

stationary is a subclass of synchronous. It's part of why the "do they orbit opposite of Roshar's rotation" is a worthwhile question

[CaptainRyan he/him]

1 hour ago, Wreith said:

That's the difference between geosynchronous and geostationary.

geosynchronous : an orbit takes the same time as the planets rotation

geostationary: orbiting body appears stationary because it's orbit matches the planets rotation exactly.

 

stationary is a subclass of synchronous. It's part of why the "do they orbit opposite of Roshar's rotation" is a worthwhile question

So, if I understand you correctly, a moon that orbits in the opposite direction of Roshar's rotation but does so in the same amount of time as Roshar's rotation would be geosynchronous but not geostationary?

[Wreith he/him]

yes. Like a satellite that takes 24 hours to orbit earth, but does so opposite its rotation.

 

Doesn't really do anything for the theory, but I thought it needed to be clarified.

also, this is just the knowledge of a person with astronomical interest, not an expert.

Edited October 2, 2017 by Wreith

[iohn he/him]

you're right i was thinking about that wrong, i didn't mean geosychronous. is there a moon orbit where it appears in the sky at the same time every day? In WoR, chapter 60, Veil Walks, Shallan is in her room in Sebarial's manor researching and Pattern makes the comment, "It is second moon. Each night, you sleep during this time. But not tonight." I suppose second moon could be a time of day and not actually reference when a moon is in the sky, but i it does reference when the second moon is in the sky, and Shallan normally sleeps at that time, that indicates that the second moon is visible in the sky at the same time every night. Maybe its like a crazy fast orbit, so the moon is actually orbiting Roshar fast enough that it arrives in the same spot in the sky every night. I guess that would mean it would have to orbit twice as quickly as the planet spins?

[Wreith he/him]

I read this thread quite a while ago and don't really remember if it answers the question you're proposing, but it might help

 

[iohn he/him]

Thanks @Wreith, thats exactly the info i was looking for. Granted I really should just go look in Archanum Unbounded apparently, but that's all the way at home, so i'll do that later.