Polar view of the planet

[Johnny Silverlight]

One very important fact that we're currently lacking is the density of these moons. I have a gut feeling that these "moons" are not masses of rock like most natural planetary satellites in our solar system. I think they are actually enormous living organisms of some kind that are secreting these waterfalls of spores as part of their biological process.

If they are living creatures, then their density would probably not be anywhere near as great as it would be if they were composed of rock. Another fact we're not sure about is how far from the surface of Tress's World these moons are. The Lunagrees come across, in the text, like gigantic waterfalls of spores. For this effect to occur, the moons must be very close to the planet's surface so that the planet's gravity can pull the spores down in this manner. They also cannot be too far outside the planet's atmosphere, because I can't see how the spores could pour down they way they do if they have to travel any significant distance though the vacuum of outer space.

[+Oltux72 he/him]

1 hour ago, Johnny Silverlight said:

If they are living creatures, then their density would probably not be anywhere near as great as it would be if they were composed of rock

Living organisms on Earth have a density roughly like water around 1000 kg/m^3. Rock is about three times as dense. Terrestial planets as a whole are a bit denser because they have a compressed metal core.

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Another fact we're not sure about is how far from the surface of Tress's World these moons are. The Lunagrees come across, in the text, like gigantic waterfalls of spores. For this effect to occur, the moons must be very close to the planet's surface so that the planet's gravity can pull the spores down in this manner.

Most importantly, they must not be in orbit. We do not know whether the aethers employ an active mechanism to get the spores to the planet.

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They also cannot be too far outside the planet's atmosphere, because I can't see how the spores could pour down they way they do if they have to travel any significant distance though the vacuum of outer space.

For that work you'd have to put the moons insanely low. EDIT:
Insanely low meas that you'd plung the area directly under the moon into night for a lot of the planetary day if we go with a moon covering a third of the sky. It would be more than a third of the energy being lost, as it would block the sun when it were straight up in the sky. We are talking about shielding about half the light.
In order to get the places under the moons to a decent climate you'd have to bake the rest of the planet. The resulting winds would be insane. She'd be living in a permanent hurricane

Edited March 7, 2022 by Oltux72
consequences of too low an orbit

[cometaryorbit]

22 hours ago, LewsTherinTelescope said:

He mentions that "one of the twelve is always visible, no matter where you travel", which I took to indicate that they're not just on the equator, but it's not really certain

Yeah. I suppose it's possible that the "known" or "civilized" world is all limited to relatively near equatorial latitudes, where the Aether spores are, and the rest of the planet is not really known.

[LewsTherinTelescope]

On 3/7/2022 at 2:42 AM, Oltux72 said:

For that work you'd have to put the moons insanely low

The text does specifically call them "oppressively low" fwiw, but that's... vague as hell lmao

[cometaryorbit]

Yeah. If they are in an actual geosynchronous orbit, though, that does set what the altitude can be. We can't know exactly, since we don't know the mass or day length of Tress's planet, but from Arcanum Unbounded it looks like the habitable planets in the Cosmere are generally reasonably close to Earth size and properties (Sel is like 1.5x size, Roshar is 0.7x gravity, but we don't see like Jupiter sized or Pluto sized habitable planets).

For Earth, geosynchronous orbit is a bit less than 1/10 the distance to our Moon (~23,000 miles vs about 250,000 miles) so that could be seen as "oppressively low" especially if they are large moons.

(Mars' inner moon, Phobos, is actually below synchronous orbit altitude for Mars - but it's a tiny moon. Interestingly, like Roshar's moons, its orbit is not stable over the lifetime of the Solar System - IIRC it would be expected to decay in 20-50 million years.)

[Ixthos he/him]

Brandon has confirmed that, baring feedback from his science contacts, he intends the planet and the moons to be related like the faces of a duodecahedron (or vertices of a icosahedron), which was my alternative suggestion, though that definitely would mean they are held in place rather than orbiting, perhaps with each effectively "lashed" to a point on the axis the planet rotates around, much like how Windrunners can redefine where gravity is pulling them. I'd like to do an updated take on this later to get a better feel, though I will assume the 1/3 is more poetic and accounts for the arc rather than the solid area taken up. That probably will be a while away though.

[+Oltux72 he/him]

37 minutes ago, Ixthos said:

Brandon has confirmed that, baring feedback from his science contacts, he intends the planet and the moons to be related like the faces of a duodecahedron (or vertices of a icosahedron), which was my alternative suggestion, though that definitely would mean they are held in place rather than orbiting, perhaps with each effectively "lashed" to a point on the axis the planet rotates around, much like how Windrunners can redefine where gravity is pulling them. I'd like to do an updated take on this later to get a better feel, though I will assume the 1/3 is more poetic and accounts for the arc rather than the solid area taken up. That probably will be a while away though.

Note that this also kills the equatorial band of spore oceans theory of the water cycle and that solution to the fish problem. Indeed it means most of the world's oceans, if not all, must be spores.

I would hope for these answers to be included in the Ars Arcanum.

[Ixthos he/him]

33 minutes ago, Oltux72 said:

Note that this also kills the equatorial band of spore oceans theory of the water cycle and that solution to the fish problem. Indeed it means most of the world's oceans, if not all, must be spores.

I would hope for these answers to be included in the Ars Arcanum.

Indeed! Though we may not have to throw away all our assumptions. It could also be that the creatures Hoid is describing, when not said by a character in world, are ones the listeners would know but not necessarily Tress's people (so the seal example could be entirely for the listener's benefit, rather than a comparison one of Tress's people would make). Likewise, depending on how the twelve moons are arranged, the Verdant moon may have an equatorial orbit, or one sufficiently close that, for example, the sun passes through it like a cord rather than through the centre, so the moon is slightly offset from the equator but still close enough that it does cover it - and that is assuming Tress's island is on the equator as well. 

I am interested to see how the water cycle works though, considering Brandon hinted that the book contains a scene with rain falling on the ocean.

[+Oltux72 he/him]

7 minutes ago, Ixthos said:

Indeed! Though we may not have to throw away all our assumptions. It could also be that the creatures Hoid is describing, when not said by a character in world, are ones the listeners would know but not necessarily Tress's people (so the seal example could be entirely for the listener's benefit, rather than a comparison one of Tress's people would make). Likewise, depending on how the twelve moons are arranged, the Verdant moon may have an equatorial orbit, or one sufficiently close that, for example, the sun passes through it like a cord rather than through the centre, so the moon is slightly offset from the equator but still close enough that it does cover it - and that is assuming Tress's island is on the equator as well.

If a moon is to fill a third of the arc, it will fill the space between the 60° angles at the lunagri. Hence if you are more than 30° + axial tilt away from the equator, no eclipses.

[Ixthos he/him]

Just now, Oltux72 said:

If a moon is to fill a third of the arc, it will fill the space between the 60° angles at the lunagri. Hence if you are more than 30° + axial tilt away from the equator, no eclipses.

True, but again that means she doesn't have to be exactly on the equator, and so there is a range of possible locations she could be on that have this effect, and we are also accounting for this being a regional thing, that not everywhere on the planet is subject to these sorts of eclipses.

[+Oltux72 he/him]

6 minutes ago, Ixthos said:

True, but again that means she doesn't have to be exactly on the equator, and so there is a range of possible locations she could be on that have this effect, and we are also accounting for this being a regional thing, that not everywhere on the planet is subject to these sorts of eclipses.

Very few places are. You cannot, as many people would probly do, place a vortex of the icosaeder on the poles and get these eclipses. And I see no way you can get more than three vortices on a great circle with an icosaeder.

[Ixthos he/him]

2 minutes ago, Oltux72 said:

Very few places are. You cannot, as many people would probly do, place a vortex of the icosaeder on the poles and get these eclipses. And I see no way you can get more than three vortices on a great circle with an icosaeder.

I know you meant vertex, but now I'm picturing miniature Highstorms racing around the Lunagree's on Lumar 

Depending on how many moons are visible at a time from any given location, I imagine there likely are more than three locations where this is possible - consider how the Sun traces a path through the sky, if at any point in that path it intersects a portion (not the whole) of the disc of one of those moons there will be a brief eclipse. Depending on where you are on the Earth the Sun can trace a path directly overhead, or just peak above the horizon - this is consistent across lines of latitude, but with twelve objects in the sky there are many areas which likely have at least one moon intersecting them, depending on how close the moons are and their size.

Either way, all that matters is Tress's home island is at one of those locations at least some time during the year, as perhaps at different times of the year they don't have any of these moonshadows, but at others they do. We'll just have to see how Brandon addresses this, and hopefully the Ars Arcanum as you suggested.

[+Oltux72 he/him]

16 minutes ago, Ixthos said:

I know you meant vertex, but now I'm picturing miniature Highstorms racing around the Lunagree's on Lumar 

My apologies. But now that you mention it, I need to state it. There most likely are exactly such storms. A third of the sky as arc means that at the equinoctes on the equator the sun will be blocked for a third of the day. And the hottest part of the day around noon. We are talking about losing about half of the solar energy. There will be storms.

16 minutes ago, Ixthos said:

Depending on how many moons are visible at a time from any given location, I imagine there likely are more than three locations where this is possible - consider how the Sun traces a path through the sky, if at any point in that path it intersects a portion (not the whole) of the disc of one of those moons there will be a brief eclipse.

The dihedral angle in an icosahedron is listed as 138.190°. I do not see a way for more than one eclipse per place and day.

16 minutes ago, Ixthos said:

Depending on where you are on the Earth the Sun can trace a path directly overhead, or just peak above the horizon - this is consistent across lines of latitude, but with twelve objects in the sky there are many areas which likely have at least one moon intersecting them, depending on how close the moons are and their size.

At 1/3 of the sky they are very, very close.

16 minutes ago, Ixthos said:

Either way, all that matters is Tress's home island is at one of those locations at least some time during the year, as perhaps at different times of the year they don't have any of these moonshadows, but at others they do. We'll just have to see how Brandon addresses this, and hopefully the Ars Arcanum as you suggested.

Indeed

[Ixthos he/him]

9 minutes ago, Oltux72 said:

My apologies. But now that you mention it, I need to state it. There most likely are exactly such storms. A third of the sky as arc means that at the equinoctes on the equator the sun will be blocked for a third of the day. And the hottest part of the day around noon. We are talking about losing about half of the solar energy. There will be storms.

Fair enough, and agreed. Unless they cast a very small shadow they will have a massive impact on the planet's temperature.

 

10 minutes ago, Oltux72 said:

The dihedral angle in an icosahedron is listed as 138.190°. I do not see a way for more than one eclipse per place and day.

If the icosahedron is instead positioned not with one vertex at the pole, but with three spaced evenly around it then the positions change, and the six "middle" vertices will be closer to the equator. Though even if they aren't we do still have the fallback of this being only in one or two zones, and Tress's island is in one of them.

 

12 minutes ago, Oltux72 said:

At 1/3 of the sky they are very, very close.

Agreed. One of the only options I can see for Brandon is to make them take up less of the sky, though again that would also limit the number of places that can have moonshadows regularly. The moon, which some cultures worship, is only 0.5 degrees - if you stick our hand out to its full extent and looked at your pinkie nail THAT is how big the Earth's moon Luna is - and the Sun - but they both are still deeply significant to us. If the Moons took up 1/4 of the arc, or 1/12 of the arc, that would still be impressive.

 

15 minutes ago, Oltux72 said:

Indeed

Should ... should I be worried?