Mapmaking and landscapes

[Basillicum]

Hi there!

I'm currently working on a Pathfinder-based setting where I'm leaving very little up to conventional truths. Obviously this complicates everything somewhat, but I like that.

Firstly, this world's calendar has only nine months and three seasons - Summer, High Summer and Fall. High Summer consists of only one month, but throughout this month there are two suns in the sky, whereas the extra "sun" is a smaller gas planet orbiting another solar system. As far as I can understand, this should cause the sea levels to rise, but to what extent should they do that? Should I include frequent natural disasters as well? I'm definitely open to the argument "this world is magic; I ain't gonna need to explain shit," but I'd love to expand on the idea of two suns.

If sea levels rise and fall dramatically, I think countries and settlements would have to be built especially for the High Summer-state of the world. But concerning the natural landscapes, should mountains and other heightened areas be generally taller or shorter than what you could normally expect?

Anything else in particular that I have to keep in mind in a world like this?

Input and ideas will be of great help. :)

[uriel222]

My advice? Don't worry about it. Just put in what you want, and let someone else figure out why it is that way.

[Nuclearsunburn]

This would be a question to put to an astrophysicist, if you know one. I'm sure you could find one that plays RPGs as well, it seems like the two would have some overlap :) They'll probably want to know distances, etc. Also, if you're going to have another planet close enough to be in the sky as large as the sun, it's probably going to exert enough gravitational pull to pull your planet out of its orbit. Of course, that's where you can come up with some fascinating mythology of why this doesn't happen, maybe there's an enslaved god tasked with exerting its divine power to keep your world in its orbit, or what have you (much like Atlas holding up the Earth). If you haven't already checked it out, the Paizo supplement "Distant Worlds" is an awesome imagination kickstarter for this kind of thing. It's probably my favorite PFCS supplement. I immediately thought of the world Triaxus reading your description, it's unique in the same way your world is too. I always thought it would be an awesome place to set a campaign if Golarion ever got to be too stale for me.

[GralphidB]

I'm an astrophysicist (at least, I'm in the process of getting a PhD in astrophysics), so here's my advice/comments.

-You said the gas giant is in a separate solar system. If that's what you meant to say, then it's not going to be significant, in terms of light or gravity.

If you meant the gas giant is in the same solar system, it depends on mass and size. The only thing I could think is if it's a really big giant really close to its host star, it could be reasonably hot/bright, but even then not that significant. As an really generous upper limit, a gas giant twice the radius of Jupiter and as hot as the sun would still produce only about 5% the light that the sun does. But to do this, it would have to be incredibly close to the star, and thus wouldn't be particularly noticeable gravitationally or even visibly, since it would always appear very close to the sun.

It might be helpful to figure out what results on the planet you really want and then try and determine the orbital stuff accordingly, or figure out the exact orbit, and then figure out the results. I might be able to help, sounds like fun.

If you just want hot for a while, then warm, then cool, you could do that just with a highly elliptical orbit. This will bring do a lot of what you described I think. During the "high summer" you'd be closer to the host star, which could create seasons by itself. You'd probably want a coolish red dwarf star to prevent completely frying the world when you're closer in. This would also have high summer be shorter than summer which is shorter than fall, since when the planet is closer to the star, it goes faster.

[Nuclearsunburn]

Oh wow we lured a soon-to-be astrophysicist out of the woodwork!! I'm really glad I dotted this thread! For some reason, I was picturing the sky being like Pandora, from Avatar, which I guess is a moon orbiting a gas giant. Maybe one with a strange orbit that takes it varying degrees of distance from this star (probably a red dwarf like you said) and in a fantasy setting there are any number of reasons that could be. The possibilities for epic stories abound here.

@ GralphidB I'm curious about the OP's questions about tides and terrain. I'm sure the tides would be greatly affected but what about the terrain? Would a planet subject to those kinds of gravitational swings be any more or less mountainous than another?

[Basillicum]

GralphidB wrote:

(...)

It might be helpful to figure out what results on the planet you really want and then try and determine the orbital stuff accordingly, or figure out the exact orbit, and then figure out the results. I might be able to help, sounds like fun.

If you just want hot for a while, then warm, then cool, you could do that just with a highly elliptical orbit. This will bring do a lot of what you described I think. During the "high summer" you'd be closer to the host star, which could create seasons by itself. You'd probably want a coolish red dwarf star to prevent completely frying the world when you're closer in. This would also have high summer be shorter than summer which is shorter than fall, since when the planet is closer to the star, it goes faster.

A highly elliptical orbit sounds quite good, as I've already decided that Summer lasts three months, High Summer one month, while Fall lasts five months, which fits perfectly with what you describe.

However, I wanted the gas giant to be the main reason that High Summer was significantly hotter than the other seasons, which is the reason my initial thought was to make the gas giant a part of a separate solar system, with its orbit stretching wide enough to "visit" my world, but I realise this is highly unrealistic.

If I use an elliptical orbit, could I say the the gas giant has a decidedly larger orbit but moves faster, while my own world maintains an orbit which doesn't necessarily take it very much closer to the host sun during the High Summer?

When mentioning the red dwarf, do you mean it could work as an alternative to the gas planet?

All of this is awesome input btw, thank you! I didn't expect to find an actual astrophysicist. :D

Nuclearsunburn wrote:

(...) and in a fantasy setting there are any number of reasons that could be. The possibilities for epic stories abound here.

I've thought a little about this, and found a potential storyline reason for the existence of the "second sun". :) Possibly I could use the story as an argument that the sun functions exactly how I want it to.

[Chemlak]

My astrophysics days are a long way behind me (got my degree in 97) so this is more a proposal to Gralphid: binary system, normal star and brown dwarf, with a gas giant cycling between the two of them, and the campaign world circling the normal star?

[GralphidB]

Nuclearsunburn wrote:

@ GralphidB I'm curious about the OP's questions about tides and terrain. I'm sure the tides would be greatly affected but what about the terrain? Would a planet subject to those kinds of gravitational swings be any more or less mountainous than another?

I'm an astrophysicist, not a geologist, so I'm not incredibly qualified to answer this question, but I do know that in moons around gas giants, the extra tides can cause increased internal heating of the planet, which would create volcanoes and the like. Not sure about what it would do to continental drift and regular mountains, if anything.

Basillicum wrote:

A highly elliptical orbit sounds quite good, as I've already decided that Summer lasts three months, High Summer one month, while Fall lasts five months, which fits perfectly with what you describe.

However, I wanted the gas giant to be the main reason that High Summer was significantly hotter than the other seasons, which is the reason my initial thought was to make the gas giant a part of a separate solar system, with its orbit stretching wide enough to "visit" my world, but I realise this is highly unrealistic.

If I use an elliptical orbit, could I say the the gas giant has a decidedly larger orbit but moves faster, while my own world maintains an orbit which doesn't necessarily take it very much closer to the host sun during the High Summer?

When mentioning the red dwarf, do you mean it could work as an alternative to the gas planet?

All of this is awesome input btw, thank you! I didn't expect to find an actual astrophysicist. :D

The real problem with the gas giant is it just doesn't provide that much light to be significant in illuminating your planet. It could provide heating if you were orbiting it closely, but wouldn't provide anything close to daylight

So the time for one complete orbit is directly proportional to the average distance to the star . So if the gas giant is farther from the star, it will move slower (magic not-withstanding). The orbit is also proportional to the mass of the star, so if you have a shorter year (9 months) around a sun like our star would bring it considerably closer and you'd get a venus like environment. So the star would need to colder (redder) than our sun.

However, if you really want there to be at least sometimes two suns in the sky, then you need some form of three body system, either a binary star, or your "planet" is actually a moon orbiting around a gas giant orbiting a star. The problem with this is that it results in a very limited set of stable orbits, none of which would provide what you want.

Chemlak wrote:

My astrophysics days are a long way behind me (got my degree in 97) so this is more a proposal to Gralphid: binary system, normal star and brown dwarf, with a gas giant cycling between the two of them, and the campaign world circling the normal star?

That's actually a decent idea. However, the orbit where the gas giant gets passed back and forth isn't naturally stable.

Ok, so here's some ideas:
1. The "planet" is really a moon, orbiting a gas giant with a highly eccentric orbit. In fall, it's far enough away from the sun that the sun isn't incredibly obvious (it's a pretty bright star, probably as bright as the full moon). The world is pretty dark 24 hours, but a reasonably thick atmosphere and tidal heating keeps it from getting TOO cold. In the summer, you swing close to the star, which provides additional heating and light.

2. Same as before, but you orbit a small red dwarf star rather than a gas giant. This helps fix the light problem, while still getting everything else.

3. If you want to be really crazy: A triple system of star, small star, black hole. The planet orbits close to the small star, which orbits in a figure eight back and forth between star and black hole/neutron star. Around black hole its "winter" and around star its high summer, and in between is fall. A deity level power keeps this stable (since it wouldn't be naturally). The people on the world wouldn't necessarily know the black hole even exists, since it's black.

I know none of them have a gas giant coming in to the system to provide extra heating, but I can't come up with any way of accomplishing that. The problem is a planet will only be relevant to heating/lighting if it's VERY close to you (ie you're orbiting it). Because its a planet, it's brightness depends on how close to the sun it gets, but the closer to the sun it gets, the less relevant it is, since the sun will always be at least a hundred times brighter than it.

glad to be of what help I can, it's combining three of my favorite hobbies (roleplaying, astronomy, and being a smart-ass) :-)

[Chemlak]

I'm currently wondering if a highly elliptical very small second star (so, a binary system) with perihelion, say, .75 AU, inclined to 10-15 degrees from the ecliptic, aphelion around 4-5 AU. If it's dim enough it won't be too bright an object in the sky, and orbital crossover risk will be negligible to nonexistent.

Just tossing out ideas.

[Basillicum]

GralphidB wrote:

Ok, so here's some ideas:

1. The "planet" is really a moon, orbiting a gas giant with a highly eccentric orbit. In fall, it's far enough away from the sun that the sun isn't incredibly obvious (it's a pretty bright star, probably as bright as the full moon). The world is pretty dark 24 hours, but a reasonably thick atmosphere and tidal heating keeps it from getting TOO cold. In the summer, you swing close to the star, which provides additional heating and light.

2. Same as before, but you orbit a small red dwarf star rather than a gas giant. This helps fix the light problem, while still getting everything else.

3. If you want to be really crazy: A triple system of star, small star, black hole. The planet orbits close to the small star, which orbits in a figure eight back and forth between star and black hole/neutron star. Around black hole its "winter" and around star its high summer, and in between is fall. A deity level power keeps this stable (since it wouldn't be naturally). The people on the world wouldn't necessarily know the black hole even exists, since it's black.

Option 2 and 3 are definitely the most attractive.

I think the triple system gets me closest to what I want, but I'm not sure I understand the concept of a figure eight orbit in a system like that. Does it still count as a triple system when the small star has its own orbit without being paired with either the star or the black hole? (note: I've only just now started to try to read up on this stuff)

Making the habitable planet the moon of a red dwarf would obviously make everything easier while still satisfying my wishes, but it's much more fun to complicate things!

[Basillicum]

Chemlak wrote:

I'm currently wondering if a highly elliptical very small second star (so, a binary system) with perihelion, say, .75 AU, inclined to 10-15 degrees from the ecliptic, aphelion around 4-5 AU. If it's dim enough it won't be too bright an object in the sky, and orbital crossover risk will be negligible to nonexistent.

Just tossing out ideas.

AU is to measure distance from the host star, correct? So the "High Summer" season in my world would be around the second star's aphelion, assuming this is when the second star is closest to the planet?

[BiosTheo]

You know all this talk of planetary orbits maintained by a deity just gave me a terrible campaign idea: Rovagug wants to trick the party into stopping the deities influence and thereby destroy the planet. I need to go write this down.

[GralphidB]

Basillicum wrote:

Option 2 and 3 are definitely the most attractive.

I think the triple system gets me closest to what I want, but I'm not sure I understand the concept of a figure eight orbit in a system like that. Does it still count as a triple system when the small star has its own orbit without being paired with either the star or the black hole? (note: I've only just now started to try to read up on this stuff)

Making the habitable planet the moon of a red dwarf would obviously make everything easier while still satisfying my wishes, but it's much more fun to complicate things!

Basically, the stars orbit around each other in circles (ellipses actually, but never mind that). If you take a camera that is looking at the system and rotate it at exactly the same rate that the stars are orbiting, they appear motionless. In this "frame of reference" the planet then rotates in a figure eight, going back and forth between the two stars. As I mentioned, this is technically possible but unstable: even a slight perturbation will cause the planet's motion to become chaotic.

Basillicum wrote:

AU is to measure distance from the host star, correct? So the "High Summer" season in my world would be around the second star's aphelion, assuming this is when the second star is closest to the planet?

AU is just a unit of distance, defined to be equal to the average distance between the Earth and the Sun. Chemlak's idea is interesting, however (assuming the main star is roughly the mass of the sun) with those distances, you'd have an orbit of roughly 4 years, so you'd have "high summer" once per 4 years, rather than once per nine months. However, doing something like would otherwise mostly grant what you want.

The other problem is having a second star (even a low mass one) that close in your planet would turn your planet's motion into a restricted three body problem, which is inherently chaotic (ie, your planet will have it's orbital distance change rapidly with time, making life as we know it impossible). The problem is a three body system has exactly two stable orbital configurations and one unstable closed orbit, and everything else is massively chaotic.