Creating a World - Need to Determine Seasons and Years (Page 1 of 2)

You've got an interesting physics problem.  Interesting in Physics means "damned hard, maybe insoluble with present math tools, maybe chaotic and thus truly insoluble (but look up 'strange attractors' online)".

Are the suns symmetrical?  If so, they revolve together about a point nearly centered between them.  If one is more massive,  the center of revolution will be nearer one than the other, maybe even within the larger one's outer corona.  Over astronomical ages, they will fall towards each other due to energy loss to gravity waves (General Relativity).  In some cases, long geological ages may approach short astronomical ages.  Whether this has affected biological evolution is a call for you to make.

The deeper the planet is within one sun's gravity well, the faster it must be moving to  avoid being pulled into that sun.

I could write between one and five thousand words on this, and never even get near writing solutions.  And since I've never studied orbital mechanics, it would take me a day or to a week just to get the simultaneous differential equations right, and days to weeks to find approaches to the solution.  I'll write the words if you like, but setting me on the math task would be either folly or desperation, and probably Sisyphusian (and cruel).

Isaac Asimov wrote a famous story, Nightfall, a generation or so ago.  It was before knowledge of mathematical chaos made it out of research papers and hand-waves a lot away, but you might get some sense of the problems from it.

Thanks for the site suggestion, B Douglas Slack! I missed your response, when I responded to njc.  I definitely have a lot to figure out, so if there is a way that site can help me come up with any type of baseline, I'll take all the help I can get!

Though theoretically possible, such an orbit is generally considered unstable -- from my research. My question thus becomes: Why would you want to create such a system which would require such a technical explanation for the reader. You could simply say it orbited binary stars without getting into the minutia of orbital detail which most readers could live without. If you make a generalization of the system, then the reader can visualize whatever details they need to accept your version of days and nights as described within the story. But it's your story, so do whatever makes you happy. Take care. Vern

"Three-body configurations" per se is not the same as a "figure eight" orbit. Yes, there is a specific circumstance where it might be stable but would it remain stable enough to support intelligent life over a long period? And since it is such a narrow range of possibility, why try to pass it off to the reader when it is unnecessary to build an alien world which would be credible. Trying to explain the technicality as presented in this post would appear as an info dump for the casual reader imho. That is my only issue. But as stated in my initial response, it is the authors choice to do as they please. Take care. Vern

You've got what njc calls an impossible situation. You'll need to pull out "magic". And by magic I mean either actual magic or sci-fi-magic such as a self-propelled planet. Here's why...

First of all, understand that Earth's orbit is not just because we're spinning around a stellar body, but because the sun is so heavy, it can yank the entire planet around (and several others) like we're a bunch of pebbles

Our sun (and ours is rather tiny as far as suns go) will crush entire planets to dust if they get into the wrong place. And it would easily eat them all if they slowed down too much and "fell".

Your biggest challenge lies here:

Where the little sun is attempting to yank your planet out of the grasp of the bigger sun. Your planet cannot survive two suns acting in different directions. It will become an asteroid belt. Each sun will claim a portion of it.

(Actually, the smaller sun probably won't be able to beat the larger sun unless the planet is moving too quickly for the larger sun to hold it (in which case the smaller sun won't be able to hold it either, and your planet will go spinning into deep space. Wheee!))

There are more issues than that, but I picked the largest. Now I wish to turn the question around and ask what the goal is of this orbit. I ask this, so I can suggest something that may accomplish this goal rather than having to use magic

I've basically ignored these problems with my stories set in a binary star system. I do have a figure-eight orbit, making one sun dominant at a time to reduce the difficulties. I talk about two sunrises and sunsets, but that's about the only effect. Of course, my world is a witch world. Although no explanation is given, the normal laws of physics don't apply, driving the humans from Earth a little dingy accordingly. I even suggested at one point (but cut it out for possible future use) that the inhabitants on the planet have a cosmology that is more consistent with Norse mythology than with scientific astronomy--and that they're both right.

The advantage of writing fantasy is you don't have to worry about what certain environmental conditions do--what winters that last several years would do to agriculture, for example. You just assert it and use it for an extended metaphor.

I'm going to check out that website, Bill, but I'm not going to even try to apply the three-body problem to it. Although I might get Dr. Diane Witherspoon to tackle it, she's still trying to figure out subspace mechanics and how mirrors eliminate the issue of non-simultaneity.

Yes, being able to turn one sun "off" at a time vastly reduces your headaches, and your story has sufficient "magic" / "science magic" to support it.

You still have a minor issue that two suns will want to orbit themselves (If they were stationary with respect to each other, they'd join up, and who needs that headache?). As a result the planet would have to travel faster on some parts of its orbit -- to stay ahead of the creeping sun. In effect your planet's orbit itself would have to be orbitting to stay out of the path of the sun. Now, the planet moving its entire orbit is possible if you introduce mass that will upset the balance. But of course, the question becomes how is that mass moving around to move the orbit where it needs to be.

Fun stuff!

Thank you, njc. This was something new for me to consider.  I am researching Lagrange Points now.

I have seen some responses that I should just make this vague and no one will care how accurate this is, or that I should just rely on magic to explain what physics/astrophysics cannot.  I am not intending to give a physics lesson in my book.  I would like to have all the physics worked out though, and include that in an index or reference at the beginning or end of the book.  This may become a series, and I intend to fully build this world and it's place in the universe.  I know that means a lot more work, but I think it will be worth it in the end, and it will make the world and the story be that much more rich and full.

I'm still reading through the replies, but I love that others are working through this struggle too, because it let's me know I'm not alone in having this type of struggle in the writing process. I'm also glad that this is proving to be a helpful thread for others too. Let's keep the discussion going!

My thought is that when the planet (Omphalia) goes around the bigger sun, it will pick up speed, that slingshots the planet around the sun and towards the smaller sun.  While it is going around that sun, it does need an outer force to pull it back towards the bigger sun.  Maybe a black hole that will start to pull it away, but then the bigger sun grabs hold and pulls it back around.  Either something like that, or in between the 2 suns is a wormhole. In that scenario, the 2 suns aren't near either other at all, but in different places in the cosmos. The worm hole causes the planet to enter and exit each sun's rotation as it hits that wormhole, as it comes around each sun. The only problem there, is that you wouldn't see 2 suns, unless the other sun is one it doesn't rotate around, but is close enough to see, on one of the sides of the cosmos, rotating around 1 of the suns. 

Still pondering.  I'll get there eventually.

Kdot hit the orbital mechanics question, though I suspect it's even a bit more interesting than that.  (Ooh!  It is!  Look up Lissajous Orbit and Halo Orbit on Wikipedia.  If you can use an orbit around a Lagrange point, they might work for you.  Oh,yes: Look up Lagrangian Point, too.)  But first I'd like to talk about your planet's thermal equilibrium.  I'm going to belabor some basic points so you can follow the question a bit more deeply.

Heat is transferred though 'empty' space by radiation--light, that is, and mostly infrared for a habitable planet.  When we on the surface face the sun (daytime) we soak up its heat.  When we face the deep dark of space (nighttime) we radiate heat out into that abysssal void.  The very delicate balance of heat absorbed and heat released creates the narrow band of temperature in which life is possible on most of our planet.  And they most important limits are the melting/freezing point of water and the temperatures at which proteins start to denature.  (Forget about silicon-based life.  Bonds between silicon atoms are too damn strong.  No adhesive will bond to silicone.  Not even silicone adhesive.)

The next thing to understand is the inverse-square law.  This follows from a simple geometric reality: The surface area of  sphere increases in proportion to the square of the sphere's radius.  If an energy source (like a sun) is radiating in all directions from the center of a hollow sphere, the total energy released to the sphere is the same no matter the size of the sphere.  But the energy that hits a patch of fixed area is a fraction of the total, and the fraction is the fixed area divided by the surface area of the sphere.  Since that area goes as the square of the sphere's radius, the energy available to that patch of fixed area goes as the inverse of the square of the radius.  And since the intensity of the energy flow (ie., the 'flux') is measured as energy per unit area, the intensity of radiation from your sun falls off as the square of the distance from the sun.

A nearly circular orbit will provide a nearly constant luminous intensity to the planet.  A highly elliptical orbit--or a figure-eight orbit--will create immense swings in heating and cooling.  Moreover, the planet's velocity will be highest at its nearest approach to the sun, where its gravitational potential energy is the lowest.  The sum of potential energy and kinetic energy of motion will be constant (neglecting relativistic and tidal losses over cosmic ages).  Note also that kinetic energy goes as the square of the speed.  In a noticeably elliptical orbit, your planet will race through a hot zone in one short season and mosey languidly through the heat-absorbing blackness of the void for the opposite, much longer season.  Life as we know it on earth is possible because earth's orbit is very nearly circular.

(A digression on ellipses: In an elliptical orbit, a light body travels in an ellipse around a much heavier body--and this isn't quite right; see below--with the heavy body at one of the two focus points of the ellipse.  The focus points lie on the major axis of the ellipse, and every point on the ellipse meets two constraints.  First, all points are in one plane.  Second, for each point the sum of the distances from the point to the two fociii is constant.)

Next question: When is a square foot not a square foot?  (If you are too square for feet, substitute 'meter'.  It's just a constant factor.)  Well ...

Imagine you are standing on earth, on a sunny day.  You hold in your hands a sheet of material one foot square, and you hold that sheet perpendicular to the sun's rays.  It receives one square foot of solar radiation.

Then you turn that sheet about an axis in the plane of the sheet, so that the plane of the sheet is no longer perpendicular to the sun's rays, but instead lies at an angle of 30 degrees from them.  Along the axis on which you rotated the sheet, the sheet still shadows the same distance it shadowed before, but along an axis perpendicular to the rotation axis (and perpendicular to the sun's rays) the shadow is shortened by half.  Your square foot of sheet is absorbing only half a square foot's worth of solar radiation because it is canted to 'look llike' half a square foot 'to the sun'.

You may be noticing a theme here Geometry Rules!  As always and ever it has.

Imagine now that you are standing on the earth's equator at high noon (local high noon) at one of the equinoxes.  You hold your foot-square sheet parallel to the surface of the earth (ie., perpendicular to a plumb line).  It receives one square foot worth of solar radiation.  (We'll neglect losses to the atmosphere to keep the problem simple.)  Imagine next that you are standing in Cairo, at local high noon, on the equinox.  Cairo is at thirty degrees north latitude, so your plumb line lies thirty degrees away from the line of solar radiation.  Your foot-square sheet now looks like root-three-over-two feet (about 0.87  square feet) to the sun.

Move to Montreal, at 45 degrees north latitude, local high noon on the equinox.  Your 'horizontal' square foot sheet presents only root-two-over-two square feet to the sun.  And when you set your square foot up in Helsinki at local high noon on the equinox at sixty degrees north latitude, you'll be presenting only half a square foot to the ever-generous sun and its radiation.

Belabor, belabor, belabor ...

Okay, we're getting to seasons and tilt of the planet's rotational axis.  I'm assuming that your planet will have at least some of that.  You could make it weird and have the axis in the plane of the orbit, but that means that during the 'year' there will be times when one hemisphere is in continual hot day and the other is in frigid, sky-void-cold night.  (Speaking of planetary rotation, will your planet have a magnetic field?  Very good for keeping particle radiation away from the surface.)

You're going to have to figure out how much energy is coming off each sun, and how that relates to stellar mass and age.  (See Stellar Evolution on Wikipedia.)  Small, even very small, changes will have major consequences over time.

Remember when you learned that the earth orbits the sun?  Well, that's a lie.  The earth orbits the center of mass of the solar system, and because Jupiter is so massive, it pulls that center of mass outside the sun's corona.  The other planets can increase or decrease this effect, depending on where they are relative to Jupiter.  This means that earth is sometimes closer to the sun than at other times, depending on the position of Jupiter, and that is one reason why we have long-term cycles in climate.  (Solar sunspot cycles are another reason.)

I found another planet generator. This seems a little easier to use, but it's for setting up 1 planet, rather than a whole solar system:
http://planetmaker.wthr.us/#

And another one. I find this one a little confusing:
http://www.buildyourownearth.com/byoe.h … 0&v=pm

A good outline of the components to creating a world, that doesn't have to do with the revolution around any sun(s) but more it's makeup and boundaries (scroll down. ignore that download button)
https://m.wikihow-fun.com/Make-Your-Own-Fantasy-World

This thread has some suggestions of tools to use for documenting the pieces of your world. I haven't tried them yet. Still reading through the thread:
https://worldbuilding.stackexchange.com … your-world

I have yet to find a world generator where I can outline what is land and what is water, etc. This is important, because of Omphalia's topography, which is somewhat unique. I'll figure it out one way or another, but I see that I have a lot more to outline. I think this will be important, not because I will dump it on the reader, but because I have to have to have all the aspects outlined, so that I abide by my own rules.

It looks like there are a few ways to manage the figure 8 revolution, while avoiding the issues of how the gravity of one sun would overrule the gravity of the other.  I can get creative and involve some pull from a black hole, play with magnetic fields, worm holes, or involve some sort of "magic".  The world I am creating is not so much one that involves magic, but what people on earth would consider magic. It's meant to be a more evolved existence, where Omphalians have evolved to learn how to affect the elements on their planet.  Land, fire, air, water. and other elements that they have and we don't have or ones we haven't full discovered yet.

Lots of work to go, but this thread has helped me start to sketch "how" I can get myself there.

A planet that "revolves" (moves in a circular trajectory) around two different suns in a "figure eight"? Forget about reality--you left that a long time ago. (As have all the other authors who postulate two suns per planet.) Just relax and enjoy the unique world you have created!