Multiple moon simulations? World-Building question

GeorgieB · Nov 30, 2009

Has anyone found a program where you could input say, 2 moons around a planet and play with their orbital period?

I need a planet with two moons with different orbital periods so that there are times when neither is visible to an observor, to times when one or the other is, etc.

If there's no program available, how would I go about writing a spreadsheet program to simulate it?

Thanks,

Port Iris · Nov 30, 2009

I'm not sure, but have you simply looked into finding a simulation of Mars' moons?

GeorgieB · Nov 30, 2009

Port Iris said:
I'm not sure, but have you simply looked into finding a simulation of Mars' moons?

That's not quite what I'm looking for. I would like to input data for two moons (orbital period, mass, etc.), then run the simulation to discover when one, both or neither of the moons would be visible to an observer on the planet.

The closest I've come so far is:

http://www.arachnoid.com/gravitation/

But that doesn't give times.

I suppose I could fake it for the sake of the story, but some sharp reader might spot any inaccuracy if I do so.

Juliette Wade · Nov 30, 2009

You know, a good place to find people who might help you with this is the readers forum for Analog magazine. There are tons of very serious scientists over there, many with an interest in just this sort of thing - as well as the kind of readers who might call you on inaccuracies in your story, lol. Anyway, excellent folk. I'd suggest you start a topic on their "The Hard Science" forum, here.

LOG · Nov 30, 2009

Let me ask this, does your story really require that you need to know the exact orbits and timing of it's satellites? Details help flesh out the world, but only to a point, they can quickly become cumbersome. There is also the danger of self-contradiction or being criticized for a highly un-feasible idea(*coughsparklyvampirescough*. Sometimes vagueness or simply not describing something is the best route to take.

bearilou · Dec 1, 2009

I'm with JJM on this. I just can't help but feel that if you leave it as vague as you can (simply be consistent within your world), the technical details will (and I'm so gonna be busted for this) honestly be worked out by the geeks who read your work and love it so much that they have to work out all the details themselves*. (Hardcore Trek fans, I'm looking at you) The rest of us, it doesn't really matter what the physics are behind it as long as you write well enough for us to suspend our disbelief.

Good luck!

*I live with one and he has a brother and I won't go into gory detail how many times I've sat in on debates and discussions at the kitchen table while they 'explain' the physics of some show they've watched or book they read that 'glosses' over these things to satisfy their own inner geeks.

GeorgieB · Dec 1, 2009

JJM and bearilou are both on the ball and correct. I'll include enough detail only to invoke the readers' sense that "this ain't Earth."

The only reason for asking was to make sure that my dual moon system didn't break any physical laws and "simply be consistent within [your] world." That's the crux of the matter.

My 'world' will have two moons, (cleverly named "White Moon" and "Red Moon"--at least for now). Conditions change when neither, one or both are visible. Setting the orbit of each determines those conditions and I wanted to experiment with orbits to get the time of the various overlaps.

Checking and searching the web, I found: www.gravitysimulator.com which is a downloadable program where you can vary the number of objects in orbit and play with parameters that determine their orbits. So, problem solved, except for the time I've been spending playing with the program.

Now, off to plot some more.

PeterL · Dec 1, 2009

The three body problem still hasn't been solved, unless someone did it recently. In theory describing the gravitational interactions of three bodies seems easy, but in the real world it is impossible. A vague guess would be safer than going into detail.

bearilou · Dec 1, 2009

GeorgieB said:
So, problem solved, except for the time I've been spending playing with the program.

YAY!

Pthom · Dec 1, 2009

If your planet has oceans, timing of tides would be really interesting with two moons as you propose. Sometimes, almost no change between high and low--and at other times: "Look out, Sarah, the tide's a'comin' in!"

Richard White · Dec 1, 2009

I built one of my fantasy worlds around two moons. One has a "monthly" schedule and one has a three-month long orbit, which makes identifying the "hunter's moon" (both moons full in the sky) and the "prey's moon" (neither moon visible in the sky) fun and after a while it became an important plot point.

LOG · Dec 1, 2009

I currently have two stories that involve satellites.
One is pretty similar to ours.
The other story has eight moons in orbit around an earth-like planet...>.>

jhmcmullen · Dec 3, 2009

I think Gillett's World-Building has a discussion of when to tell if a moon is visible (though it might just be a reference to go look at some astronomical ephemera).

Really, if the moons have different periods, they're at different distances. If you arbitrarily determine the periods and starting locations, you can figure out lunar-lunar eclipses and so on fairly easily. (So long as the moons aren't too close; see "Hill radius" for details, but if you do, you'll already be doing more world-building work than most writers do.) Solar-lunar eclipses take more work. (I am assuming the two moons are in the same plane. They might not be.)

Though I don't want to encourage anyone to get lost in world-building instead of writing the darn story, I find that certain things have to be in place, even in a fantasy world, or my fertile imagination produces self-contradictory works. I need a framework to imagine from.

Multiple moon simulations? World-Building question

GeorgieB

Almost a wannabe writer

Port Iris

GeorgieB

Almost a wannabe writer

Juliette Wade

Interprets for aliens

LOG

Lagrangian

bearilou

DenturePunk writer

GeorgieB

Almost a wannabe writer

PeterL

bearilou

DenturePunk writer

Pthom

Word butcher

Richard White

Stealthy Plot Bunny Peddler

LOG

Lagrangian

jhmcmullen