# Three moon planet



## Neybug (Jun 6, 2013)

I am writing a sci fi/fantasy novel with a planet that has three moons. I have reached the point in the book where I need to accurately describe their effect on the tides and want to make sure I have this right. It is difficult to compare them to large gas planets with multiple moons because of the difference in mass. I have worked out that the moons cause a balance in axis tilt and that the give and take gravity between the planet and moons causes the moons to have atmospheres and are farmable. This is a watery planet with large oceans. Would cities even be able to be built near the shore? Do I need to incorporate massive sea walls? Also, any ideas on what ship commerce would be like?


----------



## Penpilot (Jun 7, 2013)

Honestly, how the moons affect the planet is completely up to you. I'm no astronomer but, if the three moons are in a very high orbit, their effects may not be that great when compared to one moon orbiting very close. If the moons happen to be in a geosynchronous orbit they might not have any noticeable affect at all. IMHO just think of what effects make the coolest story and used that.


----------



## PaulineMRoss (Jun 7, 2013)

In Chris Wooding's Braided Path trilogy, the world had three moons. When they were in conjunction, there was a sudden mega storm, lots of wind and rain, bad enough that the characters had to take shelter, so it made a useful plot device. Afterwards there was a period when sparkly stuff fell, a sort of twinkly rain (he describes it much better - it's very cool in the book!).

Basically, it's fantasy. If your moons are magically enhanced, you can let them have whatever effect you like


----------



## Neybug (Jun 7, 2013)

Thank you! So far I have incorporated very high tides when the two larger moons are near each other. I think adding a corresponding storm in certain regions would really add to the effects of the moons. I have to stay a little true to the science since this is sci fi/fantasy. There is a supernatural element to the story, but the laws of physics apply in something like this. I've considered placing this planet in a separate universe since my races float, rather than walk and I am having a hard time supporting this element with acceptable levels of gravity on a rocky planet!


----------



## Neybug (Jun 7, 2013)

Thanks for the tip on geosynchronous orbit! I have the moons orbiting at different speeds based on their mass. The larger moons do effect the tides for sure, but I think the smaller one can orbit fast enough and has small enough mass that does not effect the tides or weather.


----------



## Awakened Victim (Jun 7, 2013)

Another thing to think about:

I saw on a science show the other day that since Mars has multiple moons, and they vary in distance from the planet, you could see a particular moon going across the night sky two or three times a night, while others may only go across once, or not even get all the way across by the time the sun came up.


----------



## Addison (Jun 7, 2013)

Is the facts of how the moons affect the planet relevant? Necessary? If not then don't bother with them. 

If they do then I suggest taking a look at the moons Europa, Io and Titan around Jupiter. Obviously we don't know how Jupiter is affected by the moons but we do know how the moons interact with each other (which may help you)

Io-the closest moon, Volcanic, hot, zero potential for life. It's constant heat and volcanic activity is caused by tidal heating.This is caused by both Europa and Jupiter. When Io's is smack between Jupiter and Io their gravitational pulls pull the planet in two directions. Then he's sling-shotted out of that trap and around Jupiter (eliptical orbit), but is still heated by Jupiter's pull. For every two orbits Io does around Jupiter, Europa does one. 

Europa - Larger than Io with a greater possibility for life. Under its thick icy crust is an ocean. Due to the millions of cracks and crevices and salty deposits on the surface it's believed that Europa has some sort of internal energy which causes the ice to break and move. Possibly hot vents at the center. Europa receives its energy from the gravitational pull of Jupiter and possibly occasionally Io. 

There's also Titan but other than the facts that it has oceans of methane, a thicker atmosphere than the other moons and a land with rivers, hills, dirt and such, I don't remember how it's affected by the other planets or moons. 

So maybe the geology of the moons can help with some explanations. 

Just a thought.


----------



## Neybug (Jun 7, 2013)

Yes! My small moon crosses the sky twice in a night, while the larger moons cross just once.


----------



## Neybug (Jun 7, 2013)

This is funny you would bring it up because I am kind of obsessed with the moons of Jupiter. Titan is especially fascinating with its nitrogen/methane atmosphere and earth like processes (methane rain, erosion, possible seasons). The Cassini mission results gave me the idea to put atmospheres and farming facilities on my moons, although these atmospheres are partially manipulated by the races on my planet.


----------



## Creed (Jun 11, 2013)

The use of moons to add a fantasy aspect is always a fun idea!*
My current WIP has a planet with five moons (but three are lesser) so there are some very important things to consider. You specifically asked about the sea and such.*
For me, travelling by ocean is a dangerous (and thus expensive) choice. I posted a thread about how to make an effective harbour in my world, which is something I had fun with and intend to explore in one of my character's POV. Can people live by the sea? Yes, but with innovation. Buffer areas might be a good idea for anywhere that harbours are unnecessary. Sea walls came up in the thread, too. I focus a lot on the theology of my moons, but there are certainly some technical aspects that need to be considered.*


> I've considered placing this planet in a separate universe since my races float, rather than walk…


But if your people float, then what's the point of harbours? Or even boats? Do they live in floating cities on the surface of the ocean? If so, then you'll need to account for the violence of the seas- like the storms Kaiku and the others (Braided Path) had to weather (no pun intended!) and the tides.*


----------



## Neybug (Jun 13, 2013)

Good post! I did incorporate sea walls in my one city and reinforced docks that stand above the tide zone. One race has submarines, the other two sail just above the waves. They do levitate, but the alien race has to learn it, while the native race have the ability from birth. They live on the land, but do have mountain cities where the city is built on shallow "levels" in the mountains. I tried to make this world a combination of conservation and high tech, so the science is advanced, but it has kept the environment in mind. I glean tech ideas from TED talks and random searches on the Internet but then I have to ask myself "will it work on this planet and how does it effect the environment?"
P.S. for posters and readers: this is my first novel. It is the first book in a trilogy with a possible prequel. I am writing it with my sister and we are on chapter six out of 11 or about 40,000 words in.


----------



## Neybug (Jun 13, 2013)

Oh and five moons would look amazing in a movie...even the small ones give some light at night. How bright are your nights? I've thought about incorporating specific "lunar" plant species...sort of like our Epiphyllum flowers (cacti) that bloom only at night. Perhaps evening gardens dedicated to these plants where the people have parties at night.


----------



## Creed (Jun 13, 2013)

I know! It would look so cool!*
I never really could imagine what it looked like until I played Oblivion and Skyrim, and Skyrim just made it look amazing.*
As for brightness, these moons are mostly tide-locked like ours is, but not in the same way. Of the five moons, two are major. These are Vaki (the largest) and Morin (next largest). Morin is out during the night (it's got religious significance- sort of like the reminder that even when it's darkest, there's a light (Morin in my language translates to "faith")). Vaki is usually out during the day, but every few years is tugged along by outside gravitational forces and crosses the night sky, too (in the period of about a month). So it's not too bright. I've been looking at the physical sides, but I'm most intrigued by the theological and philosophical effects that these moons have had on the people of Urd (the planet). I'll have to post a thread on it sometime, just to see what everyone thinks.*
But I do like the idea of a lunar flower- that sounds really cool!*
You said that your world's inhabitants farm on a moon, so I'm curious as to how your moons contribute to agriculture as it is. Are the lands dry and harsh, or wet and lush? I considered a sort of monsoon-like thing powered by the moons, but decided against it. Storms, however, are bigger for me.*
And what exactly is it that makes these natives float? I'm assuming some sort of magic or mind power. And based I that assumption, how do the others go about learning it? Is it induced by some chemical or treatment or something, or perhaps attained through… concentration or meditation?*
P.S. I think it's pretty cool that you're writing it with your sister! I tried making a trilogy with two friends, but after a month's worth of planning we all had different directions we wanted to go with the story.


----------



## SineNomine (Jun 14, 2013)

First of all, come on guys, Titan is a moon of Saturn, not Jupiter!  No more crazy talk!

As for the actual problem at hand, there are so many things to take into account if you want it to be accurate.  The easiest method is just ignore it as someone else said.  Leave out all the details, include seawalls if they are cool and leave them out if they aren't, and then just be a bit more vague when talking about the moons in any way that could be seen as scientific.  There is a LOT of room to handwave and the key is to not get caught half way between accurate physics and handwave.  People only need an explanation if an attempt at an explanation is given.

Orbital mechanics are so full of cool stuff its hard to compress down.  It depends on how large the moons are in relation to the planet, how large they are in relation to each other, to a small extent some absolute mass issues (Bodies need to have a certain mass before they pull themselves into spheres for example, and any body smaller than that limit is extremely lumpy), and then of course the distances between all the moons and the planet.

If you really care, there are a few things to note.  Phobos and Deimos, Mars's moons, orbit extremely fast.  Phobos has a period of 7 hours, Deimos 30 hours.  That's cool, but you should note that it's because they are TINY and extremely close. The bigger one is about 11km across on average.  And the further of the two orbits only 23,000km above mars, compared to the moon being around 380,000km from us.  Fast orbits needs moons to be dinky and close.

The most prevalent orbital mechanic you should care about is orbital resonance.  To put it simply, this is a simple ratio between, most commonly, the orbital period of the moons involved.  The biggest example is of course Jupiter's moons Ganymede, Europa, and Io.  They orbit Jupiter with a 1:2:4 ratio, meaning that for every 1 time Ganymede orbits jupiter, Europa has gone around 2 times, and Io has gone around 4 times.  Moons don't absolutely have to, but tend to either fall into orbital resonances or be ejected.  When you have multiple bodies orbiting, you always are dealing with constant pulls and tugs, so those pulls and tugs almost always result in the moon flying away, crashing into the planet, or lining up just right so that they reach equilibrium.  That's really easy to work into the story and has some cool implications for how time-keeping might occur.

...ok, there is too much to just cover in one single sitting, especially when it is easier to just make everything work sans-physics in fantasy.  So I'll just leave with this:  One of the coolest orbits that we know of is that of the Saturn moons Janus and Epimetheus.  They orbit at around the same distance from saturn, meaning they functionally share the same orbit path.  Usually that is completely unstable but in this case it reached stability by perpetually having one moon catching up to the other, then in the process slowing down and speeding up the other moon so that neither can overtake the other.  You can read up on it here.  Co-orbital configuration - Wikipedia, the free encyclopedia


----------



## Creed (Jun 15, 2013)

I thought Titan belonged to Saturn! In grade 9 we had to make a study of one of our exoplanets, and I chose Saturn.*
I haven't taken a physics class yet, like I had hoped to, but I've read about some things. One of the ideas I had and am implementing is the use of a moon's orbital eccentricity. I have a small moon, covered in carbon after millennia of volcanic action, and this moon gets sort-of flung out into space, and out of sight. But it does come back, and the people hold a great festival when the "black star" returns. It's cool because the moon is Neveth, or salvation, and it represents the corrupt soul leaving the Almighty's light and eventually finding absolution.
But yes, it is important to remember that science and imagination can be used in tandem without, you know, all the technical aspects being perfect. This is fantasy, after all. It doesn't have to be realistic at all, but giving it some grounds in history, science, or the realm of the possible is, in my opinion, most certainly a good thing.


----------



## Neybug (Jun 21, 2013)

SineNomine said:


> First of all, come on guys, Titan is a moon of Saturn, not Jupiter!  No more crazy talk!
> 
> *facepalm* thank you for pointing that out, will edit above post right now! Thank you for all the insights! I like the Janus and Epimetheus co-orbit idea.


----------



## Neybug (Jun 21, 2013)

"And what exactly is it that makes these natives float? I'm assuming some sort of magic or mind power. And based I that assumption, how do the others go about learning it? Is it induced by some chemical or treatment or something, or perhaps attained through… concentration or meditation?"

The gravity is not so low that everything is just floating above the surface but rather the natives have an innate ability to do this from a young age, while the alien "Domans" now called "Invado" have to train their minds to achieve levitation. Their old planet had similar gravity to Earth. It is something of a meditation state, but it does become natural after training. The ability is related to the supernatural element that qualifies this story as fantasy along with sci fi.


----------



## Sheilawisz (Jun 26, 2013)

I love the idea of a planet with multiple moons, and I sometimes wish that we had more than one moon nearby Earth. Maybe we could have two moons or a single, larger one... just imagine what the night sky would look like!

There is a planet with three moons in one of my Fantasy stories, and these are differently colored moons: Violet, white and blue. They really have an important effect on the axis and the weather of the planet, but because they are smaller than Earth's moon, they cannot cause a very powerful effect.

The effects that your three moons would have on your planet would depend on the size of those moons (or more precisely, their mass and gravity) and how far they are from the planet. Earth is sometimes said to be a _double planet_ because our moon is very large and critically important, while the moons of Mars are so small that they do not really affect that planet.

Also, you may want to consider that the multiple moons could have a great influence on your planet's culture, religions, seasons, harvest cycle and calendar systems...


----------



## Asterisk (Aug 5, 2013)

My world has three moons as well, so this thread was really thought provoking. I haven't thought about the way the moons affect tides yet or how/when they travel the sky. I have a lot to think about now!


----------

