Multiple moons and tidal forces

[thullgrim]

can anyone point towards a source that would describe the effects of multiple moons on tidal forces? I am beginning work on a homebrew, and am trying to keep things as realistic as possible. I understand that the orbital distances will probably be a factor in determining just how much effect a given moon would have on the tides. The world I am envisioning has 5 moons 2 sets of two grouped rather closely together and the 5th moon stands alone. Any help would be great.

Thanks

 

[MerakSpielman]

I can tell you straight off that developing a tidal chart would be hellish, especially if all the moons travel at variable speeds and are different masses. When they are all on one side of the planet, the tides will be extreme. When they are all equally distributed, the tidal changes will be minor.

 

[Drawmack]

With four moons very close to one another the tides are going to be rather viscious unless those moons are very small.

What you might want to consider is having the five moons work like this. Two groups of two that orbit in opposite directions. Then have the lone moon bee much larger and move such that it is always directly across from the other moons when the two sets are on top of each other. This would keep your tides pretty much normal except you'd have 4 per day instead of two. Also having them orbit this way would make your moon cycles very strange and probably lead the people of the world to do astrology based on the moons more so then the stars and each moon would likely have a god associated with it.

Here are some good resources for this type of thing:
http://www.salem.mass.edu/~lhanson/gls214/gls214_tides.html
http://oceanlink.island.net/oinfo/tides/tides.html
http://teach.fhu.edu/technology/EDU506/WebQuests/tides/tides.html
http://users.efni.com/~brentt/tourist/ss04.htm

Hope that helps.

 

[the Jester]

I think it would really depend on their relative masses, orbital distances (and shapes), etc. You're looking to make a lot of work for yourself- I wouldn't bother too much, frankly, but that's me.

 

[Vaxalon]

You want realism?

The tides are easy. There are none.

Why?

Because in order for a planet to have multiple moons in stable orbits, they must be very small in relation to the planet. This means that the major tidal influence is the sun, so the high tides come at noon and midnight.

Except that a world without a large moon, within the "life zone" of a star that is old enough to have life, is going to be tide-locked to that star. That means that one side will ALWAYS be noon, and the other will ALWAYS be midnight.

So no tides. No oceans, either. Just a narrow band of habitable land in the "dusk zone" between the nearside desert and the cold farside wastes.

Aren't you glad that you slaved yourself to Real World Physics?

Now if you'd like to break free of those shackles, we can talk about INTERESTING tides.

Tides that are ruled by magic.

Tides that are determined by their own rules.

Tides that are influenced by divine and/or infernal forces.

 

[Drawmack]

Because in order for a planet to have multiple moons in stable orbits, they must be very small in relation to the planet. This means that the major tidal influence is the sun, so the high tides come at noon and midnight.

Why would the moons have to be very small in relation to the planet, I don't understand this. Probably has something to do with gravitational forces, would be nice to have it explained though.

Except that a world without a large moon, within the "life zone" of a star that is old enough to have life, is going to be tide-locked to that star. That means that one side will ALWAYS be noon, and the other will ALWAYS be midnight.

Tide-locked? As in the world does not spin on it's axis, or it spins exactly as it rotates there by creating the illusion that it doesn't spin. Like our moon's light side and dark side. Again it would be nice to have this explained.

So no tides. No oceans, either. Just a narrow band of habitable land in the "dusk zone" between the nearside desert and the cold farside wastes.

Once the above is explained this will make sense.

 

[Balgus]

not only would todal forces be extreme, but also other geologic activity. Earthquakes, Volcanic eruptions, hurricanes and tornadoes, all would be 100X worse than what we are experiencing now.

Just go back like a billion years (research) and that would be the environment you want. lots of geologic activity- and fierce ones at that...

 

[BiggusGeekus@Work]

I tried to do this for my three moon world and quit. It is indeed a hellish process. My "solution" was to make one moon very low-mass and another far away. So only one moon "counts" toward the tides but I can feel free to tweak it if I need to, due to the minor influence of the other two moons.

 

[MerakSpielman]

This IS a magical world, though, right? Who says the moons have to be made of rock? say, 4 moons made out of Earth, Air, Fire, and Water? Only the Earth and Water ones would have enough mass to cause tides. The way to travel to the elemental plains could be to fly into a moon!

 

[Aeolius]

Here's a website where someone attempted to determine the tides of Oerth, which has two moons:

http://www.nirgal.com/games/rpg/greyhawk/tides_math