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MartinaMay
03-09-2013, 07:14 PM
I'm writing a YA book on a planet far from Earth.

I initially had 2 moons in my sky; in differing orbits, differing sizes/colors. They will wax and wane. I don't want my moons to play a huge role in my plot.

Sadly enough, they're suppose to look nice as they move through the sky, light up the night somewhat, etc. I don't want to spend much of my story focusing on them beyond that.

However, I also don't want to pull a reader out of my story by using details that wouldn't make scientific sense, so I have to have some basis for believability.

So, my questions are:
- Can 2 moons theoretically work on another planet that is Earthlike and if so, how? I've looked a little into the 2 moons of Saturn and it's believed they orbit in a horseshoe shape. Could I use this somehow and if so, what would it look like from the ground?
- Or, should I only have one moon so I can have similar gravity to Earth and make it easier on myself? The point of the story was to have the kids living on a planet similar to Earth, yet foreign at the same time.

I'm open to suggestions, ideas. Thanks in advance.

Bufty
03-09-2013, 07:24 PM
If it's fantasy I wouldn't worry too much about it, especially if they are there for scenic reasons only and don't play a part in the story. One could be farther away than the other. Can you see them both at the same time?

The views from the ground would be the same as the views you get of the moon here - assuming the planet's orbiting the/a sun.

If it's science fiction you may want to consider tidal and weather complications if these affect areas of the story.

King Neptune
03-09-2013, 07:35 PM
So, my questions are:
- Can 2 moons theoretically work on another planet that is Earthlike and if so, how? I've looked a little into the 2 moons of Saturn and it's believed they orbit in a horseshoe shape. Could I use this somehow and if so, what would it look like from the ground?
- Or, should I only have one moon so I can have similar gravity to Earth and make it easier on myself? The point of the story was to have the kids living on a planet similar to Earth, yet foreign at the same time.

I'm open to suggestions, ideas. Thanks in advance.

While two moons might be workable for an Earthlike planet. There might be problems, because the Earth's Moon is partly responsible for the Earth being habitable by beaties like us. The Moon has pulled away the thick atmosphere, much like Venus', that Earth had in earlier eras. It is possible that two moons could do the same, but it would be more complicated. A large moon in a fairly close orbit and a small moon in a distant orbit would do the same to the atmosphere, and they might be pleasant to look at. Two moons in similar orbits could create problems, but they could also clear the atmosphere.

One way around would be that there wqas one large moon that was broken in a collision.

MartinaMay
03-09-2013, 07:48 PM
Thank you both!

A large moon in a fairly close orbit and a small moon in a distant orbit would do the same to the atmosphere, and they might be pleasant to look at. Two moons in similar orbits could create problems, but they could also clear the atmosphere.

This is what I was thinking about exactly. I had a larger moon and a smaller moon in differing orbits then went back and changed it to just one moon. However, I think that two moons would lend to the otherwordly experience in my book. Your suggestion gives me hope I can make it work.

Now, if the big moon was closer, would it be in a faster or slower orbit than the smaller moon? Also, how could they theoretically wax and wane in a way I could describe simply, perhaps when two of the kids looked up at varying times?

King Neptune
03-09-2013, 10:44 PM
Thank you both!

A large moon in a fairly close orbit and a small moon in a distant orbit would do the same to the atmosphere, and they might be pleasant to look at. Two moons in similar orbits could create problems, but they could also clear the atmosphere.

This is what I was thinking about exactly. I had a larger moon and a smaller moon in differing orbits then went back and changed it to just one moon. However, I think that two moons would lend to the otherwordly experience in my book. Your suggestion gives me hope I can make it work.

Now, if the big moon was closer, would it be in a faster or slower orbit than the smaller moon? Also, how could they theoretically wax and wane in a way I could describe simply, perhaps when two of the kids looked up at varying times?

If the smaller moon were farther from the planet, then it would move slower than if it were closer. So the larger moon would have a shorter period. The period of an orbitting is proportionate to its mass; the greater the mass the faster it has to move to avoid being pulled into the body areound which it orbits. If the Earth were tolose mass and retain its orbital speed, then it would move closer to the Sun.

Here's a page that kind of explains it.
http://www.astronomynotes.com/gravappl/s8.htm

As for waxing and waning, that is a matter of the angle between the star and the moon. Both moons would wax and wane much as the Moon does.

jaksen
03-10-2013, 01:34 AM
This has nothing to do with your two-moon idea, which I think is an excellent thing to include in a novel, or story, but Saturn has over 60 moons.

Just thought I'd add that in ...

blacbird
03-10-2013, 01:34 AM
I've looked a little into the 2 moons of Saturn and it's believed they orbit in a horseshoe shape.

Google is your friend here. It sounds like you really need to do some astronomical research. For starters, Saturn has 62 known natural satellites, most of them small, but one (Titan) larger than our own, and several others of significant diameter.

http://en.wikipedia.org/wiki/Moons_of_Saturn

If you don't want to take that trouble (and it really isn't very much trouble), AND you don't want this to be a big deal for your story, don't make it a big deal.

caw

StormChord
03-11-2013, 04:26 PM
Earth's moon is unusually large in comparison to Earth; we're more of a binary planetary system than anything else. Two smaller moons is actually more normal. Consider Mars, which has Phobos and Deimos.
If you want a world with two moons, you can have a world with two moons. Especially if they aren't a big deal. Nobody will object.

MartinaMay
03-11-2013, 05:13 PM
Thank you everyone for your thoughtful replies. I'm off to google (yahoo wasn't much help).

spice chai
03-12-2013, 07:13 AM
Keep researching, but to answer your questions - the lower the orbit, the faster it moves. And any object rotating around a planet is going to wax and wane, which is simply the fact that the sun can only light up the side of the moon that faces it. The other side of any body is going to be dark.