I am working on a book with the presence of multiple moons acting as a quasi-astrology based religion whereby the irregular phases of the moons and their relationships between one another allow for 'predictions' to be made about the future. I have thus far worked with a system of twelve moons (don't all have to appear in the nightsky at once, better the more irregular actually). I'd take fewer, if needed for simplicity, but I do want more than a couple to allow for more complex 'readings' of the night. The really important detail is I need a thirteenth/ or additional rogue moon to appear once every ~1,000 years for magic/plot reasons. The moon does not need to remain in the sky for more than a day.

My concern for now revolves around the plausibility of such a planet. I do not want readers to be thrown out of the book for physics which does not make sense. Apart from regular eclipses and the impact that the different moons would have on tides, is there anything else that I should be adding to my worldbuilding that would legitimise the existence of the planet?

Thanks so much for your time!

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    $\begingroup$ Welcome to worldbuilding. Please read our help center to understand the kind of questions we do answer and which we don't. Give us the specific of your worldbuilding problem, "I am looking for information" is too vague for us. $\endgroup$
    – L.Dutch
    Nov 5, 2023 at 3:46
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    $\begingroup$ I see that this question has been closed. I will spend some time trying to learn a bit more about the stack exchange requirements and then maybe try again via the Sand Box first. I think unfortunately I just don't understand enough about astrophysics to start with to be able to ask more specific questions. Thanks anyway! $\endgroup$ Nov 5, 2023 at 12:37
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    $\begingroup$ @ElsbethAnne My first question is whether or not you need a science-as-we-understand-it-today-perfect planet? Mars has multiple moons, and their size wouldn't cause chaotic tides. We're standing on a habitable planet. So a lot of this (for SE's and our sakes) boils down to, what is the real problem that you're trying to overcome? In a real sense, you might be trying to reinvent the wheel. And that assumes that you need a full-science answer at all. SciFi has been imagining multiple big moons for a long time now. $\endgroup$
    – JBH
    Nov 5, 2023 at 16:31
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    $\begingroup$ @elemtilas Thank you both so much for the feedback, it has been really helpful. I have edited the post and have focused on one issue. Hopefully this is acceptable. $\endgroup$ Nov 6, 2023 at 22:37
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    $\begingroup$ @JBH I think perhaps I have been focusing too much on the science of it all and not accepting that readers will suspend disbelief in a fantasy world provided that there is some logic behind it. I have been trying to understand the exact science and equations behind it all which was incredibly overwhelming. Thanks for you input. $\endgroup$ Nov 6, 2023 at 22:40

1 Answer 1


This sounds really nifty. The planets in our solar system are arranged in a progressive distance from the sun - the outer ones' orbits are farther apart. The sun's gravitational pull on them is weaker because of the farther distance, so if they were the same distance apart their planet-to-planet grav. pull would have a greater tendency disrupt their orbits.

A couple of guys noticed that the orbits' radius, if plotted on a log scale, formed a nearly straight line. One of them was named Bode and it's called Bode's Law. The other guy's name is all but forgotten, for no particular reason.

Twelve moons, if they are not spaced out like that, will exhibit chaotic orbits. Jupiter has a bunch of moons, and a couple of them have orbits right close together. One of our spacecraft (not one that I worked on) discovered that when these two moons pass each other, they exchange orbits.

Another sweet thing: there's a lot of asteroids between Mars and Jupiter. Somebody had the idea that maybe a planet was there (the Mars-Jupe log distance is about 2x the rest, ie. there's an "empty orbit" there) and it got smashed for some reason. You need to read Terry Pratchett's /The Fifth Elephant/ sometime. The world is supported by 4 elephants walking around in a circle, but there were originally 5, one had a rough landing and his bones got shattered, which are the jewels to be found here and there in the earth.

Anyway, if an asteroid there were to have an orbital period of say 2X Jupiter's, it will pass closest to Jupe every other obit, right in the same place every time. The small tug it would get from Jupe would keep perturbing its orbit, so that eventually it would go zingin' off somewhere else. And what'dya know, the asteroid belt's chart has a gap at exactly that place, also 3X and 4X etc.

Now as to your astrology, I'm not into that but I can appreciate that people are. Your planet should have ancient literature that mentions it, as does ours. For instance, Genesis 1:14 (KJ): "And God said, Let there be lights in the firmament of the heaven to divide the day from the night; and let them be FOR SIGNS, and for seasons, and for days, and years." Also there's Revelation 15:1 - "And I saw another sign in heaven, great and marvellous..." I'd think you might have some astrologers, charlatans who claim to read the moons and give predictions, but then one real prophet who reads 'em correctly. Best of luck with it!


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