World Building 101: Do You Really Want That Second Moon?

I love writing both fantasy and science fiction, but I’ve learned to be cautious about my planetology in both genres, and I think more writers should as well.

Red Moon and Black Mountain by Joy Chant was one of my favorite fantasy novels when I was a girl, in part because the world of Vandarei she created was so incredibly vivid and real. This was the first book that made me realize that other worlds might have more than one moon. And her red moon wasn’t just up there in the sky for decoration. When it was full and rose on one particular night in the year, the powers of her evil villain were at their strongest.

But I would venture to guess (my apologies to Ms. Chant if I’m wrong) that she probably didn’t chart the orbits of her red moon and her silver one too carefully, or keep track of when they should be rising and setting. Magic is a handy explanation for why one moon orbiting the same planet and same star is silver and the other moon is blood red. You can be a little more relaxed about orbits and your planetology in fantasy, but in science fiction, your fans may expect your moons to behave like real satellites, with real, predictable orbits and plausible colors.

If you write science fiction and decide to give your world extra moons, at the very least you should be aware of the impact of those moons in terms of their gravitational pull on large bodies of water. If your planet has seas and all three of your moons are in alignment, your characters are going to have to deal with some epic tides. But I’ve read dozens of science fiction novels in which the moons rise whenever their authors needs them to, and their gravitational pull appears to have no apparent impact on the planet. That disregard for the laws of physics erodes my belief in an author’s story.

If you set your book on a planet with an irregular orbit, that could explain spectacular weather anomalies that play havoc with the climate of your world. Winter is coming, but if your characters aren’t sophisticated astronomers, they might not be able to predict when that winter is going start or how long it might last. Patricia McKillip took this idea several steps further and hypothesized that members of a primitive culture might base some of its religious beliefs around a brilliant flash of light they saw on their moon each year. But that flash actually came from a supply ship landing on a satellite, and she wrote a thought-provoking novel about that clash of cultures in her novel Moon Flash.

Extra moons and irregular orbits can instantly make your world seem more exotic and foreign, but with extra moons comes great responsibility. You may lose some of your true science fiction fans if your moons and planets don’t obey the rules of science.

Polly Holyoke is June's first Affiliate Blogger. To find out more about our guest author positions here at the League, click here.

Polly Holyoke graduated from Middlebury College and earned her teaching certificate from theUniversity of Colorado. She loved working as a middle school social studies teacher and has been writing stories since she was in fifth grade. When she isn’t tapping away on her computer, Polly enjoys reading, camping, skiing, scuba diving and hiking in the desert. She lives with three rescue dogs, two spoiled cats and a very nice husband who tolerates piles of books all over their house.

The Neptune Project

by Polly Holyoke

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The Neptune Project is set in a future where the seas are rising and wars and famines wrack the surface world. Nere Hanson and her teen companions are shocked to learn that they have been genetically altered by their desperate parents to live in the sea. Protected by her loyal dolphins, shy Nere leads the rest on a perilous journey to her father’s new colony. Fighting off government divers, sharks and giant squid, can Nere and her companions learn to trust each other before their dangerous new world destroys them?