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A World of Two Moons

"I couldn't help but notice how stunning the sky was. Luna was full and its silver moonlight made for a bright night... It's neighbor Oceana was still hard to miss, casting a blue glow from off in the distance. That moon was only half full, but still magnificent even among the endless sea of dancing lights." - You Can Count on Me, Welcome to Wis' Apothecary

Tierre is the name of the world our story takes place in, and from the earliest drafts, I always wanted it to be a world with two moons. This isn't just very important for magic, but culturally too. The Kingdom of Aramore uses a lunar calendar, as do most of the civilizations on the planet. So I thought I'd dig into that a little this week, and share some of the science I learned when imagining this world of two moons.

Luna and Oceana

As you read in the excerpt above, Luna is much like our moon, thus the name. It's the larger of the two moons, and closer to the planet. It's also the most widely used moon for timekeeping purposes, because as you can probably imagine, trying to use two moons to tell time would involve half months and all sorts of complicated shenanigans. So thanks to Luna, Aramore's year is divided into twelve, 30ish-day months just like our year.

Oceana is a smaller, icy moon with a crust of frozen water. It's also much further away from the planet. My inspiration for this moon was Europa, one of Jupiter's nearly eighty moons. I haven't given much thought yet as to whether or not some early version of the telescope exists in my world, but regardless if this information is known or not, its name would have come from the bluish appearance of its surface. Because it's further away, it takes Oceana eight-times longer to orbit around the planet. So an Oceana month would be 240ish days.

As I mentioned, the two moons are very important to my world, as is the "celestial sphere" in general. One of the dominant religions worships the Astral Gods, and the phases of the moons impact certain spells, potions and magical power. And of course, one of the largest winter holidays, which is important to a story in volume two, is the lunar new year.

To be honest, there was no deep reason behind my world having two moons. I simply thought it would be cool, and its certainly been done before. But in a story all about magic, imagine the fun that can be had when I introduce an eclipse, double full moons or syzygy (when planets and other celestial bodies align)!

Imagining a World with Two Moons

It's a fantasy world, and I could simply just leave it at that. But to help better imagine this concept, I ended up doing a lot of reading online. After all, it's not like this idea is totally fantastical. Earth has only one moon, but Mars has two. And as I mentioned previously, Jupiter has 79 while Saturn has even more.

What If has a pretty good video which explores a couple different scenarios if Earth had two moons. And in 2019, after a city in China announced the possibility of creating an artificial moon, Business Insider explored a similar thought experiment. They both agree that if the second moon was about the same size as our moon, the resulting tides would be catastrophic on our coastal cities. And eventually, after millions of years, the moons would collide and well... it wouldn't be pretty.

But if the second moon wasn't as big, the affect on tides wouldn't be as drastic. Waves would be larger, but not destructively so. In a coastal city like Aramore, they would have built up accordingly. And if there are island cultures out there in my world that surf, this is very good news for them.

However the most useful article I found comes from the gaming website Sagaborn, in which a scientist does a Q&A with his friend who created some kind of fictional world with two moons for a tabletop roleplay game (perhaps Dungeons and Dragons). And generally speaking, I can't stress enough how useful DND world building forums have been throughout the entire process.

Anyway, this scientist points out "moons that are created around rocky worlds, naturally, normally all form in approximately the same orbital plane." He uses Mars, with both of its moons, and Pluto, with five moons, as examples. This means something called resonance should happen, where the moons orbit together along a consistent ratio. Remember when I said Oceana takes eight times as long to rotate as Luna? He would call this an orbital resonance ratio of 1:8.

On Mars, Phobos orbits the planet three times a day, "while the more distant Deimos" takes thirty hours. They have a resonance ratio of 1:4 and align every 31 hours. On Tierre, with its Earthlike months, the two moons would align about once an Oceana-month (240 days), or every eight Luna-months. And because Luna is bigger than Oceana, this means Oceana would seem to disappear about once a year.

As for actual eclipses, a solar eclipse happens when the Moon comes between the planet and the Sun, while a Lunar eclipse happens when the planet passes between the Sun and the Moon. On Earth, this happens 4-7 times a year, but whether or not you can see it depends on where you are on the planet and whether or not its a partial or total eclipse.

On Tierre, there would be more eclipses because there are more bodies in the sky, but eclipses that involve all three would be much more rare. You can count on this coming up in a story at some point.

The Possibilities are Endless!

To me, that's the best part of a fantasy world, and why I've always been drawn to magic. In a world with two moons, are there different breeds of werewolves? If Luna became a blood moon during a lunar eclipse, would it mix with Oceana and give the night sky a purple hue? What rituals need to be cast on nights like these, or what potion components need to be harvested or found?

The only limit is my imagination, and that's why writing is so much fun.

Do you have any thoughts on this concept? Any stories you'd like to see me explore? Let me know in the comments, and of course, look forward to my lunar new year story in the volume to come! As always, thanks for reading.

Until next time!

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