The Science of Aenya: Building a Better Fantasy World

Any fan of fantasy will tell you worldbuilding is a big part of why they love the genre. Ever since Tolkien hit the literary scene, authors of lesser imagination have been all too eager to cut and paste Middle Earth. Open any book from Robert Jordan’s The Wheel of Time to George RR Martin’s A Song of Ice and Fire to Kristin Cashore’s more recent Graceling series and what do you find? A map. Of a peninsula. Dotted with locations oh-oh-similar to Northern Europe. But here’s the thing, Tolkien’s brilliance was in doing what no other author had done before. The Lord of the Rings was unique, which is why it remains the standard-bearer of the genre to this day. If anything, newcomers to fantasy should be striving to create what others haven’t. But aside from Terry Pratchet’s Discworld series (where the world is imagined as a flat disc resting on four elephants who are themselves standing on a planet-sized turtle swimming through space) there’s really very little originality to be found.

When I was developing the Aenya Series (originally Enya) back in 2000, I wanted to bring something NEW to the table. Being of Greek heritage, Aenya is more inspired by Homer’s Iliad and Odyssey than Tolkien. I also decided that we’ve had enough of dwarves, elves, dragons, vampires, and evil wizards. Instead, Aenya features winged avians, aquatic merquid, and a primitive tribe of naked humans. And, while I wanted to emphasize character and story over setting, my worldbuilding was going to do what few others have done before, namely, Aenya was going to be a fantasy world based on science.

George RR Martin meticulously describes every horse in every hamlet in A Game of Thrones, except we, as readers, are left scratching our heads wondering about The Known World (really?). We don’t know if it’s a planet or a flat plane. If it orbits a star or has a moon similar to ours. And how, exactly, are those wacky seasons supposed to work? Winter is coming, sure, but why? Dragons the size of jumbo jets? What in the world do they eat? What about the square-cube law? Some of you out there might be thinking such questions are trivially pedantic, but if you have any interest in ANY of the sciences (biology, geology, meteorology, astronomy) these are questions begging for answers.

And that, dear readers, is what makes Aenya different! Plus, my map is a peninsula in reverse, with the dominant areas being land, which surrounds a central body of water, the One Sea.

But I’m no scientist, so I have had to rely on people a lot smarter than I am to bring my vision of a science-focused fantasy setting to life. Which brings me to a few weeks ago, when aerospace engineering student, Matthew Andrew, contacted me regarding the science of Aenya. Apparently, I had gotten quite a few things wrong! Thankfully, Matt helped me make sense of this fantastical world I’ve created. You can read our email exchange below:

Subject: On Aenya’s Cosmology
Message: Hello,

My name is Matthew, and I am an aerospace engineering student. I was looking through the cosmology section of Aenya and was rather impressed with the detail of the systems, but I have a few curious tidbits and inconsistencies I would like to have answered. Do understand that I am just a student and prone to mistakes/misunderstandings, but do not hesitate to ask for clarification if something is confusing.

The first thing is the apparent size of Aenya. In the picture with a given scale, it can be estimated that the diameter of Aenya is about 3500 km. However, at the very end, it is compared to Earth, with an apparent diameter 70% of Earth’s (about 9000 km). I was wondering if this is a mistake, or if the km mentioned in the first picture is using a different unit.

Secondly, I am also wondering about its rotation and orbit. As described, one hemisphere (presumed east) of Aenya always faces Infinity. Or Solos, it’s later contradicted. While Aenya should technically be tidally locked with Infinity, I understand there seems to be a permanent dark side of the Aenya, and the east’s light should be provided by the Greater Moon. If one side is perpetually against the sun while orbiting a gas giant, but Aenya is also tidally locked with Infinity such that there is some sort of rotation-orbit ratio (1:1. 2:3, 1:3, etc.). The only real definition for tidal-locking is that there is no change in the rotational period of an orbiting body, so Aenya’s orbit would have to match Infinity’s year (kind of like Venus). Accounting for libration and parallax would be fairly consistent with the description provided.

However, at this point, the other details, such as the seasons, orbital period of Aenya, and the exact orbit of Aenya. A cycle is ten days and the time it takes for Infinity to cross from north to south. Does that mean that Aenya is in a polar orbit? Is Aenya’s orbital period 20 days then? High Moon corresponds to Aenya’s periapsis, so does that mean that the seasonal cycle completes every twenty days (of course not accounting for Infinity’s position in its orbit).

As for now, that is all the questions that I have for right now. Do get back to me when you can.


Matthew Andrew

Hey Mathew, thanks for writing to me. Answering questions about Aenya always helps me think these things through. Just keep in mind, I am not a scientist. I studied a bit of astronomy in college, and have done some of my own research, but my degree/expertise is in literature/fiction. 

1)  Aenya is supposed to be roughly the size of Mars or 6000~7000 km. The ruler on the map measures the space between locations, but is inaccurate from a cosmic perspective, in the same way the Mercator projection map does not accurately depict the true sizes of Earth’s continents. 

2)  Aenya is not tidally locked to Solos (the parent star), only the gas giant (Infinity). Technically speaking, Aenya faces away from its sun when its orbit brings it opposite Infinity. Being tidally locked, the eastern hemisphere perpetually faces the same direction, with its rotational speed matching its orbit, like the Moon and the Earth.

3)  Seasons on Aenya have nothing to do with axial tilt. There is no summer, winter, etc., as we understand it. There is only high and low moon, which relates to the apogee and perigee of Infinity, and here, the climate is more greatly dependent on location than the time of year.

4)  So, to address your ten-day cycle query, allow me to first explain the big conceit of the Aenya series, which is my attempt to marry fantasy to Sci-Fi. Primarily, Aenya is a fantasy setting. However, because I have always been interested in astronomy, I could never help but ask, “Where, exactly, is Middle Earth in space? Is it even in space?” And “how do the decades-long seasons in A Game of Thrones work?” When I started writing about Aenya twenty years ago, I set out to create a fantasy world where such questions could be answered. I also wanted to do a little better in the realism department than so many soft Sci-Fi films and movies do today, like Prometheus and Lost in Space, which often makes little or no attempt at feasibility. 

What the characters know and experience sets the Aenya series in the fantasy genre; everything in the books is imagined through their eyes. Scientific knowledge is limited to what was known in ancient times (on Earth), which is why they wouldn’t know to call their world a moon and Infinity a planet. Time is measured based on what the people see, so a “passing” relates to the time it takes for the smaller moon to cross the larger, even though this isn’t always accurate.  

The ten-day cycle is meant to work in a similar way, marking the passage of time the way the American Indians used the lunar cycle. Aenya cannot have a polar orbit, because the climate, as described in the story, is similar to Earth’s in relation to latitude.

Let me just say, my only concern is in getting this right, so if you have any further questions, I am more than happy to address them. As for the ten-day cycle, how would you suggest correcting this? I need a way for my heroes to look up at the moon(s) and know that a *week* has gone by. Any help is appreciated. I’ll also give you a credit on the acknowledgments page of my upcoming book.   




Thank you for your reply. It is no worries at all about this. Before I was an aerospace engineer, I wanted to be an astronomer. Even so, I still immerse myself in a lot of cosmology and astronomy for that reason because I just find it so interesting. Furthermore, I have some more replies relating to your own.

1) Aenya as 7000 km makes sense. I measured diameter by hand, so I could always be off, but I was just wondering which picture was more accurate to its true size. Both were depicted as globes but depicted different sizes for Aenya. I don’t understand much of the mathematics behind maps, as I am not a cartographer.

2) As I understood it, Aenya was tidally locked to Infinity. I was wondering what its rotation was like in comparison to its orbit about Infinity. I (perhaps erroneously) understand that the western hemisphere is always pointing towards the sun. You, however, describe it to be a synchronous one (1:1). This confuses me a bit because you draw a comparison to the moon. The moon does not have a perpetual dark side, only a perpetual away side (in the sense that an observer on Earth can only ever see the same face of the moon). Likewise, this would also mean that Aenya would also not have a permanent dark side unless there is another variable (another orbiting body or otherwise) that I am not accounting for (or I once again misunderstand).

3) As I understand your statement, High Moon and Low Moon are not the periapsis and apoapsis of Aenya, but rather the perihelion and aphelion of Infinity about Solos, which in turn has influences on Aenya’s weather cycle. If that is what is being said, then great! I understand everything I wanted to know about the seasons. The wording on the cosmology page is a bit confusing, as it implies that the High Moon and Low Moon are dependent on Aenya’s orbit about Infinity, as opposed to Infinity’s around the sun.

4) I seem to have overcomplicated my own model because of the previous misunderstanding and as such need a bit more clarification for this. So, I will read a few excerpts from the cosmology page:

  1. A passing is roughly 80 minutes, the amount of time it takes for Eon to cross the face of Infinity. Since the larger moon is also moving, Eon can cross from left to right and back again from right to left.
  2. A cycle is ten days, and is similar to a lunar cycle on Earth. It is roughly the time it takes for Infinity to cross the sky from north to south. 

So, to start, a passing is measured as the time it takes for a moon of Infinity to transit across infinity. This usually takes an hour and twenty minutes. However, the next sentence confuses me. Because of another (larger) moon, Eon can make a retrograde motion, switching directions. Retrograde motion can’t be observed from a body that is consistently closer into an orbiting system. We never see Mercury or Venus do this with relation to the sun, they only ever go one way. However, we do see this with Mars and Jupiter, when we earthlings, who are on a faster orbit path, pass them in their slower and larger orbit paths. If Eon is closer in, we never see that described retrograde motion, and if Eon is always on the opposing side, then we never see it transit. So, my question is whether this retrograde motion is caused by Eon orbiting the larger moon which is orbiting Aenya (essentially a moon of a moon of a moon)?

The cycle, however, is what is confusing. I will wait for your next response before I begin to try and understand this concept as it relies on some previous questions (namely confirmation that I’ve got everything else right).


Matthew Andrew

OK, so the side of the moon we call the dark side is the one we cannot see. On Aenya, the “dark side” would be the side that perpetually faces Infinity. It’s basically the side that never faces the sun, although it does receive a considerable amount of reflective light so it isn’t entirely dark.

Sorry for the confusion, but high and low moon refers to how closely Aenya orbits the moon. I am not sure how greatly its distance from the sun would affect the climate. On Earth, we are closest to the sun during winter. Also keep in mind that, unlike our moon, which has minimal impact on the weather (aside from the tides) Infinity has a far great impact on Aenya. Think of the tidal forces impacting Jupiter’s and Saturn’s moons and you get the idea.

Eon is a very tiny moon of Infinity, not of Aenya. With all three bodies in motion, the retrograde aspect was meant to be apparent, not actual (the way you mentioned seeing planets appear to move backward when we are actually moving). This is what I was going for, anyway. But trying to visualize all this without some kind of model is very confusing. Maybe I can make an old-fashioned astrolabe. 

Sorry I couldn’t be more clear. As I said, I only dabble in astronomy. A long time ago, I actually reached out to Neil deGrasse Tyson for help, and I received a response from Alejandro Nunez, who works at the Hayden Planetarium. My main concern at the time was if you could have normal weather systems on such a world, because you cannot have a heroic story without the wind blowing in the hero’s hair (this is a scientific fact) and he said there was no problem. His biggest criticism was the “dark side” being dark, which I corrected. As for the rest, I didn’t really go into it.

The good news is, in the actual text of the novel, I left most of these details vague so that I could more easily update the information on my website. Again, any help with the clarifications is appreciated.    




I’m starting to understand a bit more. When you say dark side, you describe a synchronous rotation. The dark hemisphere is immersed in darkness (not accounting for reflection) due to it always facing away from the sun when coming in between Solos and Infinity. I understand that mechanism. The problem I mean to point out is that in an ordinary system (ordinary in the sense that there is resemblance/analog to Earth or Jupiter), the safe face won’t always eventually have a sunrise. For example, in the case where Solos, Infinity, and Aenya make a right triangle (or more or less a right triangle, assuming a 2D system, 3D gets sort of complicated), half of the dark hemisphere would be lit. As Aenya comes closer and closer to entering an eclipse, the dark side of Aenya would become more and more lit before being submerged into darkness by the eclipse. Meanwhile, the light side of Aenya would receive less and less sunlight throughout the rotation before also being submerged into darkness, but less so from the eclipse and more from facing away from the sun. I’ve attached a small illustration to help with the visualization of what I am trying to get across. 

Blue sphere is Infinity (duh), yellow is Solos (albeit frighteningly close and small), and green is Aenya, with the red meant to signify the side that always faces Infinity (the dark hemisphere). There is a point where the red side could clearly see the sun, rather than their light being provided through reflection off of Infinity, and this is what I’ve meant to highlight.

Infinity-Aenya model.png

As for the High Moon and Low Moon, the clarification given makes sense. There isn’t a whole lot I can say about the matter, I’m not too knowledgeable in how gravity would affect climate, but it would mean that the seasonal cycle would last as long as Aenya’s orbit does, something I’m sure you already know. 

As for the cycle, I understand that it is measured as the time it takes for Infinity to go from the north side of the sky to the south side. Now, in a polar orbit, this has the most simple explanation: Aenya is on the bottom during one part, near Infinity equator at the next, before being above Infinity, before continuing on its merry way to going back down underneath. However, you have stated that Aenya isn’t in Polar orbit (surprisingly so. At least the Zo didn’t mess up that bad). So, I will ask for more clarification on what exactly is meant by Infinity traveling from north to south in the night sky. What motion does it actually make throughout the lunar cycle? 

Saying we were in the dark hemisphere at the equator, always facing Infinity, we would see it north at an angle, but as time went on, we would see it come to our zenith (directly overhead), before heading down south, before stopping at another angle and heading back up. That motion creates a moon that goes from north to south. However, the way to cause this is very simple: Aenya’s orbit and its equator can not be coplanar. The more different they are, the more pronounced the effect is of Infinity going from north to south. At a zero degree difference, Infinity goes about in a straight line east to west (or west to east, I forget). At ninety degrees, it is a straight line north to south. At different angles, it will be some sine/cosine wave.

As far as I know, if this is how the cycle is meant to be described, that is how it would be created for Aenya. Do let me know if I have made a wrong assumption or misunderstanding. 


Matthew Andrew

Hi Matt,

Yeah, this is getting really confusing, but I appreciate the heck out of what you’re trying to do. 

I understand the polar orbit concept, it is pretty simple, but the problem is that I feel it would drastically alter the climate zones from latitudinal to longitudinal. As I am sure you know, the angle at which the sun hits our planet makes it so that the poles receive less sunlight, and on Aenya it’s no different. Northern cities like Northendell (duh) are very cold, whereas Ilmarinen (situated near the equator) remains balmy all year. So while the polar orbit is a really interesting idea, I do not think it works for the story. I have been trying to research this throughout the day and I did look up “Jupiter phases.” If you were standing on Europa and could see Jupiter going through lunar-like phases as we see of the moon from Earth, I think we could substitute that for a cycle.

Your map is convenient (thank you) but I am not sure how well it describes the situation. I have always accepted the fact that there are “twilight zones” between the hemispheres, areas between the two regions that are neither light nor dark, and in fact, this is where most of the life on the world thrives. So if you were standing on the edge of the dark hemisphere, I agree that yes, you would be seeing sunlight, and in fact, this is something that happens in the book when the heroes travel to a city near that edge. As you move toward the center of the dark hemisphere, where Infinity is full, you would be receiving less and less of the sun (same as it would on the “bright side” as well). I guess the question then becomes how much sun does Aenya get on its dark hemisphere with the sunlight hitting it at such an angle, or, more interestingly, what do the people living there see? I imagine it, though I could be wrong, as a kind of perpetual twilight hour.

Anyway, I think your little diagram should help clarify some things (you even got the colors right!). With your permission, I’d like to use it on my site. As for the Eon retrograde situation, I am considering making it a moon-moon (don’t you love this term?) if that fixes the problem.




The polar orbit concept, of course, would likely not be possible for Aenya. Sorry if I didn’t clarify that, but I was only drawing a comparison in my last message. What I was saying is that for Infinity/Greater Moon (they are synonymous, right?) to appear to bob up and down in the sky, the orbit would need to be at some sort of slant. It doesn’t need to be a large one or exaggerated (such as a ninety-degree polar orbit). I would draw it to clarify what I mean, but it would take a bit more time to display what I mean within a reasonable amount of time. I would need a day or two to do so, and my semester is starting soon, so I don’t know when I’ll have the time for such.

What I am trying to convey with the diagram is that the red zone will get some sunlight during some parts of the orbit. Furthermore, the twilight areas aren’t consistently in the same spots on the globe, since the globe rotates. Look at the picture again, the division between the green and red areas of Aenya is head-on with Solos (a bad thing for life) in some parts of the orbit and perpendicular to it in other parts. (as it should be). Furthermore, the light hemisphere would not even be able to see Infinity, as they would perpetually be facing away from it. It is possible that the twilight zones could get a peak here and there, especially towards the darker side.

Lastly, for Eon, I can not think of a feasible way to cause its apparent retrograde motion. As a moon for Aenya, it will only ever go one way in its orbit. As a moon of Infinity, the same. A simple solution is that this apparent discrepancy is caused by the viewer’s perspective (from the south it is viewed from right to left, as opposed to the north’s left to right). 

You may use the model I have provided, although do think about what I have said in the second paragraph, as I still believe the model contradicts what you intend for Aenya.


Matthew Andrew

Man, you gave me a great deal to think about last night. I think the biggest takeaway I got from our discussion is that I needed to better emphasize the gradient nature of the two hemispheres, because you would not have a natural boundary where one side is cold and dark and the other is bright and warm. Since an entire hemisphere takes up half the planet, it further dawned on me that, technically speaking, many of the locations in the story, including Ilmarinen (one of the most important locations), take place on what could be called the “dark side”. 

So, please check out my corrections/clarification, and let me know if you find any issues with it. 

The Twilight Boundary
The boundary between the dark and light hemispheres, the Twilight Boundary, is the most hospitable to life and where most of the story takes place. The precise range of this habitable zone is indefinite and changes depending on the planet’s orbital location and the time of year, though it is typically measured at 2000 km, from Nimbos in the West to Yefira in the East. Hedonia is located in the western hemisphere, while Tyrnael and Ilmarinen can be found in the eastern. During High Moon, when Infinity is most visible in the sky, the dark hemisphere creeps nearer and temperatures are at their lowest. Bogren armies stage annual incursions into the Pewter Mountains at this time.

Instead of hours, people on Aenya measure their day in passings. A passing is roughly 80 minutes, the amount of time it takes for Eon to cross the face of Infinity. You can imagine this like a giant clock in the sky. But the value of a passing is not always accurate, as the orbital speed of the heavenly bodies changes depending on location, viewing angle, and time of year. In certain parts of Aenya, people will refer to a half-passing or a quarter-passing.

The Day-Night/Eclipse Cycle
Because Aenya is tidally locked to Infinity, the eastern hemisphere perpetually faces away from the sun and toward the moon (or gas giant), while the western hemisphere faces away from Infinity. Nightfall occurs when the gas giant moves between Solos and Aenya, which is why night is sometimes referred to as eclipse. At dawn, the sun rises from the western horizon, and at dusk, eclipses behind the moon in the East.

Sunlight does reach the eastern hemisphere, only less frequently, with an exponential decrease in intensity as one moves east of the Twilight Boundary. The easternmost region of Aenya, the Dark Side, receives too little warmth to maintain a verdant ecosystem. Here, the Greater Moon dominates one-fourth of the sky and is considerably luminous.

The westernmost region of Aenya receives too much sunlight for life to flourish and is therefore referred to as The Dead Zones. This region consists of an arid plain known as The Great White Flat and a rocky desert called Ocean.


Hello again,

Your previous post last night was actually the thing I missed (I kept reiterating something you clearly already knew about. oops). I didn’t realize that the twilight boundaries were meant to be non-geographic.

As for the corrections you have listed, I do not have a problem with any of them. They all make sense to me. Personally, I think the exponential decrease of sunlight is a great addition, accounting for why the dark hemisphere is so different from the light hemisphere even though it gets some sunlight before its eclipse. Cycles also seem to make more sense now, as it is not dependent on Infinity’s position in orbit, but rather its phases. Overall, I think the issues and confusions I had have been fixed, and everything seems to make more sense.

Thank you for your responses,

Matthew Andrew

Now, dear Aenya fan, if you happen to own Ages of Aenya: Special Edition on your Kindle, you can download it again to receive this FREE update, incorporating everything discussed here, with a very special thanks to Matthew Andrew!

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