Galactic Geography — Science Fiction Using Real Stars

Galactic Geography: How Important Is It to a Story?

Galactic Geography: Milky Way arch
Milky Way arch gives a quick view of galactic geography. Magellanic Cloud satellite galaxies appear on the left. Photo: Bruno Gilli, ESO (CC BY 4.0) trimmed. Click on the picture for larger view.

Galactic geography is likely not the most vital part of any story. Most of us can enjoy any story that’s well-written, with good dialogue, good character development and an interesting plot. But there are some aspects of place and details that can break a story, too.

If an author places Paris (the capital of France) in Botswana, he or she may not be taken seriously. Flubbing details like this show rank ignorance on the part of a writer. Some facts are not as important. This involves the realm called “artistic license.” Great artists ignore facts and get away with it, because the bulk of their work is so well done, minor details are dismissed as unimportant.

In the short science fiction film, Quest, by Saul Bass, the orbits of moons around a planet defied realistic orbital timing. Outer moons moved just as quickly as inner ones, contrary to the laws of physics. But the visual effect was stunning. Quite a number of things in this film, based on a Ray Bradbury story, did not make literal sense. But they worked visually. And the producer, Saul Bass, was known as a consummate graphic designer, with two Academy Awards for his work on films.

Getting geography right is one of those things that readers may or may not care about, depending on their level of education, intelligence and the quality of the story. New Zealand attacking neighboring Denmark would likely be seen as a gross error by most readers. The two nations are on opposite sides of the planet—as far apart as you could make them. They’re not neighbors. Of course, if the story is taking place in an alternate universe, then a great many things are up for change.

Getting galactic geography correct is likely not as important to many readers, because they merely don’t know any better. But a growing number of hard core science fiction buffs are becoming increasingly smart about galactic geography.

How Science Fiction Can Get Galactic Geography All Wrong

There are several ways a science fiction author or screenplay writer can get galactic geography all out of whack. They can do this by,

  • Choosing a star system which cannot possibly support the planet being described,
  • Disregarding the relative positions of stars with each other, and
  • Ignoring the motions of stars over time.

Galactic Geography Error: Stellar Motion

This last item (motions of stars) I happened to notice in a short story by David Brin. He had used a known and named red dwarf in a story which took place over a long span of time—something like millions of years. The big problem was that, at the beginning of the story, that star would not have been anywhere near the main scene (Earth’s neighborhood) so long ago. The relative motion of stars as they orbit the galaxy would have made the position of that star many tens of thousands of light years away. Oops! And this by a graduate of astronomical science.

Helpful guy that I am, I wrote Brin and let him know that I love his writing and enjoyed the story, but thought he might want to know about this minor error. His reply was less than cordial; he implied strongly that I had killed one of his children. Oh, well!

Yes, his error in galactic geography had been a minor point—one that few others would have noticed. But I would have wanted to know about such a thing if I had made a similar error in one of my own stories. I like getting details like that correct, even if such points of galactic geography are minor.

Galactic Geography Error: Choosing the Wrong Star System

Galactic Geography: Stars in the NeighborHood software focused on Canopus.
Galactic geography is the specialty of Stars in the NeighborHood software. Here, the focus is on the super-giant star, Canopus. Click on the picture for full view.

A slightly more important point involves choosing the right kind of star. Part of galactic geography includes the qualities of a particular location. Like locations in earthly geography, stars have their own ages and chemistry. These are easy to look up.

For instance, having indigenous life on a planet orbiting a super-giant star, like Canopus, is a fairly serious error in galactic geography. Why? Because any star which has entered its giant phase has already left its adulthood and entered its life as a senior citizen of the galaxy. Giants are far brighter than their “main sequence” adult counterparts. This means that any planet upon which life might tend to evolve would have long since been fried.

During its main sequence (adult) phase, Canopus would’ve been about 2,200 times brighter than our own sun. Why so much brighter? Because Canopus has about 9 times the mass of our own sun. Greater mass means hotter core and brighter output. In the Dune story series, Canopus is the home of the planet Arrakis, also known as “Dune.” It’s a desert planet, but hold onto your seat, because the amount of warming might shock you. If Arrakis had been similar to Earth in its youth, when life started to evolve, the light from giant (senior citizen) Canopus would be 15,100 times the light of our own sun. In other words, Arrakis would be receiving nearly 7 times the light it received during the main sequence of its sun, Canopus. Yikes!

To make matters worse, a massive star also burns up its fuel far faster than a lighter weight star, like our sun. Our own sun will stay in its main sequence something like 10–11 billion years. Canopus stayed in its main sequence for something like 41 million years. At 41 million years old, our own planet Earth was still being bombarded by debris from the stellar disk of formation. In other words, Earth was not yet fully formed. Life took something like 3 billion years to gain a solid foothold—more than 70 times longer than Canopus’ stay in the main sequence.

Naturally, the story, Dune, was wildly popular. The story itself overshadowed such problems as galactic geography. Still, for all the research Herbert did on every other aspect of his story, he could have spent a little more time on his stars to get his locations right. After all, a writer shouldn’t place a jungle scene in Alaska or a polar scene in Florida, all other things being equal.

Another factor for life involves the chemistry of the star and its possible planets. If a star system is largely hydrogen and helium, planets will likely be gas giants, because there will not have been enough iron, silicon, oxygen and other elements to form Earth-like worlds. This involves something called the metallicity of a star, frequently measured as a ratio of a star’s iron content compared to the iron content of our own sun—a ratio that’s sometimes called “Fe/H.” This was not a big problem for Canopus which is only slightly metal poor compared to Sol—with an Fe/H of about –0.07.

Galactic Geography Error: Stellar Variability

Galactic Geography: graph of Mira light curve.
Graph of light variability for the star, Mira. This star is one of the beacons of galactic geography. Courtesy American Association of Variable Star Observers (AAVSO). Click on the graph to view source. (Retrieved 2016:0627)

This is an extension of the “choosing the wrong star system” type error.

Both the original Star Trek television series and the Next Generation series used Mira (Omicron Ceti) as a prime location for a story. In the original series episode, “This Side of Paradise” (1967), planet Omicron Ceti III was the home of a Federation colony. In the Next Generation episode, “Conspiracy,” planet Omicron Ceti V (Dytallix B) was an abandoned mining world.

So, what was so wrong with using Omicron Ceti?

Mira is an extremely variable star—a giant M7 III, with swings in visual magnitude from 10.1 to 2 (a difference of 8.1 magnitudes of brightness) in an average 332 days. That’s a difference of 1,738 times in brightness. Any world orbiting such a star would alternately be scorched and frozen.

Galactic Geography: Mira in software
Mira is so much a part of the galactic geography, it is included in the Locator Cube (right panel) of Stars in the NeighborHood software. Here, the focus is on Mira. Click on the screen shot to view full size.

Even if a world enjoyed brief warmth comparable to that of Earth, most of its year would be spent frozen. It would be like enjoying the full brightness of our sun for a few short days, but after a period of a few months, finding ourselves looking at our sun as if we were standing on Pluto. Know this: temperatures on Pluto never get above –219 °C. Our luckless planet would likely never get this cold, but it might come close, especially during the first few months after apastron (farthest distance from its primary star).

As with the Canopus problem, Mira might have had a planet where life could have started to evolve. But the grass and trees shown in the original Star Trek episode are an impossibility, at least for natural growth.

Wyatt and Cahn (1983) estimate a mass of 1.18 times that of Sol (our sun). They also estimate an age of about 6 billion years. Any Earth-like planet would now likely be lost to the body of Mira, swallowed as the star left its main sequence and ballooned out to become the giant it is today.

Outer planets, safe from being swallowed by Mira as it had swelled into its giant phase, would never have evolved life as we know it. They would have been too cold during Mira’s main sequence adulthood. So, Star Trek’s Federation colony was an impossibility.

Galactic Geography Error: Relative Stellar Positions

Galactic Geography: Klingon staging snafu
This view in the software shows a major military snafu. When the Vulcan High Command chose Regulus as a staging area for an attack on Procyon, they would have to go through Klingon territory to get there. This shows poor knowledge of galactic geography. Click on the screen shot to see full size.

The positions of stars are a far more important point. Why? It’s so easy to get it right. So, why would anyone get it wrong? One big reason is laziness, especially with the internet and so many resources online.

Gene Roddenberry and his Star Trek writing crew got galactic geography wrong on a number of occasions.

In the Star Trek: Enterprise episode, “Kir’Shara” (2004), for instance, Regulus (Alpha Leonis) was used as a staging area. What made this choice particularly bad is that the Vulcans were preparing for a massive pre-emptive strike against Andoria in the Procyon system (one conflicting source places Andoria in the Epsilon Indi system, relatively close, but equally bad for the same reason).

The screen shot from Stars in the NeighborHood software shows two big problems with such a plan. Star Trek tag files were used to mark those star systems mentioned in the Star Trek universe. As you can see, Regulus (the staging area) is on one side of the Klingon homeworld, while Procyon (the target) is on the other. That’s like the Americans during World War II using Switzerland as a staging area for an attack on Japan. Oops!

Galactic Geography: Procyon neighbors
This shows a list of Procyon neighbors which would have been far better choices for staging areas. Click on the screen shot to view full size.

Putting all your resources in one area surrounded by one set of enemies (Italy and Germany, in our example) is not the smartest thing to do, especially when your target is so very far away (Japan). The destination of that Star Trek pre-emptive strike is a whopping 71.4 light years from the staging area. Groan! A staging area is supposed to be somewhat close to the target of attack. And during the era of Star Trek: Enterprise, the Klingons are the enemy.

You don’t need a star system as a staging area. There are a near infinite number of points in 3D space at which to converge your forces in preparation for an attack. A star system, of course, gives a visual anchor for such a gathering, but that’s unimportant with savvy navigation skills. Regulus is only 16.21 light years from Omega Leonis (system for the Klingon homeworld, Qo’noS). So, they would have to go through Klingon, enemy territory to get to their destination. Not very bright.

There are several star systems within 10 light years of Procyon—far closer than Regulus:

  • Gliese 234 AB—4.6 light years
  • Sirius AB—5.25 light years
  • Gliese 273—1.11 light years
  • Gliese 1111—5 light years
  • Gliese 1116 AB—8.12 light years

If a writer breaks any of these rules, it’s not a bad idea to have an explanation for why the rules are broken. And, if you’re like me, galactic geography is fun.

Special Thanks

A special thanks to Gary York for suggesting that Stars in the NeighborHood software could be useful for getting galactic geography right in writing science fiction. Though this idea had occurred to me and several others years ago, his timing was perfect. I was now ready to explore this idea in greater depth. So, thanks Gary for impeccable timing.

This article was originally published 2016:0628 on