Eric James Stone, Nebula winner and “graduate” of NASA’s Launchpad workshop, joins us to talk about astronomy in our world-building.

We talk about tides, habitable zones, planetary orbits and axial tilts, stellar life-cycles, and other fun factors for authors to take into account. But obviously we can’t teach you everything you need to know about astronomy in 15 minutes, so we wrap with some handy resources for you to begin your continuing education:

•  Astronomy Picture of the Day
• Bad Astronomy
• Diamonds in the Sky

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Transcript

As transcribed by Mike Barker

Key points: knowing something about astronomy can help with world building. For example, tides affect fishing, the continents, and so forth. Habitable zones, the liquid water zone, are like Goldilocks — not too close or you get steam, not too far or you get ice, just in the middle. Contrary to popular thought, the seasons depend on axial tilt, not orbit.

[Mary] Season Seven, Episode 32.
[Brandon] This is Writing Excuses, Astronomy 101 for Writers.
[Howard] 15 minutes long.
[Mary] Because you’re in a hurry.
[Dan] And we’re not that smart.
[Brandon] I’m Brandon.
[Dan] I’m Dan.
[Mary] I’m Mary.
[Howard] I’m Howard.
[Eric] And I’m Eric.
[Brandon] We have special guest star, Eric James Stone, who has recently… You went to Launchpad, didn’t you?
[Eric] Yes. I went to the Launchpad workshop.
[Brandon] Will you tell us what that is?
[Eric] It’s a… Basically, it’s a workshop about astronomy for writers. It’s run at the University of Wyoming by Prof. Mike Brotherton, who’s an astronomy professor there.
[Brandon] Okay. Excellent.
[Mary] It’s NASA funded. I just also want to point out that Eric recently won a Nebula Award.
[Eric] A nebula is an astronomical term.
[Brandon] Yes, it is.
[Mary] Which is why I thought it was important to bring it up.
[Brandon] Eric is frequently published in Analog which has some very rigorous science required for most of its science fiction. He’s the best science fiction dude we know other than Howard.
[Howard] Oh, well, thanks, Brandon.
[Dan] Well, he’s also… He’s our Steve Martin, I think. He’s our most… He’s been on our show more than any other single guest.

[Howard] So, my pitch for this cast to Brandon… I was watching a documentary that was talking about the history of the Earth and the moon, and it pointed out that in this little dual planetary system we’ve got, because the moon is big enough to be a planet all by itself, the moon was originally quite a bit closer to the earth. This affected Earth in some really interesting ways. Including mega tides that swept across the planet. There was a lot of heat generated. Earth’s rotation changed. In looking at this, I thought, “Man. It would be so fascinating to have a story set on a planet where this is what’s going on. Where they’ve got these massive tides sweeping across the planet, and how do our colonists deal with that?” As I was thinking about that, I realized, you know, there’s got to be lots of other astronomy things… Planetary formation, solar system formation, nebula formation sorts of things, that would make for fascinating stories.

[Brandon] I do think that we don’t as writers, particularly as fantasy writers, know enough about this for when we’re generating our world building. I want to also focus this cast on what kind of astronomical things would it help us to know in our world building. Tides is one of them. Can you tell us anything about how tides work, Eric?
[Eric] Well, first off, the tides are generated mostly by the gravity of the moon, but also to some extent by the gravity of the sun. The sun’s a lot bigger, but it’s a lot farther away, so its effect on the tides is not as much. But essentially tides are something that you can calculate, once you start knowing the effect of the moon and the sun. People for thousands of years have been figuring out the best times to go fish based on the tides which are based on the position of the moon and the sun.
[Brandon] Okay. So how else do tides affect world building? Fishing…
[Eric] Fishing.
[Brandon] Do they have to do with the jets… The streams in the ocean, how they move and things like that? Do you know?
[Howard] Oh, absolutely. They shape continents. Over… On the mega-scale, the movement of the tides through different kinds of rock… There’s an awful lot of force involved in that water. If you look at the shapes of certain coastlines, a fairly steep coastline, the water only moves up and down the coast a little bit. But there are places in England, I think, where the tide coming in runs over like two or 300 yards, and you have these vast floodplains where it’s flooded and then un-flooded every day with essentially a massive salt sea.
[Eric] Yeah. In fact, there are a few places where the tide will come in faster than you can run.
[Dan] There is just one spot in England that today is all surrounded with dams and dikes and it just doesn’t really happen anymore, but for hundreds of years, it was just a giant swamp that would fill up and become a lake and then it would drain out and become a swamp. That played a huge role in British history. That’s all based on the tides.

[Brandon] So how quickly the tides come in and out is based on the moon’s orbit?
[Eric] Based on the moon’s orbit and the amount of gravity that it has. So if you had a world with a smaller moon…
[Mary] If you had a world with two moons…
[Eric] Bigger moon, closer moons…
[Brandon] How would, like… Could you… Can you imagine a tide that takes weeks to come in and go out instead?
[Eric] If the moon took…
[Brandon] Weeks?
[Howard] If the earth orbited a gas giant, so that we were very close to something very large, and then rotated a little more slowly so that the face of the planet… The side of the planet that’s facing whatever’s pulling on us is where high tide is… So the orbital period… Excuse me, the rotational period of the planet is essentially how you’re determining the period of your tides. So, yeah, you could totally do that. You just have to figure out what the gravitational pull of that planet… Of that gravitational center is going to be.

[Brandon] Okay. Let me throw some other questions at you guys. Our science dudes! Habitable zones? Let’s talk about those.
[Eric] Basically, around a star, there’s what’s called the habitable zone. It’s basically the liquid water zone. If the planet is too close to the star, then there won’t be any liquid water because it’s all turned to steam. If it’s too far away from the star, it all turns to ice. So in between those two places, there are… There’s an orbit… Well, a bunch of orbits where the planet can have liquid water. Since liquid water is essential to life as we know it, that means that’s where we could find planets that we could live on.
[Mary] You could call that the Goldilocks zone for obvious reasons.
[Dan] Yes. If a planet had like incredibly strong gravity exerting extra pressure on its water, would that change the size of that liquid water zone? Or am I misunderstanding my mechanics?
[Howard] Yes. But you’re coming at it the wrong way. If you look at… Well, let’s look at Jupiter for instance. Jupiter’s outside the Goldilocks zone, but Europa orbiting Jupiter… It’s been speculated that Jupiter’s exerting enough tidal influence on Europa that there might be liquid water under the ice of Europa, and there might be enough geothermal activity on Europa as a result of tectonic pressure, gravitational pressure, that there is heat and chemicals and whatever else and we might have life happening there in the ocean.
[Dan] So you can screw with this if you know what you’re doing, is the answer that I hear.

[Brandon] What about the orbits of planets? If you have an elliptical orbit, what does that do? Could you have one that goes in and out of a habitable zone?
[Eric] You could. So, obviously then you’d have a big long winter if you went out of it too far.
[Mary] Which I actually want to point out, George RR Martin’s series actually has good science if you pay any attention to it.
[Eric] Yes. Winter is coming.
[Mary] Winter is coming because he’s got a really wonky elliptical orbit. And, this is one of my other things that I love, there is no moon.
[Brandon] So there are no tides? Or they’re much smaller tides?
[Howard] Solar tides.
[Dan] Different tides. One of the things that I love about Westeros as a planet is that that incredibly long winter cycle that he has is the best explanation I’ve seen in a fantasy for why it has existed in this same kind of medieval technological level for like thousands and thousands of years. Because it keeps coming back and knocking them down again every time they tried to do some serious technological progression.
[Howard] Well, it’s not the first time it’s been done, either. I don’t remember the name of the author, but the books were Helliconia Winter, Helliconia Spring, Helliconia…
[Brandon] I think the Summer Queen and the Winter Queen by Joan Vinge also were dealing with this same concept.
[Dan] Cool.
[Howard] Yeah, they both explore… I think in the Helliconia books, there were two stars and an orbit that… And, yeah, a 400 year winter.

[Brandon] Okay. Let’s stop for our book of the week. Then I’ll have another question for you guys. Howard actually is going to give it to us.
[Howard] Yep. I just took a moment to look this up and make sure it’s available on audible. Helliconia Spring, the Helliconia trilogy, book 1 by Brian Aldiss narrated by Christopher Slade. I read this… Gosh, 20 years ago. 20, more than that, years ago in college. And really loved the concept, the astronomy behind it. And how those long winters… Really long winters, really long summers affected the natural life, the flora and fauna, and affected culture. It was really, really fascinating. I don’t know how memorable characters are, because I can’t remember any of their names, but hey, it’s been 20 years.
[Brandon] That’s okay. Where can they get it?
[Howard] Oh. Head on out to audiblepodcast.com/excuse. You can kick off a 14 day free trial membership and download a copy of Helliconia Spring by Brian Aldiss narrated by Christopher Slade for free or pick up any other audiobook that suits your fancy.

[Brandon] Okay. Next question for you then is what happens… Oh!
[Mary] Actually, before we do that, before we leave seasons, one thing that we should talk about because this is a common misconception is what effect the orbit of the planet has on the seasons.
[Brandon] Okay, yes. Good. Eric?
[Eric] For Earth, actually, it has very little effect. What causes our seasons is the axial tilt of the Earth, not the distance from the sun. For us, actually, the northern hemisphere is farther away during the summer, farther away from the sun during the summer than during the winter, but it’s because of the way the planet’s tilted that our seasons are the way they are.
[Brandon] So what does that do?
[Eric] Basically, during the summer, the… We’re tilted such that the sun’s rays are coming sort of directly at the northern hemisphere.
[Mary] Yeah, they aren’t having to travel through as much atmosphere.
[Brandon] Ah, so it’s angle?
[Eric] It’s the angle.
[Brandon] Angle creates our seasons.
[Mary] There’s a really great story by Geoffrey A. Landis… And I can’t remember the name of it, but it’s in the Diamonds in the Sky anthology which came out of the Launchpad initiative. It is… It specifically deals with seasons. It’s great, because there’s a king who wants to change how long summer is. So he tries to move the planet, which has exactly the… It’s a great book. [Garbled — Approaching Perimelasma?]
[Brandon] Great.
[Eric] So if the tilt of the earth were essentially straight up rather than about 23 degrees at an angle relative to our orbit around the sun, we would have no seasons. If we were tilted at 90 degrees, we’d have some very radical seasons.

[Brandon] Interesting. See, that’s the sort of stuff I wanted to get in this podcast. That’s great. What happens if we change our star? Binary stars, gas giants, whatever those other wacky little ones are, what does that do to our habitable zone, what does it do to our planets?
[Howard] One thing to keep in mind is that the star that we currently go around… The best science indicates that the star we go around is a nice stable long-lived one. A lot of the other options are not particularly long-lived and are not particularly stable. Their output varies a lot over time. When we look at the age of the earth and how long it took life to form, it might be a real challenge to get life to form around a blue giant even if you were in the habitable zone because about the time life’s evolving, it’s exploding.
[Eric] One of the interesting things about it is that the bigger the star is, the faster it burns through its fuel, and the shorter the life it has.
[Brandon] Bigger stars, the habitable zone will just be further away?
[Eric] Yeah. It’s… Because they’re hotter…
[Howard] Further away and won’t last as long.
[Mary] Yeah. But… Which also means that your year is going to be significantly longer, which is going to have an impact on your seasons as well because of the axial tilt.

[Howard] Another concept when we talk about habitable zones, is on the mega astrometry side of things, it’s been postulated that there is a galactic habitable zone. The closer you get to the galactic core, the more likely you are, because there are just more stars there, the more likely you are to be exposed to gamma ray bursts from large stellar sorts of events. Those are the sorts of things which if they’re in the local neighborhood would just kind of sterilize the planet. Then further out, there have been fewer of these events, and so you’re less likely to have useful things like carbon and iron and gold and nitrogen all in the same place. They’re a little more element-poor out towards the rim.
[Dan] Poor life that doesn’t revolve on a planet with gold.
[Howard] So sad.

[Dan] Now I… We asked about binary stars. I want to make sure to hear about that. Ever since we watched Star Wars as a kid, Tatooine has two suns. Is that possible? What does that do to a planet?
[Eric] It not only is possible, they just recently spotted a planet that was orbiting a binary star.
[Brandon] Okay. Will it still have a habitable zone?
[Eric] Oh, yeah.
[Dan] Does Luke Skywalker live there?
[Brandon] What will it do? Anything?
[Eric] Well, it will probably give you some interesting temperature variations, as the suns… Depending on how your orbit is, the suns would eclipse each other and things like that.
[Brandon] You will orbit not one of the suns or the other, but the point between them of the gravity or something like that… Like…
[Eric] Well, it’s possible… Depending on how close the stars are to each other, your orbit might be different. You might just orbit one of them and the other one is kind of like Jupiter, out there and orbiting around. Or you might be orbiting both of them. I… As far as I know, no one has shown a way to have a figure 8 orbit around both stars that is stable. So that’s one probably to steer away from.
[Dan] That would be awesome, though.
[Mary] Let me toss another book in there which plays with multiple suns. That’s Nightfall. Which is…
[Brandon] Wonderful book.
[Howard] Short story by Isaac Asimov.
[Dan] Also Pitch Black with Vin Diesel which we talked about before.
[Mary] But it was expanded into a novel, and the novel really gets into great detail.

[Brandon] Okay. I really want to do more of this. I really want to have you back, Eric, to do more science stuff. This has been a great podcast. Can you give us a writing prompt?
[Howard] Well, before we do writing prompts, can you think of… Let’s throw people at some astronomy resources online. One of my favorites is the astronomy picture of the day. They have an RSS feed. Mostly…
[Dan] They have an app for smart devices.
[Howard] It’s a pretty picture with a paragraph below it describing it and it’s full of links. If you use that as your research jumping off point for astronomy for the day, you will fill your head every day with fun astronomical things.
[Mary] I’m also going to pitch Diamonds in the Sky which is an anthology of short stories that are designed to teach astronomy literacy.
[Brandon] Oh. That’s cool. That’s a really great idea.
[Eric] I want to mention the Bad Astronomy website, which is a great resource, not only for clearing up some misconceptions, but also for learning about new developments in astronomy.
[Mary] And he’s a funny writer.
[Brandon] Yeah. He’s a good writer. All right. Writing prompt?

[Eric] Writing prompt. Write about a world that your space colonists are going to that has a different axial tilt from Earth, and try and figure out how that affects the seasons for it.
[Brandon] Okay. Thank you very much, Eric. This has been Writing Excuses. You’re out of excuses, now go write.