By  Michael James Liljenberg.
Creating Fantasy and Science Fiction Worlds
And God said, "Let there be lights in the expanse of the sky to separate the day from the night, and let them serve as signs to mark the expanse of the sky to give light on the earth." And it was so.
Day 4: Let There Be Lights in the Sky: Astronomy & Time
As the day begins on the fourth day, it begins in a new way, with the rising of a huge golden light hanging in the sky. Now God begins to populate the world he has made, first by populating the day and night with lights in the sky. There is some evidence that the ancient Hebrews considered the stars and planets angelic beings. According to the Creation narrative in the Bible, the function of the sun, moon, and stars is to give light to the earth and to mark time. The passage of months, the cycle of the seasons, the ebb and flow of the tides all depend upon the motions of the lights in the sky. A common issue overlooked in many science fiction universes is different orbital and rotational speeds different worlds would have.
One of the reasons we know Tolkien's Middle Earth is supposed to be our Earth is that the moon operates the same, and several times he describes the constellations Orion and the Big Dipper (though he gives them different names). On the other hand, we know that the world of ElfQuest is not exactly the Earth we know because of its two moons.
Remember the scene in The Lion King where Simba, Timon, and Pumba are lying back looking at the stars. Pumba thinks they're "big balls of gas, burning billions of miles away." "Pumba," Timon remarks, "with you, everything's gas." Maybe in your world the stars really are the "great kings of the past looking down on us". I am reminded of the line from C.S. Lewis' Voyage of the Dawn Treader when Ramandu, the retired star, comments that burning gas is "not what a star is but only what it is made of."
An example of something else to avoid, I was recently reading Brian Jaques' book Salamandastron, one of the Redwall Abbey books. The book follows four parallel plot lines. In three separate chapters - each supposedly happening at the same time as the others - the moon is described as "full as a plate", first quarter crescent, and half. The phases of the moon go well with the specific scene in which they appear, but the sub plots are supposed to be simultaneous. It really jarred me out of the story.
In many pre-industrial societies calculating the date by the phase of the moon is second nature to people, as is knowing the tides. Most ancient societies held the night sky as an object of worship. They meticulously plotted its patterns and changes to the point of being able to predict eclipses and conjunctions, usually for the purpose of making astrological predictions. Stars and planets become associated with gods and goddesses, and by association the cities, countries, or even specific rulers who worship them. In a sci-fi/fantasy world, those threats may be more than symbols. In the Annn McCaffery's Pern series, the Red Star is the source of the "Thread", spores of some sort of voracious fungus that can survive interplanetary space and atmospheric re-entry.
In your world you may want to develop a whole star chart, mapping out the various constellations, the stories, myths, or "real" history that goes along with them, and how they figure into your magic and religious systems. Is there a north star? More than one sun or moon? Significant planets? What if your world is actually the moon of a huge gas giant? How would the rings and other moons figure into the other aspects of your worlds?
Needless to say for Science Fiction writers, this can be a very important topic. You should probably do some research into astronomy and planetology. A good place to start is magazines like National Geographic and Popular Science, both are written for the general audience (and they can be found free at most public libraries). Televised science documentaries, like Nature, Nova, and Scientific American can often give you detailed glimpses of front line scientific developments and theories.
Suns
If you've ever looked at any book on astronomy, you've probably seen this Hertzsprung-Russell diagram cross-indexing a star's Magnitude (brightness) with its temperature.
Stars are generally typed by color using the letters O, B, A, F, G, K, M. The letters are sub-divided using the numbers 0-9. (The sun is a type G2 star) Most stars fall along the line from the upper-left of the diagram to the lower right, called the "main sequence". Main sequence stars burn hydrogen into helium. Giant stars have burned up all their hydrogen and are now fusing helium and heavier elements which makes them expand to huge sizes. White dwarf stars are the burned out cores of novas.
Type O stars are very blue in color and very hot (35,000 C about 6 times hotter than the sun). Any worlds orbiting a star like this would have to be very far away (with very long years) to not be burned to a cinder.
Type B stars are also very hot (21,000 C almost 4 times hotter than the sun) both O and B stars are so hot because they are fusing their hydrogen quickly. They tend to cluster together in areas of star formation which means they are usually too young to have planets, and their powerful solar winds tend to blow away the congealing dust clouds that would have formed planets.
Type A stars are white and about twice as hot as the sun. Sirius, the brightest star in our sky is a type A star. If the sun were a type A star Mars and the asteroid belt would be in the Optimum Life Zone, Mercury would literally melt, Venus' atmosphere would be blown away by solar wind, and Earth's water would boil away. The point is, that if a world in your story is around a type A star it would have a very long year, and the ground would be bathed in higher levels of UV radiation than the Earth is. Another group of type A stars includes the white dwarf stars that are the collapsed cores of red giants. They usually sit in the core of a planetary nebula. If there were any worlds around a white dwarf they would have to have formed since the star's nova. They would be exposed to a lot of radiation.
Type F stars are creamy in color and only a little hotter than the sun. Again, worlds around type F stars would need to be further away from their sun and have longer years.
Type G stars, like our Sun are actually rather rare stars. They are very stable in age and radiation output, and so, are the most likely stars to have habitable worlds.
Type K and M stars fall into two groups. In the main sequence these stars are small and cool. They burn very slowly, are usually much smaller than the sun, and are the most common kind of star in the galaxy. Worlds around such stars are cold, unless they are quite close (and therefore have a very short year). The other type K and M stars are the Giants and Supergiants. These stars have burned up all their hydrogen and are now burning their helium. This causes them to expand to hundreds of times their original size. When the sun goes into its giant phase, it will engulf Mercury, Venus, and the Earth. So any habitable planets around a Giant star would likely be the moons of the gaseous planets further out from the star.
Most stars in the universe exist in groups of twos and threes. Binary and trinary star groups are unlikely to have worlds, because their dueling gravitational fields tend to prevent planets from forming, and any that do tend to get sucked into one star or the other, or shot off into space. It is not impossible, however. The closest stars to the earth (Alpha and Proximia Centauri) are a trio of stars. Alpha Centauri A is a G2 star like the sun, but slightly larger, and Alpha Centauri B is a slightly smaller type K star. They orbit each other every 80 years coming as close together as 11 AU (about the distance between the sun and Saturn) and as far apart as 36 AU (about the distance from the Sun and Neptune - 1 AU is the distance from the earth to the Sun). It would be possible for small rocky planets to exist in orbit around the two stars without the other star pulling them out of orbit. If the earth was a world in orbit around Alpha Centauri A, Alpha Centauri B would appear to be a visible disk at it's closest, bright enough to be visible during the day and just a very bright star at it's farthest.
To have a world with multiple suns, like Tatooine in Star Wars, or the triple suns of the world of the Dark Crystal the stars would have to be almost ludicrously close together and the planet would have to be in orbit around both stars
But, again, you are the creator of your universe. You don't have to scientifically explain the orbital paths of the stars, or gravitational forces, or any of that. You can make worlds where the star is old, huge, and red. You can make a world with two suns so bright that for a quarter of the year there's one sun visible during the day, and the other is visible most of the night.
Planets
Even in fantasy stories where you don't have travel to other worlds, planets often have religious or magical significance. They are primary symbols in any astrological chart, and they are often associated with particular deities. The Greeks and Romans named the days of the week after the 5 visible planets, and the sun and moon. So recall your theology and magic from day one and look for areas to integrate
Planets come in two basic flavors, terrestrial or rocky planets, and gas giants. Terrestrial planets tend to form close to the sun since the sun's gravity pulls the heavier elements they are made from closer in. Gas giants form further out from their sun, as any hydrogen close to the star will either get sucked into the star, or solar wind will push it out to about Jupiter's orbit (for a sun sized star). Gas giants also tend to form out past the ice-line, the line past which water in space will freeze. So most of the time a Gas Giant will be well out of the Optimum Life Zone (OLZ). The OLZ is the distance from a sun where a planet can sustain water in all three states, liquid, vapor, and ice. It is conceivable that the moons of a gas giant could sustain life if the star made the transition to a red giant and warmed the moons enough to melt the ice. You might also be able to include a third type, ice, like Pluto or Jupiter's moon Europa. They aren't exactly rocky worlds, but they are solid.
For planets there are too many variables to reduce them to a simple group of classes. Variables that affect a planet and its ability to support life:
Orbit:
How far away from the star is the planet and how long is one year. This also involves how elliptical the orbit is and the orbit's inclination (the tilt of the orbit above or below the plane of the solar system). Pluto was recently "demoted" to "dwarf planet" status, because unlike the "real" planets in the solar system, Pluto's orbit is both well outside the elliptical plane (27°) and while the other planets have nearly circular orbits, Pluto's is so elliptical, it overlaps Neptune's.
Rotation:
How fast does the planet rotate? How long is one day?
Size:
How big is the planet?
Density:
Planets with lower density will have weaker gravity for their size, fewer metals, and more water and organic chemicals. Denser planets will have larger amounts of heavy metals, like lead, mercury, gold, and uranium (and be more toxic to organic life but more attractive to mining consortiums). Saturn has so little density it would actually float on water
Gravity:
How strong is the surface gravity? This, of course is a function of the size and density of a planet. Gravity will affect life on a planet in many ways. Planets without enough gravity will not be able to hold hydrogen in the atmosphere, and eventually all water will disappear. Planets with very strong gravitational pull will have very high air pressure at low altitudes. Planets with high gravity will tend to attract moons (and comets and asteroids). Planets with lower gravity will be affected by tidal forces from their moons, other planets, and their sun more. Planets with high gravity will require ships in orbit to travel at much higher speeds.
Axial Tilt:
Seasonal weather patterns are affected by the axial tilt of the planet and by the planet's distance from its sun. The more extreme a planet's tilt, the more extreme its weather. The more eccentric its orbit the more extreme its weather will be. The earth's orbit is nearly circular, but its closest point to the sun is very near the beginning of winter in the Northern Hemisphere. This means that, generally, winters are more mild in the north, though not by much. And that summers tend to be a little cooler in the north. This is effect is mediated by the huge stretches of ocean in the Southern Hemisphere.
Magnetic Field:
Magnetic fields protect planets from solar radiation. They will also affect spacecraft in orbit, disrupting communication links, shields, and weapons fire.
Tectonic activity:
How geologically active is the planet? Are there a lot of earthquakes and volcanoes? Geologically active planets will have more rugged features, higher mountains (which create more extreme weather around them) .
Atmosphere:
What gasses make up the atmosphere of the planet? How breathable is the air? What kinds of organisms will thrive and what kind will struggle?
Magical Fields:
How does your magic system interact with a planet? Are there magical energy fields or lines of force? Do they disrupt or improve the creatures or societies that live in them? Do certain divinities, magical, or even physical laws apply on certain worlds?
Moons:
Moons are planet and planetoid sized bodies orbiting a planet. They range from irregular asteroids only a few miles across to worlds even larger than the Earth. There could be moons out there even bigger. Maybe even somewhere there are moons with moons.
Moons can affect a lot of different aspects of a civilization. Moons of sufficient size affect the tides of seas and oceans. Their phases mark rhythms and patterns of nature and social rituals. Many mythologies associate our moon with females because of its monthly cycle. Moons could be part of a mystic cycle where certain conjunctions split the boundary between the physical and spiritual world. Maybe one of the moons is an artifact of an ancient civilization.
Rings:
Rings appear to be a feature exclusive to Gas Giants. Planetologists are still trying to figure out exactly how they form and how so many small objects in such a dense pattern keep a stable orbit around the planet. The bright ones around Saturn and Jupiter are made up of ice particles, so the should only exist out past the ice line. But the rings around Uranus are made up of very dark material, probably containing carbon. So there isn't any reason you can't find an excuse to put rings around your planet. Can you imagine what impact rings in the sky would have on your world's magic system or mythologies?
Of course the fun of making up your own world is that you can create whatever you want: a world where everyone has to live under the ground because their sun has become unstable and is now cooking the surface with radiation. How about a world suspended between two planets so that everything is weightless? You could create floating continents in the clouds of a gas giant like Flash Gordon's planet Mongo.
Bonus Worksheet
I've put together a PDF of a solar system worksheet that will give you a quick reference for all the planets in a solar system.
Stars
Yes, we've already gone over star types and all that and I haven't even scratched the surface of supernovas, black holes, galaxies, neutron stars and all of that. But the point of this tutorial is not to make you all astronomers, but to help you create worlds for you fantasy and science fiction stories.
For the most part, the stars serve as a backdrop. You may want to create (or re-name) constellations with special significance to your characters or to the cultures in your story. Are they part of astrological signs that influence, signify, or even predict events in the world of your story? Are there signs in the sky, like a rouge star, that grows in power as the evil emperor gains power over the world? Are they affiliated with gods, angels, or spiritual powers?
So, as the sun sets on the fourth day, consider what role do the sun, moon, planets and stars have in your universe.
http://www.projectrho.com/starmap.html links to many programs for building 3D star maps
Introduction
Day 0: Theology
Day 1: Physics
Day 2: Weather
Day 3: Geography
Day 4: Astronomy & Planetology
PDF: Solar System Worksheet
Day 5: Animals
PDF: Ecoshpere Worksheet
Day 6: Man (& other races)
Part 1: Culture
Part 2: Economics & Government
PDF: Civilization Worksheet
Day 7: The Rest - of the Story
References
http://hiddenway.tripod.com/world/ an index of site for creating fantasy and science fiction worlds, from mapping software to academic papers on population growth.
FARP Article Guestbook
| Date | Name | Comment | | | 16 Sep 2006 |  Chris D | Wanted to tell you what a great job you did on this chapter. Can't wait to read the next one! | |
| 2 Oct 2006 |  H. England | Yessssssssssssss!!!!!!! I've been waiting for these others to be published! Thanks for putting them here. They're so helpful to me! | |
| 14 Oct 2006 |  Gwyn C R Rees | Wow! Not only informative for the discerning SF writer, but a great introduction to astrophysics. Takes me back, that Hertzsprung-Russel! The detail you've gone into is really commendable. Good job well done. | |
| 28 Oct 2006 | Nick the ripped | Oh my god!!!! My finger is stuck to my hand!!!!!!!! | |
| 9 Jan 2008 | Pablo Luna | You may like to download Celestia from http://www.shatters.net/celestia/ and Stellarium from http://www.stellarium.org/ to see stars in 3D so you have a good perpective of how things would look in your story. | |
 Back to the FARP main page.
 The collection of art and writing tutorials in the Elfwood Fantasy Art Resource (F.A.R.P.) is a part of Elfwood.
The FARP logo was created by  Miguel Krippahl (The muscular guy in the FARP-logo) and  Thomas F Abrahamsson (The text and general graphic design). Those sections written by volunteers are copyrighted to Thomas Abrahamsson and the respective writer. Elfwood is a project created by Thomas Abrahamsson. All rights reserved. Unauthorized Reproduction of the graphics, writings, and materials on these pages is absolutely prohibited! You may consider all material on these pages protected and copyrighted, unless otherwise noted. You may NOT use the images found at the FARP or Elfwood pages on your home pages! All of these images are copyright protected! Everything you see here represent the collaborative effort of the Elfwood community and Thomas Abrahamsson. Please read the Legal Disclaimer for more info on warranties/etc for these pages!
|
