Fantasy World Building: Star Systems and Other External Influences
Correlations in Fantasy World Building
Imagine a world dominated by Vampires. This species of Vampire finds it difficult to survive in the sunlight particularly on the surface of the world which exists in a binary star system. Even when darkness descends on the planet every 3115 days for 23 days, the twelve moons still make living on the warmer surface of this world difficult as reflected sunlight is still harmful.
The planet exists in the perfect climate for life to exist on the surface and a humanoid race has thrived upon the surface of the planet, their numbers are have risen into the millions since the last darkness came. The vampires who live in caverns beneath the earth with other light effected creatures are slowly awakening from the sleep to look into the modern world of their ripen cattle.
In this world, the two suns work against and in favor of the Vampire forcing them to live in a society far beneath the surface of the world, while providing them with a feast above the surface every few thousand years flourishing the food supply and sustaining the Vampires.
Sun and Vampires -1
Beyond your Fantasy World
Earth would not exist without the Sun. The Earth is dependent upon its external influence. Likewise in fantasy world building, fictional worlds also have external influences. Recording the relationships between your fantasy world and its external influences will help to provide your world building with substance and provide your audience with correlations for your world's characteristics and circumstances.
Without our Moon and Sun we would not have tides and the darkness of the night would be darker, more so without any distant stars. The Sun is the most influential terrestrial being in our sky. It provides the Earth with much more than just sunlight, heat and a basis for recording the passing of time.
If your fictional world is a planet or other arterial body in a traditional setting then the sun or suns which interact with your world will have a strong influence. Even if your world is not a traditional fantasy world, the concept of external influence will still apply.
Gathering information about the external influences of your fictional world provides a fictional world builder with valuable information about the cause and effect orelationships upon their constructed world. It is useful to know what the sky looks like at any time of the day. It can also help to provide credibility and continuity for plots and other background developments.
If your world was a computer generated program, which external influence would you consider most important?
Birth of a Solar System
The first 'truly' habitable planet candidate found in the Goldilocks zone (not to hot and not to cold) was announced by astronomers in September 2010. The planet Gliese 581g is located about 20 light years away from Earth.
More recently in February 2011 astronomers announced that by using Nasa's Kepler telescope a total of 54 planet candidates located in the habitable zone of Suns have now been discovered with five potential earth-sized planet candidates that may support water and possibly life. 
The Sun's Influence on your Fictional World
A solar system is a system with one or more stars. Your fantasy world can exist inside a system with multiple stars with varying ages and sizes. When a star explodes or implodes it will have a large impact on the rest of your system but until then, your fantasy world might enjoy a relatively disaster free period in which your fantasy world could support living creatures with developed cultures .
A sun can be born out of the "dust and debris left behind by novae and supernovae eventually blend with the surrounding interstellar gas and dust, enriching it with the heavy elements and chemical compounds produced during stellar death. Eventually, those materials are recycled, providing the building blocks for a new generation of stars and accompanying planetary systems."(1)
If your fantasy world follows a similar tradition and foundation of life as our own planet then life will exist where water exists. The number of suns in your fantasy world's solar system will not be as important as the distance of your world from the suns. Ensure your world is located in what astronomers regard as the "Golldilocks" zone. When creating your solar system map out an orbit of your planet around the Suns so that you can determine the closest point your world comes in its orbit and the furtherest point.
Alternatively if you don't desire 'realism' in your fantasy world, then you can place your planet in any location in its solar system and with an unlimited number of stars if you so desire. You should still consider the type of influences your suns would have on your planet such as the amount of heat and energy that would be generated and the amount of light it would receive. Your fantasy world may have a way of processing the light and heat, so that its impact is lessoned upon the surface or it could provide a reason your fantasy races live beneath the world's surface.
The sun influences more than just the heat and the light of a planet. Solar events such as plasma bursts could affect communication channels on your fictional world or even the use of 'magic'. The sun's basic influence might extend to the culture of a world and the type of life forms that exist, the weather and it interacts with the chemical and mineral compositions of a planet including water. Ancient civilizations such as Ancient Greece and the Mayans worshiped a solar deity and this is reflected in many other cultures. Solar eclipses in many cultures have "foretold" great events including great disasters.
In the Night Sky
Nighttime on a rotating and orbiting planet like Earth occurs on the part of the planet that faces away from the sun. If your fantasy solar system lies in a binary system, night time may not be a regular feature for your world. A world in a system with more than one sun may not always experience a dark night if both suns are in close proximity to your world. A multi star system may also have a less regular day - night - day - night pattern to the amount of light that arrives upon the surface. It will all depend on the orbit of your world and its distance to the suns in its solar system.
Other planets or terrestrial objects of significant size that lie close to your fantasy world could also be the reason for causing night time by blocking out the sun's light. This can be seen in the relationship between the Earth and the moon, where the various phases of the moon, are created by the Earth's shadow being cast across the face of the moon as it passes between the moon and the sun. If your world was the Earth's moon, then your people might experience night time when the Earth's shadow falls across the moon's surface as it passes between the Sun and the moon.
The moon is more than just a pretty object in the sky. The moon's gravitational force combined with the sun effects the movement of our oceans, seas and to a small extent, large lakes. Significant bodies of water, bulge in the direction of the moon, pulled by its gravitational force. How do moons interact with your fantasy world? Are they responsible for the rise and fall of the oceans? How many moons does your fantasy world have?
One of the most popular scientific theories hypothesize (Giant Impact Hypothesis) that the moon was once a large asteroid or planet that collided with the earth. The moon is currently pulling away from the Earth and out of the Earth's gravitational pull. If a similar impact occurred with your fantasy planet what influences could it the collision have had? Could the two bodies have shared atmospheres and exchanged material? Perhaps even the first elements of life as is speculated by some schools of thought about Earth?
Another consideration when looking developing your own star maps for your fantasy world is the number of planets that exist in your solar system, the location of those planets and proximity to your world, whether life exists on those planets and what type of interaction those planets have with your own fantasy world.
Constellations have not just been used for predicting the future or characteristics about a person based on their birth and the alignment of planets. Constellations have been quite handy for developing religions in many societies and are still used as a navigational tool for seaman and other adventurers.
The night sky has many fascinating elements that you could utilize in your fantasy world and as part of your science fiction and fantasy writing. Passing asteroids, black holes, shooting stars, comets and UFO's are fascinating things to have interacting with your fantasy planet. Of course you could come up with your own fantasy stellar object like a plasma star bridge that joins your fantasy world to your moons or other dimensions.
If you are developing your fictional world for a fantasy story, using the information about your solar system in your story can be challenging particularly if the interaction of stellar objects is subtle and not weaved into the storytelling as a main or secondry theme.
Navigational star charts might be useful to create if you have a seafaring or other travelling or nomadic characters. Desert cultures might also use the stars to navigate across the expanse of ever changing sea dunes. If you have characters who are involved in religions and other types of cults then they may be influenced by astral events and could discover meaning, purpose and symbolism through happenings they see and experience in the sky.
If you are a fictional world builder or geofictionalist than you may want to dig deeper into the external influences of your fantasy world. Learning how Earth is influenced by external factors will provide you with a good foundation on how to approach and apply the external influences to your fantasy world and it will also help to foster your imagination.