Tutorial – How to Build a Solar System

This is a little deviation from my usual project posts. Instead of showing a project I’ve finished I’ll run through a bit of a Tutorial/How to on designing your own Fantasy/Sci-Fi World Solar system. This is the process I used to design the Sarilo system in the previous post. In looking for this kind of information on the WWW, I pretty much came up blank -everything was either very high level or assumed your world was an earth clone except for the continental layout . A word of caution: I’m no expert mathematician or physicists so I may have made some liberal assumptions with some of the formulas and maths below, if your reading this blog post for some sort of school project (unless it’s “Build a Fantasy/Sci-fi Solar system”), turn back now.

Jaw Dropping Picture for your Players

First up you’ll need to design  a Solar System layout, how many planets what types etc. If you’re going to all this trouble at some point your going to want to casually insert some kind of picture into your gaming session so the players can go “coooool”. So behold I have assembled the ultimate in solar system development tools, I’m possible over selling it a little. Below is a link to a very basic drag and drop solar system assembly page best viewed at 1280×1024 (+). It uses only CSS and Javascript to run no fancy flash around here . I checked and it seems to function best in IE7 and 8 (just say yes to allowing active content if your asked). It functions tolerably well in Firefox although changing label names is irritating,  right click them first and then it’ll let you adjust the label name. Go forth and design a Solar System using the below or if your so inclined use Photoshop,  GIMP or something else:

Link to Builder

Link to Builder

Hopefully your back with a semi-pretty Solar system picture to throw at your players. Now we need to flesh out some of the details, how far is each planet from the sun how long does it take to orbit the sun etc. Now if you’ve stuck your habitable planet way out near where Pluto normally sits, now would be a good time to adjust it to somewhere closer to the sun rings 2-4 (possibly 5)are the best places for habitable planets. However it’s your Solar system so feel free to keep it that way but you’ll see the interesting impacts below.

Specify Planet Distance in AU

Don’t get to hung up on how far an AU is.  Just be aware a good range for Terrestrial (Earth like) planets is approximately 0.8 AU’s to 2 AU’s. Earth in our Solar System sits at 1 AU from the sun, Pluto hangs way out at 39 AU and Mercury at a toasty .4 AU’s. Now Assign each planet an AU Distance from the Solar System Star. The planets don’t have to be as spread out as much as our Solar System but do be aware big planets to close to each other could in reality have interesting effects on each others orbits, Feel free to play around with this Solar System builder. I punched in an approximation of the Sarilo System and ran it for a 100000 years (about 4-5 days) with no problem.  It’s interesting to try to create a stable solar system with one planet on an elliptical orbit that doesn’t wipe out your other planets, I have no idea why a comet hasn’t run into Earth yet .

A little bit of Math

This bit is fairly glossed over, if you want to get into the full workings and understanding feel free to check out  Keplers Laws, for me I’m happy with the below. Basically grab your AU distance for your first planet and place it to the power 3/2, basically 1.5 and you’ll get the orbit of your planet in equivalent earth years. An example My primary planet Etena is 1.24 AU from the Star Ravi, 1.24 to the power of 1.5 equals 1.381 earth years or 504 earth days:

To make things super simple here is an Orbit calculator online (right at the very bottom of the page)or use this spreadsheet I assembled . Using the above does assume certain similarities between our Solar System and the fantasy one but unless you really want to get into some heavy math just live with the above .

A little bit more Maths

So now you’ve got your planets and you know how many earth days it is to year for each planet. You can just see all your NPC’s running complex mathematical conversions every time they try to calculate what season it is. Time to give your planets unique day lengths etc. I’ll admit I stuck with an hour being 60mins for all the calculations I’m just not that dedicated to make up whole new time system. For each of your planets allocate the number of hours in a day, before giving your earth like planet a 500 hour day, think what impacts this would have on your planets society. I’d recommend to keep your earth like planets hours in a day between 20-30 for easier game play.

Once you have the number of hours in day for a planet  simply take your number of earth days in a year x by twenty four then divide by the number of hours in your planets days, this is the number of the planets days in a year, as an example Etena has 504 earth days in an orbit and 26 hours in a day. 504 x 24 = 12096 hours then 12096/26= 465.2. So there are 465 Etena days in a Year. If you like you can do the above calculation for all your planets. My handy spreadsheet will do these calculations for you .

Adding the detail from the above

So you now have a Custom Year Calander for your planet which will if you need it to stand up to at least cursory mathematical checking. But what are some of the impacts gamewise? Below is a bit of dot point list of things to consider:

• If your year is very long (in earth days), the seasons will be longer, more food might need to be stored for winter or a double cropping season might be carried out, plants might mature slower.
• If your year is shorter (in earth days), plants might mature quicker, as winter is shorter less food needs to be stored.
• Longer/Shorter Day length could impact working day length etc (shop opening hours)
• People’s ages will be different younger or older depending on shorter or longer years, maybe you age by each season instead.
• Certain events could be more or less important, ie if spring comes around every 100 days it’s going to seem less important to celebrate, however if winter is 250 days long your definitely going to have a big party when that’s over.  (or if your planets out by Pluto your whole life might be lived in “winter”)
• Is your habitable planet closer or further to the sun, this could make it hotter or colder.

Basically think about how things would impact you if the days and years were of different lengths. Now that you know how many days are in your planets year you can design up a calendar for your players to use. Remember to include seasons, approximately one per each quarter of the year.

Hope this information is useful to other people building up a campaign world.

Orbit Calculator – Spreadsheet

Solar System Builder

World Building – Sarilo Star System Tapestry

I’ve been slowly writing and adding to my campaign world setting, I only really work on this when it’s late at night or if I’m very tired. The latest piece I’ve finished up is a solar system map. I decided to start right from the top and work my way down. So I had a feel for the Planets rotational period and year length etc I worked up a Solar System Map and a few Planetary Statistics:

Above is the Original image I assembled using elements from a few different NASA photos and images that NASA have made freely available. The planets are obviously not spaced out to any kind of scale. I’ve made the Sarilo System a dual Habitable planet system, although to start with I’ll only be detailing the Planet of Etena. Once I had the above created I ran it through a few filters to try and get a tapestry effect:

It’s not perfect but it does give the impression of a tapestry, I should have really added some aging like holes and ragged edges, but as it’s supposed to be a one of kind tapestry made by a famous Astromagus. It should be well looked after and protected so aging didn’t seem very appropriate. I pulled together rough statistics for each planet:

Name	Sihnon	Etena	Ilvaya (ilvaya)	Ceninia	Onayel	Aran	Tevasi
Position	1st Planet	2nd Planet	3rd Planet	4th Planet	5th Planet	6th Planet	7th Planet
Type	Hot Gas Giant	Terrestrial (Life)	Terrestrial (Life)	Frozen/Ice	Gas Giant	Liquid Gas	Barren Rock
Distance from Star	0.41 AU	1.24 AU	1.76 AU	3.2 AU	5.1AU	8.5AU	12 AU
Diameter (KM)
Day Length	7.5 hours	26 hours	27 hours	66 hours	16 hours	13.5 hours	350 hours
Days a Year	304 Sihnon Days	465 Etena Days	757 Hyrokkin Days	759 Ceninia Days	6306 Onayel Days	16081 Aran Days	1040 Tevasi Days
Equiv Earth Days	95	504	852	2090	4204	9045	15173
Moons	0	2	5	1	16	8	0
Rings	0	0	0	0	1	0	0

Assuming I’ve understood it correctly I used Keplers third law to calculate Orbital timeframes and I included an equivalency back to earth days. I realize using Keplers third law wont be a 100% accurate as I’m pretty much assuming that the Sarilo System is then the same as our Solar system but I figure for a Fantasy game setting it should be fine. The other figures are all made up, I’m still working on the Planetary Diameters, need to be a little more careful with those.

As I don’t get to GM very much (or at all any more) and I really enjoy world building I’m just going to do this Campaign world building project as something fun to do when I feel like it. I will continue to add to the world and will make posts here of anything of note. I have begun to upload some of the Info to a wiki but I’m not quiet ready to post the URL as it’s very empty at this stage .

I’ll get back to Mayhem city and Hinterland builds.

(The layout of my image above was based on this one, although mines a very poor imitation . I believe it appeared in or on a magazine cover at some point)

Initial Mapping Finished for D&D Group

Well I’m finding the new projects page very useful, it lets me see what I could be working on and provides motivation to get a project finished so I can cross an item off. Seems the old Psychology of crossing items of lists still works on me. If it helps me finish more things I’m more than happy to use what helps.

These are the initial maps for the world my D&D group will frequent, half the fun for me as a DM is building a world and being able to throw whatever I need into a setting without me feeling like I’m breaking one of the predefined settings.

The World is called Etana and the main continent/island the group/s will start on is Mytivia. For the moment we are running 2 seperate sets of characters a primary set with full storyline and RP elements and a secondary set who are pretty much used for trawling around dungeons and receive double the experience award you normally receive as per 4ed. The Primary set will affect the geopolitical landscape were as the secondary set will be used for off the cuff adventures were I literally just sit with a laptop a pen and a piece of grid paper and make up some dodgy monster bash on the fly .

A little info on the maps, the world map has been done in Winkel Tripel Projection, well as close as I could get doing it by eye in Gimp. Very few details are on the world map at this stage as I want to be able to use player input to add features details and names, it’s their world as well. The smaller continental map of Mytivia itself shows the major cities and main roads.

The Continental map was made using a combination of inkscape and gimp. I had to move the map to gimp as inkscape began to have serious performance issues with the 200-300 mb file. When the map is open in Gimp it is 50cmx30cm @ 300dpi with a rather large number of layers and can take along time to refresh, but I gave the map a lot of space so that I can zoom in and add more details later on. I suspect I may just end up copying segments of the map out however and making more zoomed in local maps in a new Gimp file to help with performance.

All of the icons etc I drew up in inkscape with the exception of the Compass rose which I downloaded from wikimedia commons. Again names of some places etc have been left off so that my players can suggest names and help build the world up and they feel more attached involved with the game world.

I’m fairly happy with the resulting maps, although there no were near as good as what some of the people churn out across at the Cartographers guild. If you want to learn anything about mapping check out their forums.

I’ll post up more detailed/geopolitical information about the world later on as time permits, I have far chunk of info written down and some still in the old brainbox. In the long term I’ll put all the info into a wiki so I can sort the information in a more logical fashion rather than just a pile of loose Blog posts and make it easier on me to reference when DM’ing.

Click the images to load the large version

Etena

Mytivia

I think I might do some miniature painting next