Astronomical Adventures

Solar System Scale Modeler

Scale models of our solar system have always fascinated me. The chief difficulty with these models is reconciling the size of the planets with the far greater distances that separate the planets. This Java applet will serve as an aid for those who are interested in producing scale models of the planets and major moons of the solar system. The Solar System Scale Modeler models the size, mass and orbit of the planets and moons of our solar system. Because Astrodigital is metric-friendly, all numbers are given in metric.

How to Use the Program

The Java applet makes use of two data entry fields. Both fields must contain a valid numeric value in order for the program to run. If you make a mistake entering data, an error message will appear immediately below the "Run Simulation" button.

The first data entry field is prefixed with the label "Enter the number of Kilometers per Millimeter". Use this field to specify how many kilometers should be represented by one millimeter. This number will be used for modeling the diameter of the objects and the size of their orbit.

The second data entry field is prefixed with the label "Enter the number of Million Metric Tons per Gram". Use this field to specify how many "Million Metric Tons" should be represented by one gram. This number will be used for modeling the mass of the objects. Please note that a metric ton is equal to 1,000 kilograms so a "Million Metric Tons" is equal to 1,000,000,000,000 kilograms. Therefore, in the scale model, one gram is used to represent 1,000,000,000,000 kilograms. Please note that the grams/metric tons values used here represent mass and not weight. Whereas mass is how one measures the quantity of "stuff" that makes up an object, weight is a measure of the force of the gravity that is acting on the "stuff."

Once you have entered numbers for both data entry fields, use your mouse to click on the "Run Simulation" button to produce a report of the solar system's planets and moons based on the values you entered. The output will appear in the text box labelled "Scaled Solar System Results." Use your mouse to select (highlight) the entire report and copy it to your clipboard. Once in your clipboard, the report can be pasted into the text or word processor of your choice. This way you can customize the report to meet your own needs.


If you enter a zero for either of the two data input fields, you will obtain a report of the actual, not scaled, values for the solar system objects. Use this information as a supplement to the model you have constructed.

Warning on Numeric Format:

Some numbers may appear in scientific notation format. An example of this is the number 1.675E10 which actually means 1.675 * 1010 which is equal to 16,750,000,000.

Warning on Mass Values:

There are a number of moons for which a mass value is not available. For these moons, all reports will contain a value of "0.0" in the "Mass of Object" column of the report.

A brief description of the "Scaled Solar System Results" report fields

Data Field Name Field Description
Report Title AreaIf the report is of a scaled solar system, then the subtitles "Distance Scale: 1 millimeter = n Kilometers " and "Mass Scale ...: 1 gram = n Metric Tons " will be displayed. If the report is for the actual values, then the subtitle "Actual Values for Solar System Object" will be displayed.
Object NameThe name of the object being scaled.
Object ParentThe name of this object's parent body. Note that the Sun's parent is the Milky Way Galaxy.
Diameter of ObjectThe diameter of the named object. The scale size of the object is given in millimeters. The actual size value is given in kilometers.
Distance of Object from ParentThe mean orbital distance of this object from the center, not the surface, of its parent. The scale size of the orbit is in millimeters. The actual size of the orbit is given in kilometers. This number is equivalent to the semi-major axis of the ellipse that defines the orbit. Note that this field will be 0.0 for the Sun since it is the center of our solar system.
Mass of ObjectThe mass (the quantity of matter) of the object. Please do not confuse mass with weight. The scale mass of the object is given in grams (Note that the scale mass in grams can be converted to a scale weight in ounces by multiplying the grams by a conversion factor of 0.035). The actual mass is given in units of Million Metric Tons where 1 million metric tons = 1,000,000,000,000 kilograms.

Selecting a Scale

The numbers that you select as the two scaling factors will be determined by the type of model that you want to build and how much space you have to work with. For instance, if you want to illustrate the distance between the planets, you should choose a relatively large number for the "Kilometers per Millimeter" data entry field. Alternatively, you may want to illustrate the relative distances of moons from their parent planet, for which you would use a smaller number. Or, you may just want to model the relative sizes of the planets, for which you would use an even smaller number of "Kilometers per Millimeter".

Modeling Mass and Converting Mass to Weight

Modeling the masses of the objects in the solar system has been provided as a way of easily illustrating the different masses of the planets and moons. Rather than just using numbers, you can hand a child objects that have weights representative of the masses of the different bodies of the solar system. As mentioned previously, mass is not the same thing as weight. However, you can easily convert the gram masses given in the report into weights in ounces by multiplying the grams by the value 0.035 (rounded from 0.0352733). You can then use your average scale to identify objects that have the same weight as your scaled solar system object.

Closing Comments

I hope that you find the following Java applet for modeling the scale of the solar system useful. If you have any questions, suggestions or problems using this applet, please send an email to the address listed at the bottom of this page.


Need someone to talk about space to your group? Check out the Chicago Society for Space Studies Speakers Bureau

For space art, astronomy, and digital photography stories, visit the Artsnova Blog

Copyright 1999-2007, Astrodigital, http://www.astrodigital.org. All rights reserved.
To ask questions, report problems or for general inquiries, see Contact