The size of a planet can be determined from its diameter. Diameter, you might remember from maths class, is the distance from one end of circle or sphere to another side, going through the middle.
In this activity, you will make two scale models of the solar system. A scale model uses the same measurement ratios as the real object does. The first model will compare the distance the planets are from the sun in astronomical units, the other model will compare the size of the planets using diameters in kilometers. You probably won’t be able to display either of these models, but you will learn a lot about the real dimensions of space.
How can we make a solar system scale model?
We want out model to reflect the relative distances and sizes of the planets.
- Metre stick (this project is much easier if you use the metric system—besides, scientists always use this system!)
- Big outdoor space, at least 33 meters long. Do your experiment on a day that is not windy.
- Large glass or small bowl
- Black marker
- Optional: Eight friends to hold your planets, or you can set the planets down on the ground after you measure the distance from the Sun.
- Optional: Camera to make a permanent record of your model.
- Trace 9 circles using the bowl as a guide. Because the distance scale model only is concerned about distances between the planets, you can make all the planets the same size.
- Label the circles Sun, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
- Cut the circles out.
- Position yourself as the Sun.
- Give each of your friends a cut-out planet to hold.
- Have your friends position themselves the following distances from you. (Note that some of the measurements are in centimeters rather than meters. A centimeter is 1/100 of a metre, just like a cent is 1/100 of a dollar).
Model Distance from “Sun”
- Metric ruler
- White poster board
- Drafting compass (the kind you draw circles with)
- Permanent Marker
- First, we need to compare the diameter of the Earth to that of the other planets. Remember that diameter is the length of a straight line going through the middle of a circle. The Earth’s diameter is 12,760 km. We can divide the diameter of the Earth into the diameters of all the planets, to get a relative comparison.
Diameter in kilometers
Compared to Earth
Size in cm
- Use the ruler to draw a line for the diameter. Start with drawing the relative diameters of Jupiter, Saturn, Uranus and Neptune.
- Using the compass, draw circles around the diameters.
- Fit in the smaller planets (Earth, Mercury, Venus, and Mars) around where you drew the bigger planets.
- Label the planets, so you don’t forget which is which when you are cutting them out. For tiny planets, you might have to use an abbreviation.
- Cut your planets out.
When you build the scale model of solar system distances, you will undoubtedly notice that some of your friends will be much closer together than others. Some of your friends will have to stand quite close to each other, while others will be far enough away to have a hard time hearing you! When you compare the sizes of the planets, Jupiter and Saturn will seem gigantic compared to the others.
The inner planets of the solar system; Mercury, Venus, Earth and Mars are relatively close to the Sun and each other, while the outer planets are relatively distant from each other and the Sun. The material that makes up the solar system is not distributed evenly. The Sun, Jupiter, Saturn, Uranus and Neptune make up the bulk of the material in the solar system. Our own planet is tiny in comparison!
Do you want to make a scale model of the solar system where BothThe distances and diameters are proportional to reality? This table expresses the diameters in A.U, so the size of the planet is correct proportion to its distance from the sun. Remember we set 1 AU, the distance between the Earth and Sun, as equal to 1 metre.
Diameter in kilometers
In AU (meters)
3.2 x 10-5
8.1 x 10-5
8.5 x 10-5
4.5 x 10-5
9.5 x 10-4
8.0 x 10-4
3.5 x 10-4
3.3 x 10-4
As you can see, all the planets would be too tiny to trace and out using equipment you have at home. What this table does remind you of is that space is, as the name suggests, mostly empty, and even big planets make up a tiny part of our solar system.