Shrink the Solar System
Solar System scale model
Pictures in books squeeze the planets together. Pick a size for the Sun, for Earth or for the whole span out to Neptune, and see how small the planets really are and how far apart you would have to place them.
Scale
1 : 2.78 billion
1 mm stands for 2,783 km
Earth
4.6 mm
a peppercorn
Earth to Sun
54 m
1 min walk
| Object | Model size | About the size of | Distance | On foot |
|---|---|---|---|---|
| Sun | 50 cm | a beach ball | centre | – |
| Mercury | 1.8 mm | a mustard seed | 21 m | – |
| Venus | 4.3 mm | a peppercorn | 39 m | – |
| Earth | 4.6 mm | a peppercorn | 54 m | 1 min walk |
| Mars | 2.4 mm | a mustard seed | 82 m | 1 min walk |
| Jupiter | 5.1 cm | a golf ball | 280 m | 3 min walk |
| Saturn | 4.3 cm | a golf ball | 515 m | 6 min walk |
| Uranus | 1.8 cm | a glass marble | 1 km | 12 min walk |
| Neptune | 1.8 cm | a glass marble | 1.6 km | 19 min walk |
| Pluto | 0.85 mm | a poppy seed | 2.1 km | 25 min walk |
| Moon | 1.2 mm | a poppy seed | 14 cm from Earth | – |
| Proxima Centauri | a dot | – | 14,422 km | – |
Worked out Every length is divided by 2,782,800,000: the Sun's diameter becomes 50 cm. Earth's 12,756 km becomes 4.6 mm; its 149.6 million km from the Sun becomes 54 m. Walking at 5 km/h.
Building a model you can walk
Everything is shrunk by one factor: the size you type divided by the real size. With a 50 cm Sun that factor is about 1 : 2.8 billion, and Earth becomes a 4.6 mm peppercorn 54 metres away. Sizes are NASA's equatorial diameters; distances are each planet's average distance from the Sun.
To set out a real model, put the Sun at one end of a park or street, pace out each distance from the Distance column and mark the planets with something of the matching size. The On foot column assumes an easy 5 km/h. The strip above the table shows why diagrams cheat: at true spacing the four rocky planets crowd into roughly the first twentieth of the way to Neptune.
The planets are never in a straight line, so a model shows the scale of the Solar System rather than where things are today. The last row puts the nearest star on the same scale.
Sources
- Diameters and mean distances from the Sun: NASA Planetary Fact Sheet (David R. Williams, NASA Goddard Space Flight Center).
- The Sun's size (volumetric mean radius 695,700 km): NASA Sun Fact Sheet. The Moon's distance (384,400 km): NASA Moon Fact Sheet.
- Proxima Centauri's distance, 4.24 light-years from its parallax: RECONS, The One Hundred Nearest Star Systems (recons.org, as of 1 January 2012).
Questions and answers
Why are the planets so small in the model?
Because space is mostly empty. Earth is about 109 times narrower than the Sun but sits about 107 Sun-widths away from it, so at any scale where you can see the planets, the distances run to hundreds of metres or kilometres.
What scale fits a school playground?
Choose "Neptune's distance from the Sun" and enter the length you have, say 100 m. Earth then shrinks to a speck under a millimetre wide and even Jupiter is only about 3 mm, so a common approach is two models: one for sizes and one for distances.
Where does Pluto go?
At its average distance, about a third further out than Neptune. Its orbit is stretched, so for part of each circuit it is actually closer to the Sun than Neptune is.
Can I print the plan?
Use Copy model plan to paste the sizes and distances into a document, or download the CSV and open it in a spreadsheet to add your own notes.