How to make a scale model of the Solar System

Almost every picture of the Solar System is a fib. The planets sit close together in neat, colourful rows, and the Sun is a bright disc not far away. The truth is emptier and stranger: space is almost all gaps. The best way to feel this is to build a model where both sizes and distances use one scale. This guide shows how to do it with the Sun as a 10 cm ball, gives the numbers worked out from NASA's fact sheets, and explains how to talk about the places where every picture, including ours, has to compromise.

Why a true-scale model is worth the effort

A diagram can teach order, names and relative sizes. It cannot teach emptiness, because there is no room on a page. Only a model that stretches out across a field or a street can show it. Children of 10 to 14 are old enough to calculate the scale themselves, which turns a model into an exercise in ratio, units and measurement. It also builds a useful habit: asking of any diagram, "what is to scale here, and what is not?"

Choose a scale

The method is the same whatever scale you pick: choose one object, fix its size, and multiply everything else by the same factor. Let the Sun be a 10 cm ball, which is easy to find or make. Ten centimetres is 100 millimetres.

NASA's Sun Fact Sheet gives the Sun's volumetric mean radius as 695,700 km, so its diameter is 2 x 695,700 = 1,391,400 km. The scale factor is therefore 100 mm for 1,391,400 km. Divide: 1 mm in the model stands for about 13,914 km in space.

Sizes

Take each planet's diameter from the NASA Planetary Fact Sheet and divide by 13,914 to get millimetres.

Earth, 12,756 km, becomes about 0.92 mm: a grain of sand or a very small seed.
Jupiter, 142,984 km, becomes about 10.3 mm: a pea or a small bead.
Mercury, 4,879 km, becomes 0.35 mm, and Mars, 6,792 km, becomes 0.49 mm.

Even the largest planet is a tenth of the width of the Sun. Children can lay out the objects on a table and see how large the Sun is compared with everything else.

Distances

Now do the same for distances, using the NASA figures for the average distance from the Sun, in millions of km, and converting to metres in the model.

Planet	Distance from Sun (million km)	Model diameter	Model distance
Mercury	57.9	0.35 mm	4.2 m
Venus	108.2	0.87 mm	7.8 m
Earth	149.6	0.92 mm	10.8 m
Mars	228.0	0.49 mm	16.4 m
Jupiter	778.5	10.3 mm	56 m
Saturn	1,432	8.7 mm	103 m
Uranus	2,867	3.7 mm	206 m
Neptune	4,515	3.6 mm	324 m

The calculation for Earth, step by step: 149.6 million km is 149,600,000 km. Divide by 13,914 km per mm to get about 10,752 mm, which is 10.75 m. Do the same for Neptune: 4,515,000,000 / 13,914 is about 324,500 mm, or 324.5 m.

Notice what you now have. The four inner planets all fit within 17 m, the length of a large classroom and corridor. Then there is a huge gap before Jupiter. Neptune is about 324 m from the Sun, roughly three football pitches away. And this is only our own neighbourhood: the nearest other star is too far away to fit on any field, or in any country, at this scale.

Laying out the model

Find a long, straight, safe stretch: a school field, a park path or a quiet street. Mark each distance with a stake, a chalk line or a flag, and place the model planet there. Measure with a long tape, a trundle wheel or paced steps. An average child's step may be around 60 cm, which you can calibrate by walking a measured 10 m and counting, so that 10.75 m is about 18 steps.

Do the walk. At a comfortable pace of roughly 1.3 metres per second, which is an assumption you can time yourself, it takes about 250 seconds, or four minutes, to walk from the Sun to Neptune. Ask the group to guess beforehand. Nearly everyone guesses too few steps. The Moon, incidentally, is 384,000 km from Earth, so on the same scale it sits only 2.8 cm from the Earth, which is a distance you can show with a ruler.

Check with light

For older learners, tie the model to something they can compute. Light travels at about 299,792 km per second. Earth is 149.6 million km from the Sun, so sunlight takes 149,600,000 / 299,792, about 499 seconds, or 8.3 minutes, to reach us. For Neptune, the same calculation gives 4,515,000,000 / 299,792, about 15,060 seconds, or 4.2 hours. Compare it with the four minutes it takes to walk the model: the model's walking time and the real light travel time are different quantities, and mixing them up is a good discussion point.

What the model still gets wrong

A model that is honest about its limits teaches more than one that is not. Use these as discussion points.

Orbits are not circles. NASA lists Earth's closest point to the Sun as 147.1 million km and the furthest as 152.1 million km. The 5.0 million km difference is about 0.36 m in the model, so Earth's position shifts by that much over a year. Our straight line shows only an average.
Planets are not in a line. They are at different points in their orbits at any time. A straight row is a convenience.
Two sizes of "diameter". Planets are slightly flattened by their spin, so the diameter at the equator is bigger than from pole to pole. Say which value you used. We took NASA's listed diameters.
Not everything is a planet. The Solar System has dwarf planets, moons, asteroids and comets as well.

What counts as a planet

The International Astronomical Union agreed in 2006 on what a planet is. According to NASA's summary, it must orbit a star, in our case the Sun, be big enough for its own gravity to pull it into a round shape, and be big enough that its gravity has cleared away other objects of similar size near its orbit. Pluto, with 2,376 km diameter in the NASA table, meets the first two but not the third, so it is classed as a dwarf planet. The model is a good place to put Pluto: at 5,906 million km, it would sit about 425 m from the Sun, a speck of 0.17 mm.

Tool that fits

The Solar System Field Guide (EUR 15, paid once) is a set of 10 coordinated astronomy charts for learners of about 10 to 14: the layers of the Sun, planet sizes, the order of the planets, distances, inner orbits, speed, the Moon, eclipses, a comparison table, and a scale model with the Sun as a 10 cm ball. Every chart states what is to scale and what is not, in a badge and a footer note, and facts follow NASA planetary fact sheets and IAU definitions with a source register. You get 10 A4 and 10 US Letter PDFs, 10 PNG images (3508 x 2480 px), 10 editable SVG files and an 8-page educator guide with an answer key. All artwork is drawn in code; there are no NASA images.

What to do next

The Solar System Field Guide has 10 astronomy charts, from the Sun to a scale model with the Sun as a 10 cm ball, each stating what is to scale, with NASA-based facts, a source register and an 8-page educator guide. €15 once; digital download only.

See the Field Guide

Questions people ask

Are the planets in textbook pictures to scale?

Almost never, and not in distance. If the Sun were a 10 cm ball, Earth would be a speck under a millimetre wide about 10.8 metres away, so a picture that shows them side by side must change one scale or the other. Good diagrams say which quantities are to scale and which are not.

Why is Pluto not called a planet?

In 2006 the International Astronomical Union agreed a definition: a planet orbits the Sun, is massive enough for gravity to pull it into a round shape, and has cleared the neighbourhood around its orbit of other objects of similar size. Pluto meets the first two conditions but not the third, so it is classed as a dwarf planet.

Why do the distances in tables vary between sources?

Orbits are ellipses, so the distance from the Sun changes through the year. NASA's fact sheet lists the average distance, as well as the nearest and furthest points. Sources also differ on whether they quote equatorial or mean diameters, so always note which one you used.

Sources

We checked each source on 17 October 2026. If a fact here is out of date, tell us at hello@hiddenway.info.