Planet trail in Bernstein, Burgenland, Austria

Image: public domain

The vast distances and immense sizes of the universe are beyond our senses. We can name them, and measure many of them, but we cannot imagine them. The distances and sizes in our solar system are much smaller, but even here we quickly reach the limits of our imagination.

However, there is a trick: you can imagine the Sun, its planets and the distances between them scaled down. You can even build a model that gives us at least some idea of the scale. Such scale-model solar system walks have been set up in several places around the world.

You or your class could make a model like this, too. Choose a long, quiet road—or better yet, a straight forest path. You’ll need a route that is 2.3 kilometres long. Scale down the Sun, its planets and the distances between them so that two billion kilometres becomes just one metre. The Sun, which is 1.4 million kilometres in diameter, will then be just 70 centimetres across, while the planets and the distances between them will be proportionally smaller.

At the start of the path, make a circle with a diameter of 70 centimetres and fill it with gravel, granules, pine cones or something similar. This will be our Sun. Make the planets from any material you like, such as modelling clay.The Mercury is 55 million kilometres from the Sun and has a diameter of just 4,880 kilometres. Your model Mercury will then be about the size of a grain of rice, measuring 2.4 millimetres. Place this tiny ball 27 metres from your model Sun. 

Venus and the Earth in your model are about the size of peas. The bright evening star has a diameter of just 0.6 centimetres, while our blue planet would shrink to just under 0.65 centimetres. Venus orbits the Sun at a distance of 54 metres, while the distance between Earth and the Sun is 75 metres.

The Mars is slightly larger than Mercury, but at just under 0.4 centimeters in diameter, it is tiny too—especially when you consider that it is 114 meters from the Sun. Jupiter, at 7.2 centimeters, is about the size of a tennis ball. But it is already almost 400 meters from your Sun.

Saturn is only slightly smaller, with a diameter of 6 centimetres. In your model, it will be 688 metres from the Sun.

Uranus is only 2.6 centimeters tall, and Neptune is just under 2.5 centimeters. No wonder it is so cold on these planets: Uranus is almost 1.4 kilometers from your Sun, and Neptune is as far as 2.2 kilometers away.

If you also want to include Pluto, you’ll have to extend the route to almost three kilometers. And if you want to represent the distance to the next star, Alpha Centauri, on the same scale, you’ll have to travel almost halfway around the Earth. The distance between your sun, scaled down to 70 centimeters, and its nearest neighboring star would have to be about 20,000 kilometers. In reality, it’s more than 40 trillion.

By the way, you don’t have to create a planetary trail yourself. There are planetary trails in many places in Europe that show the distances between the planets. Perhaps you can find one near you.