The Vast Emptiness of the Solar System

One of the hardest things to comprehend about the universe is its scale.

Nothing about it is ‘human sized’ and even the English language falls short when trying to describe just how enormous, vast, and immense the universe is.

Instead us astronomers revert to astro-speak and refer to distances in terms of light years, parsecs, or even redshifts. These units keep the numbers smaller, but they don’t do much to convey size in ways that the human brain can comprehend.

Scale of the Solar System

Even our own Solar System is huge – and mostly empty space. Most ‘pictures’ of the Solar System look something like the top image to the left – the Sun and eight planets crammed together into one shot. But in reality, the Solar System looks nothing like this. The Sun is far too small compared to the planets, and the distances between the planets are far too short.

Other images show the true size of the Sun and the planets, but ignore distances, such as the second one to the left. These are great for showing just how gigantic the Sun and the gas giants are compared to the inner rocky planets of Mercury, Venus, Earth, and Mars. But you get the sense that they’re all near neighbours.

Still other images show the distances between planets to scale, but ignore the size, such as the third image to the left.

But try to represent both size of the planets and the distance, and you have to revert to incredibly long, huge images, or else use the infinite power of the webpage to scroll endlessly through the Solar System (see here or here).

These websites are great if you have plenty of spare time to scroll through webpage, and they’re certainly memorable, but here at the National Space Centre we like the idea of getting people outside and encouraging them to physically experience the vastness of the Solar System by walking, cycling, or running their way through the Solar System.

Here in Leicester we don’t have a permanent Solar System trail of the likes of York or Melbourne (yet!). But thanks to a free app from the British Science Association, you can now travel through the Solar System, wherever you are, just as long as GPS satellites can find your phone.

Run the Solar System

The Run the Solar System app shrinks the Solar System to the size of just 10 kilometres between the Sun and Neptune (instead of the whopping 4.5 billion kilometres that really lie between them!). On this scale, the Sun is just 3 metres across (instead of 1.39 million kilometres!), and all the sizes become much more comprehensible.

But what really becomes apparent is just how much empty space there is in the Solar System. The intrepid walker, cyclist, or runner starts their journey at the Sun and heads off, guided by audio commentary from BBC presenter and science writer Dallas Campbell.

Just 130 metres in and tiny, cratered Mercury appears. It’s the closest planet to the Sun, but somewhat counterintuitively, not the hottest planet. That honour belongs to the next planet, Venus, only 240 metres from the start. Earth (330 metres) and Mars (510 metres) follow in quick succession, but then the emptiness of the Solar System really starts to become apparent.

Jupiter doesn’t appear for another 1.22 kilometres after Mars on this scale, and Saturn is similarly distant from Jupiter.

But the real shockers are Uranus and Neptune, and just how far they away they are. In the app, you have a long radio silence of 3.21 kilometres between Saturn and Uranus (in reality it’s 1.44 billion kilometres!). But even when you get to Uranus, the next-to-last planet, you’ve only travelled 6.39 kilometres and you have to go another 3.61 kilometres to reach Neptune, the final planet in the Solar System.

(The app tactfully mentions Pluto being further out, but since it’s no longer an official planet, the app ends at Neptune).

That’s a lot of empty space to ponder the big cosmic questions – even when you shrink the Solar System to just 10 kilometres.

Give it a try!

Apps and trails like this do a great job of illustrating the vastness of space, in a quirky, memorable way. As an added bonus, you get to learn a few fun facts about each planet along the route.

While it’s British Science Week, the National Space Centre is encouraging everyone to try out the free app. If you’re local to Leicester, check out our suggested, traffic-free route from the Space Centre to Victoria Park and back, but the beauty of the app is that you can run it from anywhere.

Do have a go and let us know how you get on! There’s even a chance to win a free ticket to visit the National Space Centre.

More details and links to the app are on our Facebook event page.