Posted by: jugglinbob | February 20, 2013

“Space is big. Really big. You won’t believe…” – Scale Model of the Universe

I’ve been thinking a lot recently about the size of the universe, about how important I am to it, and how much it cares about my existence.

I keep coming back to a Douglas Adams quote:

“Space is big. Really big. You won’t believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it’s a long way down the road to the chemist’s, but that’s just peanuts to space. “

Modern maps make it fairly clear how small the places we know are compared to the rest of the world. Google Earth easily demonstrates this – all of the places I know well and travel often quickly vanish to just a pixel as one zooms out to show first county, then country, then continent and finally the whole world. I think that most of us are fairly confident in our knowledge of our comparative size to the globe, and some are even aware of the size distortion produced in the Mercator projection where, since we as a country in the UK are fairly near to a pole, are given an unfairly large size due to the way that map is formed.

A Thought Experiment to try at Home…

However, it is harder to come to terms with our size on a cosmological scale. Much harder. We are often tricked into thinking that the solar system has a certain scale by diagrams shown in textbooks and the media, as seen in the video below.

Before you watch it though, please try the following thought experiment for yourself – I promise that it is worth it:

Imagine that the world is a basketball, and so, in this scale, the moon is a tennis ball. How far away should the tennis ball Moon be from the basketball Earth in order for it to truly represent the distance between the Earth and it’s natural satellite in the scale of these objects? A foot? A metre? 10m??

Were you close? Anywhere near at all? Perhaps the preview still gave it away? I have to admit that I wasn’t close – I did think that it would be further away than most of the people shown thought, but I still wasn’t anywhere near!

A True Scale Model of the Universe

We never see scale models of the universe, at best we just see representative sizes without the distances in between. So I thought – “Why not have a go at creating a true scale model of the universe? With both sizes and distances?

Firstly, let’s choose something pretty darn small for the Earth as I’m guessing that these sizes are going to get big pretty quickly. A mustard seed perhaps, which is around 1mm in diameter, (and which just coincidently (ahem…) makes the Maths far simpler…) On this scale what should we use for the moon? Something which is only 0.27mm, so it’s about the thickness of a fishing line, (Ok I know that these lines come in different diameters but there is a 0.27mm line, so work with me here!) And how far away from the Earth mustard seed will this line be?

After watching the video above you may not be surprised to discover that it is 3cm away, but to be honest it did still surprise me. The fact that the moon dominates the night sky and illuminates us so powerfully with its reflected light, and yet is no bigger on this scale to the thickness of some fishing line seen end on seems pretty amazing to me!

Anyhow, lets go back to making the model. The Sun is almost 11cm in diameter, and for our model we can use a large orange. Let’s place it down in an empty park in London and see what happens. The nearest planet to the Sun (Mercury) has to be placed down 4.5m away… and is only about the size of a dust mite!

For Venus we can use another mustard seed (as it is almost the same size as Earth), and this goes a further 4m away from Mercury at 8.5m from the orange Sun.

The Earth “mustard seed” is put down at 11.7m from the Sun “orange”, and a grain of salt sized Mars 6m away from that, which is therefore 17.9m from the Sun. Now we just take a few steps back… and try to find all those planets again.

Hummm… Perhaps we should put down some flags into the grass next to the “planets”, just so that we have a small chance of ever finding the Earth again!

And this is before the distances get really big…

For both Jupiter and Saturn we can use a coffee bean. Although Jupiter is larger in reality, on this scale we can’t notice the difference. The Jupiter bean needs to be placed down at… Go on guess…

Coffee bean by

Coffee bean by

… 61m from the sun! Eek! From here I can hardly see my orange “Sun”! And Saturn… well, that’s placed at a frankly ridiculous 112m from the Sun!

For Uranus we can use an ant (preferably a dead one otherwise we might have some planetary drift…) which is put down at 225m, and Neptune, which is another ant, at – and I really hope that your park is big enough – 353m from the orange that we can no longer see from here…

Ok, so that’s our model of the solar system – Oh hang on! No, it’s not – these are just the major planets. For completeness I should add that Pluto would be almost a kilometre away {EDIT: Apparently my Maths went south here, and it’s more like 470m away (Thank you for the input and correction!)} and smaller than a speck of dust anyhow, but the solar system is still far, far larger than that…

Cosmological Scale

The furthest man-made object from us is Voyager 1, which is now 122 AU (astronomical units) away. That’s 122 times the mean distance from the Earth to the Sun – or 1.4 km even on this tiny scale! Which is perhaps a 15 minute walk away from our London park!

And although the media recently reported that Voyager 1 is on the edge of solar system that’s not quite true…

The planetary solar system is theoretically surrounded by the Oort Cloud, icy rocks which are theorised to lie between the zones 1000 AU away and 100 000 AU away, and are loosely bound to the Sun’s gravitation field. On this scale the Oort cloud ranges from starting just a few minutes’ drive away at 12km, and (wait for it!) the many hours to drive the distance from London to Monaco!

Proxima Centauri (the nearest star to us at a mere 4.24 light years) is 3100km from our park in central London. Cairo perhaps? And at this point remember that everywhere that you know, everyone that you have ever met, everyone that you have ever loved, and indeed as far as you are ever going to go is all on that little mustard seed that we have left and lost in the park in London…

Even using this small scale the distances have become unimaginable and so unworkable as a usable model, but I’ll leave you with this last one. How far to the centre of Milky Way on this scale? That is – the Earth is a mustard seed, whilst the Sun an orange. Go on – it’s the last pop quiz question on this page, honest. Have a go…

Our spiral galaxy.  The milky way

Milky WaY image from

On this scale – the centre of the galaxy is still half-way to Mars. And that is when Mars is at it’s closest to us….

And that’s as far as this model can get us – well ok, far further than it should have been used for. We haven’t even looked at the distances to other galaxies, to the edge of the observable universe, or indeed to the theoretical size of the universe itself. And that’s the problem with trying to create a real scale model for both relative sizes and relative distances of astronomical objects. It is not that the objects sizes themselves are unable to be translated to normal size objects, but that when you do that, that the distances rapidly become absurd on the scale you are using. There’s a lot of space in Space…


The universe is indeed large. Larger than we can ever realistically comprehend without using the abstraction of mathematics, and we are (from the universe’s point of view) practically non-existent.

Tim Minchin said in “Storm” (which I’ve previously posted, so I won’t here):

I am a tiny, insignificant, ignorant bit of carbon.
I have one life, and it is short
And unimportant
But thanks to recent scientific advances
I get to live twice as long as my great great great uncle-es and aunt-es.

Although from the universe’s point of view we are tiny. insignificant, and perhaps ignorant, bits of carbon, this is because the universe is big.

Biggly big.

Bigger than you or I can possibly imagine.

This is what science has taught us….

And that truly is both amazing and enlightening – on any scale. To be able to stand on a single insignificant planet and yet be able deduce the size of the universe is… well, to quote Prof Brian Cox: “Amazing…”

But I’m still going to use my car to get the Chemists down the road. It still seems a pretty long way. Sorry Douglas…



  1. Forget the rest on this planet all you need is love and money!

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