The size of space

August 19, 2006

I'm reading Bill Bryson's A Short History of Nearly Everything. It's been on my bookshelf for a while but I've finally gotten around to it. I've just read the chapter on the solar system, and quite frankly, it's mind-blowing. I am pretty ignorant regarding astronomy, but it seems to me that I should know a lot more than I do about our little planet and its place in the universe. Anyway, this little section on relative scale was pretty interesting:

On a diagram of the solar system to scale, with the Earth reduced to about the diameter of a pea, Jupiter would be over 300 metres away and Pluto would be two and a half kilometres distant (and about the size of a bacterium, so you wouldn't be able to see it anyway). On the same scale, Proxima Centauri, our nearest star, would be 16,000 kilometres away. Even if you shrank down everything so that Jupiter was as small as the full stop at the end of this sentence, and Pluto was no bigger than a molecule, Pluto would still be over 10 metres away.

Kind of makes you appreciate how inaccurate those solar system diagrams you saw at school really were, doesn't it?

It got me thinking - instead of reducing Earth to the size of a pea, how about you expand a pea to the size of Earth - how big would the elements of the solar system be in that scale?

Well... fear not because I've done the maths for you. If a pea were the size of Earth, then in that scale, Mercury could be represented by a Grape Nutâ„¢ - if you don't know what Grape Nuts are, you need to investigate the cereal aisle at your local supermarket; a cricket ball would be about the size of Jupiter; and one of those weird exercise balls you see at gyms would be the same size as the sun.

But get this - and remember our scale of a pea representing Earth - the Milky Way would be 1/10th the diameter of our solar system*. I have to use a distance in space as the equivalent because there's simply nothing else big enough. So that makes our galaxy... quite big.

*This is using the distance of Pluto from the sun as the diameter - actually the solar system is even bigger than this if you go out as far as the Oort cloud or beyond.


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