## The Solar System

Remember our discussion about the scale of the Solar System? (see our EBook "Solar System").
We noticed how difficult it is to get a true sense of distances as compared to the sizes of Sun, planets and moons, and that it isn’t possible to build a scale model within a normal building that is true to scale in both distance and size.

The picture at left shows the Sun and planets to the same scale as regards size, not their distance. Is it possible to draw a picture of the Solar system where both and size and distance are at the same scale?

In our Observatory we have a wall space of about 5 metre length available to build a scale model of the Solar System. This needs to show at least the distances of the eight planets from the Sun at the true scale.

We calculated that if Neptune would have to fit within the 5 metre, the Sun would have a diameter of 1.4 mm. We used an ordinary pinhead of about that size. We realised that the Sun is the only visible object at this scale, and that Neptune, the furthest planet, is 4.5 metre away from the Sun. See the table below for details.

Scale Model Solar System
Actual (km)Scaled (mm)
ObjectDiameterDistance
from Sun
DiameterDistance
from Sun
Sun 1,392,000 - 1.4 -
Mercury 4,853 57,950,000 0.005 58
Venus 12,132 108,110,000 0.012 108
Earth 12,771 149,570,000 0.013 150
Mars 6,768 227,840,000 0.007 228
Jupiter 143,031 778,140,000 0.14 778
Saturn 120,683 1,427,000,000 0.12 1,427
Uranus 51,083 2,870,300,000 0.051 2,870
Neptune 49,550 4,499,900,000 0.050 4,500

What we have learned from this scale model?

The first four rocky planets are all very close to the Sun and the gas planets are, relatively speaking, very far away. Especially Uranus and Neptune are at a lonely distance.

The other thing that we have learned is that the planets are unimaginably small in comparison to their mutual distance. They are mere specks of dust at this scale. Just look at Neptune, a speck of only 0.05 mm orbiting a pinhead of 1.4 mm at a distance of 4.5 metre.

Hence the Solar System is a very empty place, in contrast to what is suggested on many diagrams of the Solar System.
The difficulty is to draw both distance and size to a scale so that you can see something.
You cannot build such a scale model of the Solar System inside a normal building.

The other thing we must realise is that the planets are never lined up all in a straght line away from the Sun. In reality each planet could be anywhere in the plane of the Solar System (the ecliptic). So in this scale model we have invisibly small planets that could be anywhere in a circle at the given distance from the pinhead. This really hits it home that the Solar System is a very empty place, and that pictures such as the one above are very unrealistic. In this picture Neptune would have to be at a distance of more than 400 metres from the Sun.

Actually, the Solar System extends all the way to the Oort Cloud, which is up to about half a light year from the Sun. In this scale model that is 4.7 km. So that is the real size of the Solar System at this scale, in which the Sun is the size of a pinhead.

Above we show another scale model that fits within the text area of this page. The Sun and planets are now even much smaller than in the previous model (see the details in the diagram). Even the Sun cannot be made visible at this scale,
but you can appreciate the true relative distances here.

In this EBook we are going to use this scale model in which our Sun is the size of a pinhead of 1.4 mm.
We will see how this scale model increases in size when we are leaving our Solar System, on a trip to the far reaches of the observable Universe.

## Make your own scale model of the Solar System

Maybe you have space in a hall or corridor that is much longer than the 4.5 metres we use.
Can you double that, or even more?

Alternatively, you can decide that Mercury must be e.g. 1 mm in diameter. Then calculate all the other dimensions of your scale model and see if you can fit it inside somewhere (or not). At least you will get a good idea about the true scale of the Solar System.

Use the values for size and distance in the table above.

Good luck!

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