A Sense of Scale Page 2

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.

In the Oxford Observatory we have a scale model of the Solar System on the wall. This shows the distances of the eight planets from the Sun.

The Sun is the only visible object at this scale, with a diameter of 1.4 mm. Neptune, the furthest planet is 4.5 metre away from the Sun. At this scale the planets are invisibly small. See the table for details.

 Scale Model Solar System Actual (km) Scaled (mm) Object Diameter Distance from Sun Diameter Distance 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
is that the rocky planets are all very close to the Sun and that 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. 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.
As we mentioned in the EBook, you cannot
build such a scale model of the Solar System inside a normal building.

The Solar System extends to the Oort Cloud,
up to about half a light year from the Sun.
In this scale model that is up to 4.7 km.
That is actually the real size of the Solar System at this scale.

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.

 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. Good luck!