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All measurements in the model are calculated using a simple ratio. If we assume that the "Big Ball" represents the Sun then once we know the actual size of the Sun, the actual size of the "Big Ball" and the actual size of the Earth, we can easily calculate what size the model of the Earth should be.

Here’s how we work out the size of the Earth in the model.


Firstly, we will work with the diameter of each object – that’s all we need to know.


The diameter of the Sun is 1,391,016 kilometres. That’s about 109 times the diameter of the Earth which is 12,756 kilometres.

The diameter of the "Big Ball" is only 9 metres or 9,000 millimetres. 

First we’ll work out the exact size of the Earth compared to the Sun.


This gives an exact ratio between the two diameters of 109.048

Using this ratio the appropriate scale for the Earth should therefore be 9,000 divided by 109.048. The result is in millimetres as the diameter of the "Big Ball" is 9,000 millimetres.

That results in a scale diameter for the Earth of 82.5 millimetres.


That’s about the size of a large orange.


Hold a large orange in your hand and stand close to the Big Ball at Naas, and you’ll get a real appreciation for just how big the Sun is compared to the Earth.

The scale diameters for all of the planets are detailed later.

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