menu 5 Solar System
Erasmus+: Key action 2:Strategic Partnerships in School Education


Create a lunar eclipse model. Use a gymnastic ball with a diameter of about 70 cm as the Sun. First calculate the required body sizes and their distances, then find suitably large spheres for the Earth and the Moon and place them at the correct distances. Remember the correct order of the bodies.

Sun diameter
1 400 000 km
Earth diameter
13 000 km
Moon diameter
3 500 km
distance of the Earth from the Sun
150 000 000 km
distance of the Moon from the Earth
400 000 km

Objective of Practical Exercise:

The aim of this activity is to make pupils aware of the vast vastness of interplanetary space and to be able to imagine the mutual distance of bodies in relation to their dimensions. In all illustrations and models of the solar system or lunar eclipse, the bodies are excessively large and very close to each other, it is more or less impossible to draw a model on a real scale. A walk is a suitable situation for correcting the inappropriate idea of a “tight” solar system.

Methodical notes for the teacher:

• Preparation for this activity can be done in advance at school in class or at home during the preparation for physics. In the part of the answer below, we present the calculated values for the diameter of the ball 70 cm, but it is possible to use another ball. If the difference in size is up to about 10 cm, it is not necessary to recalculate the ratio and size. Nothing will change in illustrating the situation. It is then appropriate to carry out the actual implementation when walking to a playground, in a park or on a meadow.

• Beware of length units. It is not necessary to convert real lengths to metres, but it is necessary to realise that all dimensions in the model must be in the same units and all lengths in a real situation as well. In the sample answer we work in a real situation with kilometres (see assignment) and in the model with metres. However, nothing prevents you from converting everything to metres or, conversely, to kilometres and, in addition, practising conversions of length units.

• The demonstration must be carried out on a flat and free surface so that all bodies are visible to each other (they are not hidden among the trees, etc.). It is advisable to hold small bodies (Earth, Moon) by selected pupils in their hands. When laid on the ground, they disappear and will not be visible at all.

• It is enough to determine the distance between the Earth and the Sun approximately by stepping, it will not change anything by the creation of the idea

• Pay attention to the correct order of bodies, the Earth is between the Sun and the Moon during a lunar eclipse.

• It is not enough to perform the calculations, the numbers themselves will not tell the pupils much. The demonstration must be carried out in reality. Only in this way will pupils get the right idea.

Sample answer

The scale of the model is 0.7 metres to 1,400,000 kilometres, i. e. 0.000 000 5 m/km.

Sun diameter
1 400 000 km 0,7 m
Earth diameter
13 000 km 0,006 5 m = 6,5 mm
Moon diameter
3 500 km 0,001 75 m = 1,75 mm
distance of the Earth from the Sun
150 000 000 km 75 m
distance of the Moon from the Earth
400 000 km 0,2 m

Adaptation guidelines for pupils with SEN

Pupils with disabilities 

For students with learning disabilities, it can be difficult to calculate sizes and distances in a model at a ratio in the range of 6 to 7 orders of magnitude. Then you can proceed step by step as follows: 14 : 7 = 2, i. e. to reduce the size twice, and then a million more times. For some pupils, the idea that we are counting metres and kilometres at once can also be problematic, then it may be appropriate to convert everything to metres, even if this increases the ratio by another 3 orders of magnitude. 

Gifted pupils 

Gifted students can recalculate the model in other proportions. They can put together real situations, other times it is necessary to be satisfied with a thought model. Some possible variants: 

• Design the described situation so that it fits on the table top. 

• Determine the sizes and distances of bodies if the Earth is as big as a soccer ball. 

• Calculate what the sizes and distances of bodies would be if the Sun were like an orange.

Another possibility is to extend the exercise to calculate the sizes and distances of other planets in the solar system.