# Practical Exercise 4: Scales of planet sizes in the Solar System

As in the previous activity we will be creating a model, this time a model of planets in the Solar System. The task is to find the diameters or radii of the planets and calculate how many times the other planets are larger or smaller than the Earth:

 Planet Diameter (km) Scale Mercury 4,880 0.40 Venus 12,103 0.95 The Earth 12,756 1.00 Mars 6,794 0.53 Jupiter 142,984 11.23 Saturn 120,536 9.46 Urán 51,118 4.06 Neptún 49,532 3.88

In lower classes it is not a problem to draw the planets at this scale or model them from colourful plasticine. In connection with Activity 2, it is possible to prepare a planetary path, e.g. on the school corridor. In this case, however, it is necessary to emphasize that the scale of the planet sizes is different from the scale of distances - if we chose the scale of 1 au = 1 metre, the diameter of Jupiter in this model would be less than one millimetre!

After completing these activities, pupils should be able to say that:
• we use kilometres e.g. to measure distances between planets and their moons,

• astronomical units are used to measure distances between planets or between a central star and planets in planetary systems,
• light years e.g. to measure distances between stars,
• parsecs to measure distances between galaxies.