Size of the Solar System

The first attempt to determine the size of the Solar System was by Ptolemy, who assumed that the Solar System was filled by the epicycles of the planets and there is no empty space in the Universe. From the sizes of the planetary epicycles need to fit the observed planetary orbits, he was able to estimate the size of the Solar System (Sect. 15.1, Vol. 1). In his book Planetary Hypothesis, Ptolemy listed the maximum distance of Saturn from Earth as 19,865 Earth radii, and this was used as the maximum extent of the Solar System. In the heliocentric model, Copernicus was able to determine the relative sizes of the planetary orbits (Sect. 16.2, Vol. 1). Because the physical sizes of the planetary orbits are scaled to the distance between the Earth and the Sun, this distance represents the key parameter for determining the size of the Solar System.