In astronomy, as in all the sciences founded on the Galilean method, the fundamental concepts at the basis of a theory are often represented using models. This makes it easier to understand and study the phenomena, and in some cases, even makes it possible to foresee new properties. While celestial and terrestrial globes are especially appreciated for their beauty in representing the universe, three-dimensional models, often with mechanical motion, are used to better understand the theories hypothesized. The planetary machine, which was operated by a small crank, provided a material view of the Copernican theory, with the Earth in orbit around the sun. Today models used to represent the theories are primarily virtual scenarios built upon the enormous calculating power of computers.