Armillary sphere

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 armillary sphere (so named because of the metal rings called armilla, like the armbands of ancient Rome) represented the universe according to the Ptolemaic view that the Earth is at the center.