The armillary sphere is an astronomical instrument applied in navigation that consists of a reduced model of the cosmos . It is estimated that it was developed over time through meticulous observations of the apparent movement of the stars around the Earth.

The large outer ring shows the declination scale of fixed stars on the celestial sphere; the little ball in the center, the Earth. [ 3 ] The sphere is shown through a set of armillas, a word that designates rings, bracelets or hoops and from which the name « armillary » derives . These arms are articulated and indicate the main great circles: the poles , the tropics , the meridians and the equator . To these is added a diagonal band, inclined 23.5º between the tropics showing the path of the Sun in the 365 days of the year, but which is often presented with other inclinations, for purely aesthetic reasons