Solid model of the celestial vault, designed for astronomical and astrological calculations, showing the constellations of the so-called "eighth sphere" (carrying the fixed stars) and the circles that describe it: equator, meridian, Tropic of Cancer, Tropic of Capricorn, polar circles, and ecliptic. Already used by the Chaldeans and Egyptians, the celestial globe, made of stone or metal, gave way to more sophisticated representations of the celestial vault, such as the armillary sphere (as early as the Hellenistic period) and the astrolabe (from the 2nd C. C.E.).