Armillary sphere (geocentric)

Description

A horizon ring is attached to a stand with three arms on a square base. Within it a movable meridian ring which bears the sphere is fixed on the vertical axis; its diameter is the axis of the ecliptic with the wooden globe of the earth in the middle. A band of brass engraved with the signs of the zodiac, the equator ring, the two tropics and the polar circles, as well as the poles, both real and magnetic, together with two of the seven planets then known (probably sun and moon) complete the armillary sphere. It is a late example of the 'Ptolomaic' geocentric view of the universe challenged by Copernicus but favoured by astrologers up until the C18. Such spherical models of the heavens had been used for astronomical calculations since antiquity. In this case the representation of the paths of the planets with rings of brass wire ('armillae') had the advantage of transparency, by contrast to solid celestial globes.