[Title page of Le journal des scavans, with armillary sphere]

An armillary sphere is a model of the celestial sphere used to demonstrate the motions of the planets around the Sun. It consists of a set of rings representing the celestial equator, the ecliptic and other important circles on the celestial sphere, mounted on an axis. The rings can be rotated to show the positions of the stars and planets at different times and dates. Armillary spheres were used by ancient astronomers to study the movements of the heavens and are still used today as decorative objects or educational tools. Armillary spheres were first developed by ancient Greek astronomers, including Hipparchus and Ptolemy, in the 2nd century BC. They were later used by Chinese, Persian and Islamic astronomers. During the Renaissance, armillary spheres became popular with European scientists and were often incorporated into astronomical instruments and globes. Today, armillary spheres can be found in museums, observatories and private collections around the world. Some modern versions incorporate electronic sensors and motors to automate the movement of the rings.