What is an armillary sphere?
An armillary sphere is a glabe made of movable, concentric rings that depict such things as horizon, meridian, equator, tropic, and polar circles. The earliest known complete armillary is attributed to the Greeks in the early second century A.D Ptolemy created one to promote his geocentric vision of the cosmos. In 1543, German mathematicion Caspar vogen constructed ptolomy’s theory. In the same year, Copernicus published his revolutionary treatise placing the sun at the center of the solar system. Afterward, Ptolemaic and Copernican spheres were exhibited together to display the differences between the two version of the cosmos.