An armillary sphere (variations are known as spherical astrolabe, armilla, or armil) is a model of objects in the sky (in the celestial sphere), consisting of a spherical framework of rings, centered on Earth, that represent lines of celestial longitude and latitude and other astronomically important features such as the ecliptic. In astronomy, the geocentric model (also known as geocentrism, or the Ptolemaic system), is the superseded theory that the Earth is the center of the universe, and that all other objects orbit around it. Ptolemy was an Egyptian polymath, who made studies in astrology, astronomy, geography and mathematics. This woodcut is by Oronce Fine, mathematician and author of the Solaribus Horologiis, and was printed in Johannus de Sacrobosco's Textus de Sphaera in 1538.