Demonstrational armillary spheres were commonly produced in England, France and Europe in the 18th and 19th centuries to show various basic principles of astronomy, and continued to be manufactured in the 20th century. An armillary sphere with the earth at the center is known as Ptolemaic, and an armillary sphere with the sun at the center is known as Copernican. Ptolemy (2nd Century A.D), an Alexandrian astronomer believed that the earth was at the center of the universe. Ptolemaic armillary spheres were produced in Islamist countries, reaching advanced levels as early as the 10th century. Notwithstanding that Ptolemaic armillaries have a globe in the center (rather than the sun), they were created to show modern principles of astronomy including the ecliptic plane of the earth and how that relates to the apparent path of the sun and the visibility of various constellations in the zodiac throughout the year.