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UNITED KINGDOM - APRIL 11: This planetary model was designed and made by the Scottish astronomer James Ferguson (1710-1766). Called an orrery, or more correctly a tellurium, it is a demonstration model to show the motions of the Earth and Moon around the Sun. This example is of wood construction with printed-paper scales and labelling. Such devices became popular during the 17th century, especially after Sir Isaac Newton (1642-1727) published his universal theory of gravity in 1687. To reproduce the motions of the solar system, this model uses hand driven pulleys with cords. This type of model would have been commonly employed at public astronomy lectures, such as those widely given by Ferguson during his lifetime. (Photo by SSPL/Getty Images)