An Orrery (sometimes referred to as a Planetarium) is a model of our solar system, showing the sun at the center and the Earth and other planets orbiting it. Orreries range in size from small hand-held devices to table-sized models over a meter wide.
While not used for navigation, orreries are still an important benchmark in the history of science: they mark the widespread acceptance of the Sun's presence at the center of the solar system. Many proudly display the gear-work that allows them to be cranked to a particular time, making an analogy with the idea of "God as Clock-maker" that was common at the time.
Devices such as the Antikythera Mechanism were built to show or calculate astronomical information before 100 BCE. The first known clockwork model of the solar system was created by Giovanni Dondi in 1348.
- The Grand Orrery at Harvard's eMuseum site, including a zoomable image.
- A description of planetariums from Museo Galileo.
- Wikipedia's pages on Orreries.
- The Real-time Orrery at the Long Now foundation, which turns at the same rate as our actual solar system.