An Eidouranion is a kind of orrery that combined mechanical movement with a method of back projection. Its invention is attributed to Adam Walker who in the 1780s built one measuring 27 feet in diameter. He used it to accompany his lectures on astronomy. It is an ancestor of planetarium projectors.
The word "eidouranion" derives from the Greek compound "eid + ouranos". The combining elements are "eidos", which means "what is seen, shape, form", and "ouranos", which was the name of the god of the heavens. Thus, the combined form means "shaped like the heavens" or "formed like the heavens".
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- King, Henry C, and John R. Millburn. Geared to the Stars: The Evolution of Planetariums, Orreries, and Astronomical Clocks. Toronto: University of Toronto Press, 1978. Print. [esp. Ch. 19: The Eidouranion and Other Large Transparent Orreries]