The Cometarium is, by analogy with the planetarium, a mechanical device to illustrate the path of a comet. This example, from the Smithsonian Insititution, traces out the path of Halley's Comet of 1682, which was studied by Edmund Halley (1656-1742) who was a professor at Oxford and later the Astronomer-Royal of England. The sun is shown at one focal point of the earth's elliptical orbit, which seems to be far too eccentric. Turning the crank makes the comet and the earth go around.
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