| In modern terms, the three laws developed by Johann Kepler
(1571-1630) to describe planetary motion around the sun are:
1. The planets move in ellipses with the sun at the shared focus.
2. The line joining the sun and a planet sweeps out equal areas in equal times.
3. The square of the time of revolution of each planet is proportional to the cube of its mean distance from the sun.
This model from Transylvania University allows the first and second laws to be simulated. I suspect that it is from the second half of the nineteenth century; its maker is unknown.
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