The Mathematical Tourist Visits Tycho
Brahe on the Island of Ven and in Prague
1.) The planets move round the Sun in ellipses; the Sun is at one focus of these ellipses. 2.) The line joining the Sun and a planet sweeps out equal areas in equal times. 3.) The square of the time for one complete revolution of each planet is proportional to the cube of its mean distance from the Sun. 
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we highly recommend the Wikipedia article and its extensive list of references, The NCB thanks Det Kongelige Bibliotek in Copenhagen. The NCB also thanks Nicholas Mew, CSULA '07, for the Flash code that we are still using in 2012. 

