books.google.de - Johanne Kepler's "Harmonice mundi" was planned in 1599 as a sequel to the "Mysterium cosmographicum." In 1618 Kepler discovered the third law of planetary motion relating to the periodic times of the planets to their mean distances from the sun - a crowning achievement that enabled him to bring the "Harmonice...http://books.google.de/books/about/The_Harmony_of_the_World.html?hl=de&id=rEkLAAAAIAAJ&q=motion+at+aphelion&utm_source=gb-gplus-shareThe Harmony of the World
