layed in his thesis, Kepler was invited by Tycho Brahe to Prague to become his assistant and calculate new orbits for the planets from Tycho's observations. Kepler moved to Prague in 1600. Kepler served as Tycho Brahe's assistant until the Brahe’s death. On the death of Brahe in 1601, Kepler assumed his position as imperial mathematician and court astronomer to Rudolf II, Holy Roman emperor. In 1609 his Astronomia Nova (“New Astronomy”) appeared, which contained his first two laws: planets move in elliptical orbits with the sun as one of the laws, and a planet sweeps out equal areas in equal times. This means that the closer a planet comes to the sun, the more rapidly it moves. Whereas other astronomers still followed the ancient precept that the study of the planets is a problem only in kinematics, Kepler took an openly active approach, introducing physics into the heavens. In 1612 Kepler became mathematician to the states of Upper Austria. Between 1617 and 1621 Kepler published Epitome Astronomiae Copernicanae ("Epitome of Copernican Astronomy"), which became the most influential introduction to heliocentric astronomy; in 1619 he published Harmonice Mundi ("Harmony of the World"), in which he derived the heliocentric distances of the planets and their periods from considerations of musical harmony. In this work we find his third law, relating the periods of the planets to their mean orbital radii. Equally important, it became the first textbook of astronomy to be based on Copernican principles, and for the next three decades it was a major influence in converting many astronomers to Keplerian-Copernicanism.The last major work to appear in Kepler's lifetime was the Tabulae Rudolfinae (“Rudolfine Tables”). The new tables, based on Tycho Brahe's accurate observations, were calculated according to Kepler's elliptical astronomy. The English mathematician Sir Isaac Newton relied heavily on Kepler's theories and...
