Kepler

the great astronomer, was bom in 1571, and was invited to Prague by Tycho Brahe (q.v.) in 1599 to help in preparing the Rodolphin astronomical tables. Brahe died in 1601, and Kepler continued the work alone, publishing the tables eventually in 1627. It was partly the po e ion of Brahe’s papers and precise observations that enabled Kepler to establish his three great laws, from which Newton determined the laws of the attraction of gravitation. K.’s three laws are—(1) Every planet describes an ellipse. (2) The line joining the centre of the sun with the centre of each planet pa es over equal areas in equal times. The squares of the periods taken by two planets for complete revolution round the sun are proportional to the cubes of their mean