Number of words: 440

For discussion of the motivations which impel one to pursue the goals of science, no example is better than that of Johannes Kepler. Kepler’s uniqueness derives from the position he singly occupies at the great crossroads where science shed its enveloping dogmas and the pathway was prepared for Newton. Kepler, in his inquiries, asked questions that none before him, including Copernicus, had asked. Kepler’s laws differ qualitatively from earlier assumptions about planetary orbits: the assertion that planetary orbits ‘are ellipses’ in no way resembles the kind of improvements that his predecessors had sought. In his analysis of the motions of the planets, Kepler was not preoccupied with geometrical questions; he asked, instead, questions such as ‘what is the origin of planetary motions?’, ‘If the sun is at the centre of the solar system, as it is in the Copernican scheme, should not that fact be discernible in the motions and in the orbits of the planets themselves?’. These are questions in physics; not in some preconceived geometrical framework.

While Kepler’s approach to the problem of planetary motions was radically different from that of anyone before him, his work is pre- eminent for the manner in which he extracted general laws from a careful examination of the observations. His examination was long and it was arduous: it took him twenty and more years of constant and persistent effort; but he never lost sight of his goal. For him, it was a search for the Holy Grail in a very literal sense.

Before I describe the manner of Kepler’s search, I should like to say that I am in no sense a scholar of medieval astronomy. My knowledge of Kepler is in fact mostly derived from Arthur Koestler’s The Sleep-walkers: A History of Man’s Changing Vision of the Universe, some collateral reading, and some discussions with scholars who know very much more. Koestler’s sensitive account of Kepler, his life and his achievements, includes numerous quotations from Kepler’s own writings. My remarks are largely based on these quotations.

 From the outset Kepler realized that a careful study of the orbit of Mars will provide the key to planetary motions because its orbit departs from a circle the most; and it had defeated Copernicus; and further that an analysis of the accurate observations of Tycho Brahe was an essential prerequisite. As Kepler wrote:

Let all keep silence and hark to Tycho who has devoted thirty-five years to his observations. For Tycho alone do I wait; he shall explain to me the order and arrangement of the orbits…..

Excerpted from page 5 – 6  of  S. Chandrasekhar ‘Man of Science ’ by A.P.J. Abdul Kalam