International Society for Science & Religion - Library Project

The Eye of Heaven: Ptolemy, Copernicus, Kepler

by Owen Gingerich

Introductory Essay by William R. Shea

Owen Gingerich has written extensively on the history of astronomy from antiquity to the scientific revolution of the seventeenth century. This book is a collection of twenty-five of his best articles written over a quarter of a century. It begins with a 1964 essay "The computer versus Kepler", in which he shows how an astronomer struggled to establish a theoretical model from the conflicting redundancy of data, and ends with "Kepler, Galilei, and the Harmony of the World", published in 1989, a paper that explores Kepler's more daring attempts to find the underlying harmony of the heavens. The major figures that are considered in these articles include Kepler, Ptolemy, Copernicus, Tycho Brahe, Galileo and Newton.

Kepler shared with Ptolemy and Copernicus a profound sense of order and harmony. This was closely linked to his belief that the world was willed by a divine mind. Repeatedly, he stated that geometry is co-eternal with God and that we share in this knowledge because human beings were created in the image of God. From this principle flowed Kepler's ideas on the cosmic link between man's soul and the geometrical configurations of the planets. It also motivated his indefatigable search for the mathematical harmonies of the universe. Contrasting with this mathematical mysticism, yet growing out of it through the remarkable quality of his genius, was his insistence on physical causes. For Kepler, the physical universe was not only a world of discoverable mathematical harmonies but also a world that could be explained by mechanical causes. The outcome was a mechanization and cleansing of the Copernican system. The new world, set it into motion like clockwork, swept away the vestiges of Ptolemaic astronomy.

It remained for Isaac Newton to banish the last traces of Aristotelian physics and to place the heliocentric system on a consistent physical foundation. Although Newton indirectly owed much to Kepler's insistence on physical causes, he rejected the type of arguments so dear to Kepler's mind, and he tried to withhold credit for his achievements. As a result, Kepler is nowhere mentioned in book one of Newton's Principia. Fortunately, Newton's contemporaries felt differently, and his great work was introduced to the Royal Society as "a mathematical demonstration of the Copernican hypothesis as proposed by Kepler". Perhaps the fairest evaluation of Kepler came from the pen of the astronomer Edmond Halley who, in his review of the Principia, wrote that Newton's first 11 propositions were "found to agree with the phenomenon of the celestial motions, as discovered by the great sagacity and diligence of Kepler".

Several articles in this collection focus on comparatively technical aspects of the transformation of astronomy from the ancient geocentric scheme to Kepler's remolding of the Copernican arrangement. Gingerich demolishes the pervasive myth that multiple epicycles brought astronomy to a crisis state at the time of Copernicus and the common error that the Ptolemaic system was ready to collapse of its own weight.