KEPLER, JOHANNES

born Dec. 27, 1571, Weil der Stadt, Wrttemberg died Nov. 15, 1630, Regensburg Johannes Kepler, oil painting by an unknown artist, 1627. In the cathedral, Strasbourg, France. German astronomer who discovered three major laws of planetary motion, conventionally designated as follows: (1) the planets move in elliptical orbits with the Sun at one focus; (2) the time necessary to traverse any arc of a planetary orbit is proportional to the area of the sector between the central body and that arc (the area law); and (3) there is an exact relationship between the squares of the planets' periodic times and the cubes of the radii of their orbits (the harmonic law). Kepler himself did not call these discoveries laws, as would become customary after Isaac Newton derived them from a new and quite different set of general physical principles. He regarded them as celestial harmonies that reflected God's design for the universe. Kepler's discoveries turned Nicolaus Copernicus' Sun-centred system into a dynamic universe, with the Sun actively pushing the planets around in noncircular orbits. And it was Kepler's notion of a physical astronomy that fixed a new problematic for other important 17th-century world-system builders, the most famous of whom was Newton. Among Kepler's many other achievements, he provided a new and correct account of how vision occurs; he developed a novel explanation for the behaviour of light in the newly invented telescope; he discovered several new, semiregular polyhedrons; and he offered a new theoretical foundation for astrology while at the same time restricting the domain in which its predictions could be considered reliable. A list of his discoveries, however, fails to convey the fact that they constituted for Kepler part of a common edifice of knowledge. The matrix of theological, astrological, and physical ideas from which Kepler's scientific achievements emerged is unusual and fascinating in its own right. Yet, because of the highly original nature of Kepler's discoveries, it requires an act of intellectual empathy for moderns to understand how such lasting results could have evolved from such an apparently unlikely complex of ideas. Although Kepler's scientific work was centred first and foremost on astronomy, that subject as then understoodthe study of the motions of the heavenly bodieswas classified as part of a wider subject of investigation called the science of the stars. The science of the stars was regarded as a mixed science consisting of a mathematical and a physical component and bearing a kinship to other like disciplines, such as music (the study of ratios of tones) and optics (the study of light). It also was subdivided into theoretical and practical categories. Besides the theory of heavenly motions, one had the practical construction of planetary tables and instruments; similarly, the theoretical principles of astrology had a corresponding practical part that dealt with the making of annual astrological forecasts about individuals, cities, the human body, and the weather. Within this framework, Kepler made astronomy an integral part of natural philosophy, but he did so in an unprecedented wayin the process, making unique contributions to astronomy as well as to all its auxiliary disciplines. born , Dec. 27, 1571, Weil der Stadt, Wrttemberg died Nov. 15, 1630, Regensburg German astronomer who discovered that the Earth and planets travel about the Sun in elliptical orbits. He transformed the old, geometric description of the heavens into dynamical astronomy. After studying astronomy at the University of Tbingen under Michael Mstlin, who believed in the Copernican theory, Kepler wrote a paper that came to the attention of Galileo and Tycho Brahe. Subsequently, while lecturing on mathematics, rhetoric, and Virgil at the Lutheran high school in Graz, Austria, Kepler was invited to join Tycho's research staff at the observatory outside Prague. In the following year (1601) Tycho died and Kepler was appointed his successor as imperial mathematician of the Holy Roman Empire. Using Tycho's extraordinarily accurate collection of astronomical observations, Kepler was able to deduce three fundamental laws of planetary motion that later enabled Sir Isaac Newton to formulate his theory of gravitational force. Kepler also founded modern optics by postulating the ray theory of light to explain vision. In 1627 Kepler published his Tabulae Rudolphinae, containing tables that held their place for more than a century, being universally used in calculating planetary positions; tables of refraction and of logarithms; and an extended catalog of 1,005 stars based on Tycho's observations of 777 star positions. Additional reading Kepler's complete works are available in Gesammelte Werke, ed. by Walther von Dyck et al. (1937 ), in the original Latin and German, and in Joannis Kepleri Astronomi Opera Omnia, ed. by Ch. Frisch, 8 vol. (185871), in Latin, an important collection with a 361-page Latin biography that is still a major source for the witchcraft trial. Selections of Kepler's writings in English include Epitome of Copernican Astronomy: IV and V, and The Harmonies of the World: V, both in Mortimer J. Adler (ed.), Great Books of the Western World, 2nd ed., vol. 15 (1990), pp. 8411085, with a biographical note; Johannes Kepler: Life and Letters, ed. and trans. by Carola Baumgardt (1951), a selection of his letters with an introduction by Albert Einstein on his scientific achievements; The Six-Cornered Snowflake (1966), with parallel Latin and English texts; The Secret of the Universe (1981), also including parallel Latin and English texts; and Johannes Kepler: New Astronomy, trans. and ed. by William H. Donahue (1991). Max Caspar (ed.), Bibliographia Kepleriana, 2nd ed. edited by Martha List (1968), in German, is an extensive bibliography.Excellent appreciations, for general readers, of Kepler's life and achievements are Owen Gingerich, Kepler, in Charles Coulston Gillispie (ed.), Dictionary of Scientific Biography, vol. 7 (1973), pp. 289312, and Gingerich's essay Johannes Kepler, in Ren Taton and Curtis Wilson (eds.), Planetary Astronomy from the Renaissance to the Rise of Astrophysics, part A, Tycho Brahe to Newton (1989), pp. 5478; and William H. Donahue, Kepler, in Norriss S. Hetherington (ed.), Cosmology: Historical, Literary, Philosophical, Religious, and Scientific Perspectives (1993), pp. 239262. Biographies include Max Caspar, Kepler, trans. and ed. by C. Doris Hellman (1959, reissued with complete bibliographic references, 1993; originally published in German, 1948), the standard work; and Arthur Koestler, The Watershed: A Biography of Johannes Kepler (1960, reprinted 1984), written with a dramatic flair.Important studies in English of specific aspects of Kepler's thought are, on Mysterium Cosmographicum and Harmonice Mundi, J.V. Field, Kepler's Geometrical Cosmology (1988), a highly lucid explication; and Bruce Stephenson, The Music of the Heavens: Kepler's Harmonic Astronomy (1994), with valuable background chapters, while Stephenson's Kepler's Physical Astronomy (1987, reissued 1994) deals with the Astronomia Nova and the Epitome Astronomiae Copernicanae. Alexandre Koyr, The Astronomical Revolution: Copernicus, Kepler, Borelli (1973, reissued 1992; originally published in French, 1961), is a classic, still worth consulting. Also recommended are a collection of previously published classic studies by Curtis Wilson, Astronomy from Kepler to Newton (1989); Owen Gingerich, The Eye of Heaven: Ptolemy, Copernicus, Kepler (1993); and Arthur Beer and Peter Beer (eds.), Kepler: Four Hundred Years (1975), conference proceedings, including a supplement to the Bibliographia Kepleriana (cited above) covering the years 196775.Kepler's involvement in a major political-scientific controversy is discussed in N. Jardine, The Birth of History and Philosophy of Science: Kepler's A Defence of Tycho Against Ursus, with Essays on Its Provenance and Significance (1984); Edward Rosen, Three Imperial Mathematicians: Kepler Trapped Between Tycho Brahe and Ursus (1986); and Owen Gingerich and Robert S. Westman, The Wittich Connection: Conflict and Priority in Late Sixteenth-Century Cosmology (1988).General cultural and intellectual background is provided in Elika Fuckov et al. (eds.), Rudolf II and Prague: The Court and the City (1997), a heavily illustrated work; R.J.W. Evans, Rudolf II and His World: A Study in Intellectual History, 15761612 (1973, reissued 1984); Brian Vickers (ed.), Occult and Scientific Mentalities in the Renaissance (1984); Thomas DaCosta Kaufmann, The Mastery of Nature: Aspects of Art, Science, and Humanism in the Renaissance (1993); and Edward Grant, Planets, Stars, and Orbs: The Medieval Cosmos, 12001687 (1994). Robert S. Westman