KEPLER (KEPLERO), JOHANNES. - One of the four great founders of modern astronomy, together with Copernicus, Galileo and Newton. Born at Weil (Württemberg, Germany) on 16 March 1571, into a noble but by then greatly decayed family, K. was a cattle herder as a child; but at the age of thirteen, with the help of charitable persons, he was able to enter the Protestant Seminary of Adelberg, whence he then passed to that of Maulbronn and thence to the University of Tübingen. At Tübingen he met the astronomer Michael Mästlin, who inspired in him a great love for the science of the heavens and from whom he learned the new ideas of Copernicus, then fiercely opposed by the Lutherans (it is well known that Luther regarded Copernicus as a madman and that Melanchthon had declared that his opinions would not be tolerated) and of which he became an ardent supporter; a thing that earned him expulsion from the Seminary of Tübingen, where he lodged with other students.
In 1594 K. went to teach mathematics in a school at Graz (Styria), where he married a widow who some time later fell gravely ill; so that K. was forced to compile almanacs and horoscopes, his meager salary not sufficing to meet so many expenses. After various vicissitudes, K. came in 1599 to Prague as a collaborator of Tycho Brahe, then astronomer at the court of the emperor Rudolf II, in the compilation of his Tabulae Rudolphinae. On Tycho's death (24 Oct. 1601), K. obtained appointment as his successor, but the salary was further reduced; so that the poor astronomer, already burdened with a family, was forced into a very miserable life. Nevertheless he managed to publish in 1609 his Astronomia nova, seu physica coelestis tradita commentariis de motibus stellae Martis, that is, his major work.
But K.'s conditions worsened still further when his wife died (3 July 1611) and, shortly afterwards (20 Jan. 1612), the emperor Rudolf, his protector, also died. Having abandoned Prague, the astronomer went to Linz (Austria), where he gave lessons in mathematics and philosophy and where he took a wife again, so as to have someone to look after his numerous children; but the new union was even less fortunate than the former, since Susanna Reutlinger, who was twenty years younger than her husband, was also of a very different character. Even in misery, with incredible perseverance in work, K. published in 1622 his Harmonices mundi, where the third law of planetary motion is set forth, and later, in 1627, the Tabulae Rudolphinae, which served for a long time the astronomers who followed to calculate the positions of the planets.
In the last years of his life, because of the wars and revolts that were devastating the country, K. was forced to move to Regensburg and to Ulm, being reduced even to the miserable condition of a country steward in order to support his wife, his eleven children and himself. Finally, through the good offices of an illustrious Jesuit mathematician, Fr. Paul Guldin (discoverer of the well-known geometrical theorems that today bear his name), K. was admitted to the court of Wallenstein and in 1630 appointed professor at Rostock. But his life was by then over; stricken with pneumonia, on 15 Nov. 1630 he died, abandoned in a country inn near Regensburg. His grave, in the paupers' cemetery, remains still unknown.
K. was the first astronomer to carry out a true celestial triangulation, making use principally of the observations of Mars made by Tycho Brahe and deducing from them the three fundamental laws, which govern the motion of the planets around the sun and which, in his honor, astronomers still today call the Keplerian laws. They are the following:
I) The planets describe around the sun plane orbits with constant areal velocity. II) These orbits are ellipses of which the sun occupies one focus. III) The squares of the times taken by the planets to complete one revolution around the sun are proportional to the cubes of their mean distances from the sun.
These laws are extremely important, not only because they allow the position of the planets to be calculated exactly, but also because they serve as the basis for the theory of universal attraction, established later (1687) by Newton. In fact, with certain formulas of mechanics and infinitesimal calculus, from the first Keplerian law it is deduced that the planets are urged by an attractive force directed toward the sun; from the second law it is deduced that this force is inversely proportional to the square of their distance from the sun, and from the third law it is deduced that the masses of the planets are extremely small compared with the mass of the sun, which thus constitutes the barycenter of the entire planetary system.
It is also to K.'s credit that he perfected the telescope and constructed a sufficiently exact table of astronomical refraction in his Optica ad Vitellionem (dedicated to Fr. Witelo, a Polish Dominican, who had occupied himself much with questions of optics) and then in the Dioptrica.
Bibliography3 works
Giuseppe Armellini