Kepler, Johannes(1571-1630)
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German astronomer, whose studies of the motions of the planets helped materially in laying the foundations of modern dynamic astronomy. He was born on December 27, 1571, at Württemberg. His father was petty officer in the duke of Württemberg’s army and his mother, Catharine , came of a family of once noble standing. Johannes was two months premature infant and a vary delicate child. With his younger brother Heinrich, he lived with his grandparents while his father was engaged in the Dutch wars and his mother accompanied her husband to the Netherlands. When about four years of age he contracted smallpox and nearly went blind with the result that his eyesight was permanently impaired.
He firs attended school in Weil, then in Leon berg on the return of his parents, and family in Convent schools of Adelberg( 1584). In September 1588 he obtained his bachelors degree. He had hoped to enter the ministry but instead was persuaded to accept the post f professor of mathematics at Graz in 1594.
At Tubingen Kepler came under the influence of Michael Maestlin who became a lifelong friend. Maestlin was a protagonist of the views of Copernicus which he had to teach privately to his young pupil as the Ptolemaic system was still the picture of the universe which was held in official circles. Kepler absorbed the heliocentric concept of Copernicus and later developed it with a pertinacity and brilliance for which he will ever be remembered.
As professor of Graz, Kepler lectured on mathematics and also, at the request of the university , on Virgil and rhetoric. He was also expected to prepare annual almanacs giving astronomical and astrological predictions and so he applied himself with great diligence to the study of astrology. No disparagement should be attached to Kepler for his Astrological Work because at the close of the 16th century not only was the conception widely held that the stars and planets exerted a definite influence on day to day events, but there were no clear ideas of the forces which caused planetary motion; moreover the concept of the difference between the behavior of heavenly bodies and terrestrial phenomena was still unquestioned and thus even as independent and penetrating a mind as Kepler’s could accept the basic doctrine of astrological influence. Soon after taking up his appointment, therefore , he published (1595) his Calendrium und Prognosticum computed for the years 1591- 99.
Kepler was, however, primarily interested in problems of the planetary system. Because of his firm Faith in God and in the order of Creation , he believed with almost fanatical fervor the orbits of the planets and he spent his major efforts in seeking this relationship. The first fruits of his labors were published in 1596 under the title Prodromus Dissertationum Mathematicarum continens Mysterium Cosmographicum. Although a youthful work, Kepler showed here his freedom of mind and his ability to speculate in Scientific manner on problems of great significance and complexity. The hypothesis presented in the Mysterium Cosmographium was ingenious: Kepler found that between the “spheres” of six planets there could be fitted the five “regular” solides and believed that he had thus discovered a basic order underlying the distances of the planets from the sun. the publication of his work brought him fame and he began corresponding on very friendly terms with Thycho Brahe and Galileo, two of the most eminent astronomers of the day.
In April of the Following year, Kepler married the Wealthy Barbara von Muhleck, whom he had met in Graz , but by September all protestant theologians were expelled from the city, Although his wife’s influence enabled him to return after but one month away. However, the situation remained unfavorable and in 1599 he asked Maestlin to help him obtain a chair at Tubingen . He met with no success and, finally, in 1600, Kepler and his wife had to leave Graz. The Roman Catholic Hensart von Hohenberg, who was an old pupil of Maestlin’s and with whom Kepler had been in correspondence, suggested that Tycho Brahe might help. Tycho himself had been forced to leave the island of Hveen but when appointed court mathematical to Emperor Rudolf II in Prague invited Kepler to join him there and, two months after leaving Graz, Kepler and his wife made their home in Prague.
Tycho died a year after Kepler arrived in Prague and he was there pun appointed by the emperor to succeed his late patron as court Mathematician (although at a reduced salary). All the observations which Tycho had made were at kepler’s disposal and, as later events proved, these were a vertable storehouse of information to which astronomy will ever be in dept. the Emperor had , however, astrological learnings and in 1602 in The De fundamentalists astrological certioribus, his first publication from Prague, Kepler declared his aim of distilling and preserving the grain of truth which he believed astrology to possess.
Although he had no liking for this Kind of well paid activity, Kepler believed that a means of subsistence was provided for all humans and classed astrology as the means of assisting astronomers in their work. In 1606 another small publication De Stella nova in pede serpentarii. But much more important was the publication in 1604 of the Astronomiae pars optic. This book contained Kepler’s fundamental ideas on the nature of vision and a definition of a ray of light which later became generally adopted in geometrical optics. There was also offered an explanation of the reflection of light and notable approximation to the law of refraction.
From the time he came to Tycho, Kepler paid particular attention to the observation of Mars, the movements of which, because of its comparatively large eccentricity, had always been difficult to account for by means of the customary, had always been difficult to account for by means of the customary circular motion. It was in his efforts to reconcile the observations with the Copernican system that Kepler was led to take the bold step which had so profound an effect an future astronomy and made an complete break with traditions of more than 2000 years. He proposed first that the planets revolved round the sun in elliptical paths with the sun at one focus. Next, with his belief in the order and regularity of the heavens , he sought some kind of regular motion which would describe the behavior of the planets in paths of elliptical form. Such work entailed much labor but finally he discovered that the radius vector of each planet described equal areas of the ellipse in equal times. Thus he accounted precisely for the irregular velocity of a planet in its orbit and obviated the need for epicycle. This new fundamental important work was published in Prague in 1609 in Kepler’s 36th year. Beside making public the two laws of planetary motion, the book contained a discussion of celestial forces and extended ideas first enunciated 13 years earlier I his Mysterium Cosmographicum. He supposed that some kind of force emanated from the sun and that its magnitude being proportional to the length of the radius vector. The orbital motion of the sun on its axis and the whole concept was, in fact, a theory of vortexes. This explanation was the first attempt to formulate a physical mechanism to account for the motion of the planets; that it was not satisfactory is no discredit to Kepler for it was based on the 16th century belief that a force must be constantly applied to a body in order to keep it in motion. In the same year Kepler published also the Mercurius in Sole on a transit of Mercury and in 1610, after observing with a Galilean telescope, he published the Narratio de Observatis a se quatuor Jovis Satellibus erronibus. The year 1610 also saw the Tertius Interveniens on astrology and a publication on Galileo’s Nunico Sidereo.
The use of the newly invented telescope stimulated Kepler to further optical studies and in 1611 his Dioptrice appeared. In this the design of the inverting astronomical telescope which, with modification, came later into wide use , was first suggested.
Political disturbance were occurring in Prague. Matthias brother of the emperor Rudolf, assumed the throne in 1611 and the next year Rudolf died. Fortunately Kepler’s loyalty to Rudolf did not prevent his being favored by Matthias and in 1612 he was appointed mathematician to the states of upper Austria. In 1613, with the new emperor, he advocated the introduction of the Gregorian calendar but was frustrated by antipapal prejudice. During this year he married an orphan, Susanna Reutlinger, his wife Barbara having died two years earlier.
In 1613 an abundant vintage drew Kepler’s attention to the methods used for determining the cubical contents of vessels. His thoughts on this appeard in 1615, in the Nova stereometria Doliorium, which could be said to have prepared the way for the development of the infinitesimal calculus. Some theological writings appeared in 1614 and 1615, and in 1618 observations of three comets gave rise to De Cometis(1616) wherein Kepler suggested that comets were condensations in the ether and moved in straight lines due to impulses received from the sun.
Kepler extended his planetary laws to the satellites of Jupiter in the Epitome astronomiae copernicanae published in parts between 1618 and 1620-21 and which is notable for its emphasis on physical explanations. The third planetary law connecting the periods and mean distances of the planets had seen the light of day in 1619 in his De Harmonice Mundi with which his great contribution to dynamical astronomy was completed. It was in this work that Kepler proposed the mathematical concept of “harmony” in the solar system , believing he had thus further extended his search for unification by marrying together intervals in the musical scale with the angular velocities of the planets.
He was the first to apply his three laws to the computation of ephemeredes and, to assist his work used logarithms . he wrote on the subject and published(1624) Chilias Logarithmorum.
1627 there appeared, after religious and financial delays, the Tabulae Rudolphinae. These rudolphine tables held their place for over a century, being universally used by astronomers in calculating planetary positions. This work contained also tables of refraction and logarithms and extended catalogue of 1005 stars based on Tycho’s observations of 777 star positions.
In 1628 Kepler and his family moved to Silesia where he still concerned himself ephemeredes. On November 15. 1629, in Ratisbon (Regensburg), Kepler died but left behind him achievements which helped to change the face of astronomy and ensured his permanent and deserved fame.
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