Kepler, Johannes

Kepler, Johannes (yōhä`nəs kĕp`lər), 1571–1630, German astronomer. From his student days at the Univ. of Tübingen, he was influenced by the Copernican teachings. From 1593 to 1598 he was professor of mathematics at Graz and while there wrote his Mysterium cosmographicum (1596). This work opened the way to friendly intercourse with Galileo and Tycho Brahe, and in 1600 Kepler became Tycho's assistant in his observatory near Prague. On Tycho's death (1601) Kepler succeeded him as court mathematician to Holy Roman Emperor Rudolf II. In 1609 he published the results of Tycho's calculations of the orbit of Mars. In this celebrated work were stated the first two of what became known as Kepler's laws. In 1612, becoming mathematician to the states of Upper Austria, he moved to Linz. He wrote an epitome of the astronomy of Copernicus in 1618, and in 1619 De cometis and Harmonice mundi (in which was announced the third of Kepler's laws). In 1626, Kepler moved to Ulm. After his death his manuscript writings, bought by Catherine II of Russia, were placed in the observatory of Pulkovo.

Bibliography

See biographies by M. Caspar (tr. 1959, repr. 1962) and A. Armitage (1966); A. Beer, ed., Kepler: Four Hundred Years (1974).

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Kepler, Johannes

(born Dec. 27, 1571, Weil der Stadt, Württemberg—died Nov. 15, 1630, Regensburg) German astronomer. Born into a poor family, he received a scholarship to the University of Tübingen. He received an M.A. in 1594, after which he became a mathematics teacher in Austria. He developed a mystical theory that the cosmos was constructed of the five regular polyhedrons, enclosed in a sphere, with a planet between each pair. He sent his paper on the subject to Tycho Brahe, who invited Kepler to join his research staff. In attempting to understand atmospheric refraction of light, he became the first to explain accurately how light behaves within the eye, how eyeglasses improve vision, and what happens to light in a telescope. In 1609 he published his finding that the orbit of Mars was an ellipse and not the perfect circle hitherto presumed to be the orbit of every celestial body. This fact became the basis of the first of Kepler's three laws of planetary motion. He also determined that planets move faster as they near the Sun (second law), and in 1619 he showed that a simple mathematical formula related the planets' orbital periods to their distance from the Sun (third law). In 1620 he defended his mother from charges of witchcraft, thereby preserving his own reputation as well.

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Kepler, Johannes 

Born Dec. 27, 1571, in Weil der Stadt, Württemberg; died Nov. 15, 1630, in Regensburg, Bavaria. German astronomer who discovered the laws of planetary motion.

Kepler was born into a poor Protestant family. After studying in a monastery school, he enrolled in 1589 in the theological seminary of the Academy (later, University) of Tübingen, from which he graduated with a bachelor’s degree. In 1591 he enrolled in the Academy of Tübingen, where he completed his education. Kepler’s professor of mathematics and astronomy, M. Mästlin, privately acquainted him with the Copernican heliocentric system of the world, although he himself was obliged to teach astronomy according to the geocentric system of Ptolemy. Kepler obtained a master’s degree in 1593, but, accused of independence of spirit, he was not permitted to devote himself to the church and was directed to teach mathematics at the Gymnasium in Graz (Austria). There Kepler wrote his first major work, Mysterium cosmographicum (1596), in which he attempted to establish a numerical relationship between the distances of the planets from the sun and the dimensions of regular polyhedrons. The book is of no scientific significance, but in it Kepler already showed himself to be a consistent adherent of Copernicus’ theory. Religious persecution by the Catholics forced Kepler to leave Graz. In 1600 he moved to Prague to the eminent astronomer Tycho Brahe. After the latter’s death in 1601, he inherited the data that Tycho had gathered from highly precise observations over many years.

In Prague, Kepler published a series of works, including the treatise Ad Vitellionem Paralipomena, quibus astronomiae pars optica traditur (1604) on the application of optics in astronomy, in which he analyzed astronomical refraction and noted the glow appearing around the sun during a total solar eclipse—the solar corona. With this work he became the first to state the law of the decrease in illuminance in inverse proportion to the square of the distance from the source. In another treatise, Dioptrice (1611), Kepler described a telescope he designed (the Keplerian telescope), the prototype of modern refractors.

Kepler’s most important work was Astronomia nova (1609), which was devoted to the study of the motion of Mars on the basis of Tycho’s observations. The work contained the first two laws of planetary motion (seeKEPLER'S LAWS), which he established for Mars on the basis of a prodigious amount of computations. In 1612, Kepler moved to Linz, where De harmonice mundi appeared in 1619; in this work he formulated the third law, which unites the theory of motion of all the planets into a harmonious whole. His work Epitome astronomiae Copernicanae (parts 1–2, 1618–22) contains the conclusion that the first two laws, which were established for Mars, are applicable to all the planets and to the motion of the moon around the earth and that the third law is also applicable to the four satellites of Jupiter. In this work Kepler set forth a theory and a method of predicting solar and lunar eclipses. Striving to discredit the doctrine of Copernicus, the Vatican immediately placed this work of Kepler’s on its list of prohibited books. In 1619, Kepler published the treatise De cometis.

The end of Kepler’s life was darkened by wandering and poverty. The Thirty Years’ War, which had begun, and the intensification of the Catholic persecution of Protestants compelled Kepler to seek refuge in Ulm. There he completed (1627) his last major work, the Tabulae Rudolphinae, which summed up the results of many years of analysis of Tycho’s observations. The tables made it possible to calculate in convenient form the positions of the planets for any moment of time with an accuracy unusually high for that time. The ephemerides calculated by Kepler on the basis of the tables allowed him to predict the transit of Venus across the sun’s disk that took place in 1631. In 1628, in pursuit of a means of subsistence, Kepler became astrologer to General A. von Wallenstein and lived until 1630 in Sagan (now Żagań, Poland). Kepler’s last work was the fantasy Somnium, which was published only after his death (1634). In November 1630, Kepler traveled to Regensburg; he fell ill en route and died soon after his arrival in the city. His manuscripts are preserved in the USSR in Leningrad. In 1808 a monument was erected to him in Regensburg, and in 1870 in Weil.

Kepler’s entire life was devoted to the substantiation and development of the heliocentric doctrine of Copernicus. The most important argument in favor of the central position of the sun is Kepler’s three laws, which put an end to the previous conception of uniform circular motions of the celestial bodies. The sun, which occupies one of the foci of a planet’s elliptical orbit, is, according to Kepler, the source of the force that moves the planets. Kepler’s laws, which are the permanent basis of theoretical astronomy, were explained by Newtonian mechanics, particularly by the law of universal gravitation. Kepler himself had already discussed the “gravity” acting between celestial bodies and explained the tides of the earth’s oceans by the action of the moon.

Kepler published many books and articles. His remarkable mathematical abilitites were manifested not only in astronomical works but also in the study of problems involving the measurement of volumes (Nova stereometria doliorum, 1615), for which Kepler proposed a method containing the rudiments of infinitesimal analysis. Using the idea of the method of indivisibles known to him from the works of Archimedes, Kepler found by original procedures the volume of many solids of revolution. Immediately after the discovery of logarithms, Kepler proposed a detailed theory of their use for calculations (1614) and compiled tables of logarithms similar in structure to modern tables (1624).

Kepler’s world view was not alien to Pythagorean ideas, or even mysticism. He was considered one of the greatest astrologers of his time, although he practiced astrology primarily to earn a living.

Kepler’s discoveries were important historically, becoming the basis for the further development of astronomy.

WORKS

Gesammelte Werke, vols. 1–18. Munich, 1937–69.

REFERENCES

Eremeeva, A. I. Vydaiushchiesia astronomy mira. Moscow, 1966.
Caspar, M. Iohannes Kepler. Stuttgart, 1950.