Johannes Kepler

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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 lawsKepler's laws,
three mathematical statements formulated by the German astronomer Johannes Kepler that accurately describe the revolutions of the planets around the sun. Kepler's laws opened the way for the development of celestial mechanics, i.e.
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. 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.


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

Kepler, Johannes

(religion, spiritualism, and occult)

Johannes Kepler, the last Western astronomer of note to believe in astrology, was born on January 6, 1571, in Weil, Württemberg, Germany. He studied the elliptical orbits of the planets and discovered the three laws of planetary motion that were to lead to Newton’s law of universal gravitation. In 1600, Kepler became assistant to Tycho Brahe, succeeding him as court astronomer to Rudolf II. Kepler was deeply mystical, and many of his astronomical discoveries were motivated by a desire to demonstrate that a neoplatonic/Pythagorean mathematical order governed the heavens.

The son of peasants, Kepler erected horoscopes and published almanacs to supplement his income as court astronomer. On the title page of De fundamentis, Kepler inscribed, “Discover the force of Heavens O Men: once recognized it can be put to use.” He asserted that astrological influence “is so convincing that it can be denied only by those who had not examined it.” He also said, “We cannot deny the influence of the stars, without disbelieving in the wisdom of God.”

In much the same way as Saint Thomas Aquinas, Kepler felt that human beings could rise above planetary influences. As do contemporary astrologers, he thus cast his predictions in terms of tendencies and probabilities rather than in terms of absolute fate. Kepler’s contribution to astrology was his general theory of aspects, and he also invented the quintile, the biquintile, and the sesquiquadrate. Kepler died November 15, 1630.

Kepler is well known to modern science as the discoverer of the three laws of planetary motion named after him. His achievements were momentous, coming on the heels of the Copernican revolution and creating an astronomy of the solar system that was vastly superior to that existing before.

As an astrologer, Kepler’s achievements were equally, if not more, substantial. Like his contemporary, Shakespeare, he was “myriad minded.” His thinking ranged from the most traditionally Judeo-Christian and Pythagorean in his mysticism, to the most astonishingly modern in his more scientific thinking modes. Full of apparent contradictions, he was in reality the most complex of thinkers in astronomy and astrology, and yet, in some ways, was fundamentally quite consistent. Furthermore, he was a superb writer—lucid and simple, and capable of describing great intricacies clearly, as well as clothing some of his thoughts in magnificent poetic metaphors.

The supposed separation of astronomy and astrology is actually an illusion as far as Kepler was concerned. The contemporary scientific community in particular has all too often been the victim of this illusion, and has oversimplified Kepler’s alleged “attacks” on astrology, which are actually heated objections to “bad” astrology and nothing more. The following in particular is a case in point, from his Tertius Interveniens:

This curiosity [about astrology] flourishes, and stimulates one to learn astronomy. And astronomy is not rejected, but highly praised, as is appropriate. Now this Astrology is a foolish daughter …. But dear Lord, what would happen to her mother, the highly reasonable Astronomy, if she did not have this foolish daughter. The world, after all, is much more foolish, indeed is so foolish, that this old sensible mother, Astronomy, is talked into things and put to the lie as a result of her daughter’s foolish pranks …. The mathematician’s pay would be so low, that the mother would starve, if the daughter did not earn anything.

As devastating as this may seem to astrologers, the passage is not really a condemnation of all astrology. His thoughts must be understood to mean the popular forms of astrology, which he condemned unequivocally.

As for the accusation that astronomers would starve if they did not do horoscopes for pay—this may have some truth in it, but it does not mean that Kepler had to cheapen his science of astronomy by using the popular astrology of “the daughter.” And he did cast and interpret horoscopes for pay, but his astrology is on a very high level indeed, as is shown by the two extant delineations of Generalisimus Wallenstein’s birth chart (1608 and 1625), and others.

And such astrology was, for Kepler, to be included under astronomy. This astrology/astronomy was Kepler’s true vocation up to the point in 1619 when he transcended it, but still made it part of a greater scheme of the universe that he called Harmonice Mundi (World Harmony), the title of his last major book (1619). Even after then, he still spoke of astrology in these terms, as noted in Die Astrologie des Johannes Kepler: “Philosophy, and therefore genuine astrology, is a testimony of God’s works and is therefore holy. It is by no means a frivolous thing. And I, for my part, do not wish to dishonor it.” That this “genuine astrology” was effective is well proven by the fact that Kepler predicted the manner and time of Wallenstein’s death well in advance.

Many astrologers will at first feel offended by Kepler. He was as outspoken against some astrologers as he was against those who condemned astrology. This is seen mainly in his 1610 book Tertius Interveniens (Third Party Intervening), in which he takes a “third party” position between those who flatly condemn astrology and those who accept as true everything said in its name. He draws sharp lines between his perceptions of genuine and false practices of the art.

Like Friedrich Nietzsche, his fellow countryman of three centuries later, Kepler was a thinker who skillfully required readers to ponder issues thoroughly while being challenged, irritated, even infuriated. This process is so valuable in helping to gain ever deeper insights. It is advisable at times, when he is attacking with fury, to keep in mind that, like his earlier fellow countryman, Martin Luther, he was a reformer. He definitely did not propose that astrology be abolished, any more than Luther intended to destroy Christianity.

The foundation of his astrology was geometry and, more widely, a universal harmony present in geometry, as demonstrated in Tertius Interveniens: “Within this lower world a spiritual nature is concealed that can operate through geometry, which is vitalized through the geometrical and harmonic connections ….”; “The geometry or harmony of aspects is not between the stars in the sky, but is located rather down here on earth in the point that collects all their rays.” This principle led him to his specific contributions to astrology, among which are: his analysis of planetary interrelationships through Platonic solids; his discovery of additional aspects (the quintile and semisquare); and his cataloging and comments on the fixed stars. Beyond these accomplishments, his theory and philosophy of are indeed major contributions.

—Ken Negus


Brau, Jean-Louis, Helen Weaver, and Allan Edmands. Larousse Encyclopedia of Astrology. New York: Plume, 1980.
Kepler, Johannes. Harmonices Mundi.
Kepler. Tertius Interveniens.
Kitson, Annabella, ed. History and Astrology: Clio and Urania Confer. London: Mandala, 1989.

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.


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


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