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- Kepler’s reformation of astronomy was of a piece with his reform of astrology’s principles and Tycho’s radical improvement of the celestial observations. Just as the spacing of the planets bore a close relation to the polyhedral forms, so, too, Kepler regarded only those rays hitting Earth at the right harmonic angles to be efficacious.
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Dec 22, 2023 · The basis for everything we understand about the orbits of the planets comes from the work of German astronomer Johannes Kepler. Kepler, without knowing about the force of gravity,...
- Overview
- Astronomical work of Johannes Kepler
The ideas that Kepler would pursue for the rest of his life were already present in his first work, Mysterium cosmographicum (1596; “Cosmographic Mystery”). Kepler had become a professor of mathematics at the Protestant seminary in Graz, Austria, in 1594, while also serving as the district mathematician and calendar maker. In 1595, while teaching a class, Kepler experienced a moment of illumination. It struck him suddenly that the spacing among the six Copernican planets might be explained by circumscribing and inscribing each orbit with one of the five regular polyhedrons. Since Kepler knew Euclid’s proof that there can be five and only five such mathematical objects made up of congruent faces, he decided that such self-sufficiency must betoken a perfect idea. If now the ratios of the mean orbital distances agreed with the ratios obtained from circumscribing and inscribing the polyhedrons, then, Kepler felt confidently, he would have discovered the architecture of the universe. Remarkably, Kepler did find agreement within 5 percent, with the exception of Jupiter, at which, he said, “no one will wonder, considering such a great distance.” He wrote to Maestlin at once: “I wanted to become a theologian; for a long time I was restless. Now, however, behold how through my effort God is being celebrated in astronomy.”
Had Kepler’s investigation ended with the establishment of this architectonic principle, he might have continued to search for other sorts of harmonies; but his work would not have broken with the ancient Greek notion of uniform circular planetary motion. Kepler’s God, however, was not only orderly but also active. In place of the tradition that individual incorporeal souls push the planets and instead of Copernicus’s passive, resting Sun, Kepler posited the hypothesis that a single force from the Sun accounts for the increasingly long periods of motion as the planetary distances increase. Kepler did not yet have an exact mathematical description for this relation, but he intuited a connection. A few years later he acquired William Gilbert’s groundbreaking book De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure (1600; “On the Magnet, Magnetic Bodies, and the Great Magnet, the Earth”), and he immediately adopted Gilbert’s theory that Earth is a magnet. From this Kepler generalized to the view that the universe is a system of magnetic bodies in which, with corresponding like poles repelling and unlike poles attracting, the rotating Sun sweeps the planets around. The solar force, attenuating inversely with distance in the planes of the orbits, was the major physical principle that guided Kepler’s struggle to construct a better orbital theory for Mars.
But there was something more: the standard of empirical precision that Kepler held for himself was unprecedented for his time. The great Danish astronomer Tycho Brahe (1546–1601) had set himself the task of amassing a completely new set of planetary observations—a reform of the foundations of practical astronomy. In 1600 Tycho invited Kepler to join his court at Castle Benátky near Prague. When Tycho died suddenly in 1601, Kepler quickly succeeded him as imperial mathematician to Holy Roman Emperor Rudolf II. Kepler’s first publication as imperial mathematician was a work that broke with the theoretical principles of Ptolemaic astrology. Called De Fundamentis Astrologiae Certioribus (1601; Concerning the More Certain Fundamentals of Astrology), this work proposed to make astrology “more certain” by basing it on new physical and harmonic principles. It showed both the importance of astrological practice at the imperial court and Kepler’s intellectual independence in rejecting much of what was claimed to be known about stellar influence. The relatively great intellectual freedom possible at Rudolf’s court was now augmented by Kepler’s unexpected inheritance of a critical resource: Tycho’s observations. In his lifetime Tycho had been stingy in sharing his observations. After his death, although there was a political struggle with Tycho’s heirs, Kepler was ultimately able to work with data accurate to within 2′ of arc. Without data of such precision to back up his solar hypothesis, Kepler would have been unable to discover his “first law” (1605), that Mars moves in an elliptical orbit. At one point, for example, as he tried to balance the demand for the correct heliocentric distances predicted by his physical model with a circular orbit, an error of 6′ or 8′ appeared in the octants (assuming a circle divided into eight equal parts). Kepler exclaimed, “Because these 8′ could not be ignored, they alone have led to a total reformation of astronomy.” Kepler’s reformation of astronomy was of a piece with his reform of astrology’s principles and Tycho’s radical improvement of the celestial observations. Just as the spacing of the planets bore a close relation to the polyhedral forms, so, too, Kepler regarded only those rays hitting Earth at the right harmonic angles to be efficacious.
During the creative burst of the early Prague period (1601–05) when Kepler won his “war on Mars” (he did not publish his discoveries until 1609 in the Astronomia Nova [New Astronomy], which contained the first two laws of planetary motion), he also wrote important treatises on the nature of light and on the sudden appearance of a new star (1606; De Stella Nova, “On the New Star”). Kepler first noticed the star—now known to have been a supernova—in October 1604, not long after a conjunction of Jupiter and Saturn in 1603. The astrological importance of the long-anticipated conjunction (such configurations take place every 20 years) was heightened by the unexpected appearance of the supernova. Typically, Kepler used the occasion both to render practical predictions (e.g., the collapse of Islam and the return of Christ) and to speculate theoretically about the universe—for example, that the star was not the result of chance combinations of atoms and that stars are not suns.
Britannica Quiz
Faces of Science
The ideas that Kepler would pursue for the rest of his life were already present in his first work, Mysterium cosmographicum (1596; “Cosmographic Mystery”). Kepler had become a professor of mathematics at the Protestant seminary in Graz, Austria, in 1594, while also serving as the district mathematician and calendar maker. In 1595, while teaching a class, Kepler experienced a moment of illumination. It struck him suddenly that the spacing among the six Copernican planets might be explained by circumscribing and inscribing each orbit with one of the five regular polyhedrons. Since Kepler knew Euclid’s proof that there can be five and only five such mathematical objects made up of congruent faces, he decided that such self-sufficiency must betoken a perfect idea. If now the ratios of the mean orbital distances agreed with the ratios obtained from circumscribing and inscribing the polyhedrons, then, Kepler felt confidently, he would have discovered the architecture of the universe. Remarkably, Kepler did find agreement within 5 percent, with the exception of Jupiter, at which, he said, “no one will wonder, considering such a great distance.” He wrote to Maestlin at once: “I wanted to become a theologian; for a long time I was restless. Now, however, behold how through my effort God is being celebrated in astronomy.”
Had Kepler’s investigation ended with the establishment of this architectonic principle, he might have continued to search for other sorts of harmonies; but his work would not have broken with the ancient Greek notion of uniform circular planetary motion. Kepler’s God, however, was not only orderly but also active. In place of the tradition that individual incorporeal souls push the planets and instead of Copernicus’s passive, resting Sun, Kepler posited the hypothesis that a single force from the Sun accounts for the increasingly long periods of motion as the planetary distances increase. Kepler did not yet have an exact mathematical description for this relation, but he intuited a connection. A few years later he acquired William Gilbert’s groundbreaking book De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure (1600; “On the Magnet, Magnetic Bodies, and the Great Magnet, the Earth”), and he immediately adopted Gilbert’s theory that Earth is a magnet. From this Kepler generalized to the view that the universe is a system of magnetic bodies in which, with corresponding like poles repelling and unlike poles attracting, the rotating Sun sweeps the planets around. The solar force, attenuating inversely with distance in the planes of the orbits, was the major physical principle that guided Kepler’s struggle to construct a better orbital theory for Mars.
But there was something more: the standard of empirical precision that Kepler held for himself was unprecedented for his time. The great Danish astronomer Tycho Brahe (1546–1601) had set himself the task of amassing a completely new set of planetary observations—a reform of the foundations of practical astronomy. In 1600 Tycho invited Kepler to join his court at Castle Benátky near Prague. When Tycho died suddenly in 1601, Kepler quickly succeeded him as imperial mathematician to Holy Roman Emperor Rudolf II. Kepler’s first publication as imperial mathematician was a work that broke with the theoretical principles of Ptolemaic astrology. Called De Fundamentis Astrologiae Certioribus (1601; Concerning the More Certain Fundamentals of Astrology), this work proposed to make astrology “more certain” by basing it on new physical and harmonic principles. It showed both the importance of astrological practice at the imperial court and Kepler’s intellectual independence in rejecting much of what was claimed to be known about stellar influence. The relatively great intellectual freedom possible at Rudolf’s court was now augmented by Kepler’s unexpected inheritance of a critical resource: Tycho’s observations. In his lifetime Tycho had been stingy in sharing his observations. After his death, although there was a political struggle with Tycho’s heirs, Kepler was ultimately able to work with data accurate to within 2′ of arc. Without data of such precision to back up his solar hypothesis, Kepler would have been unable to discover his “first law” (1605), that Mars moves in an elliptical orbit. At one point, for example, as he tried to balance the demand for the correct heliocentric distances predicted by his physical model with a circular orbit, an error of 6′ or 8′ appeared in the octants (assuming a circle divided into eight equal parts). Kepler exclaimed, “Because these 8′ could not be ignored, they alone have led to a total reformation of astronomy.” Kepler’s reformation of astronomy was of a piece with his reform of astrology’s principles and Tycho’s radical improvement of the celestial observations. Just as the spacing of the planets bore a close relation to the polyhedral forms, so, too, Kepler regarded only those rays hitting Earth at the right harmonic angles to be efficacious.
During the creative burst of the early Prague period (1601–05) when Kepler won his “war on Mars” (he did not publish his discoveries until 1609 in the Astronomia Nova [New Astronomy], which contained the first two laws of planetary motion), he also wrote important treatises on the nature of light and on the sudden appearance of a new star (1606; De Stella Nova, “On the New Star”). Kepler first noticed the star—now known to have been a supernova—in October 1604, not long after a conjunction of Jupiter and Saturn in 1603. The astrological importance of the long-anticipated conjunction (such configurations take place every 20 years) was heightened by the unexpected appearance of the supernova. Typically, Kepler used the occasion both to render practical predictions (e.g., the collapse of Islam and the return of Christ) and to speculate theoretically about the universe—for example, that the star was not the result of chance combinations of atoms and that stars are not suns.
Britannica Quiz
Faces of Science
Kepler’s discoveries turned Nicolaus Copernicus’s 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.
- Johannes Kepler was an astronomer. He originally studied to be a theologian at the University of Tübingen. He became very interested in astronomy,...
- Johannes Kepler is best known for his three laws of planetary motion. These laws are:
- Johannes Kepler and his laws were a great influence on Isaac Newton. Newton came up with a law of gravity, which states that masses attract each ot...
- Johannes Kepler was born on December 27, 1571, in the town of Weil der Stadt in the duchy of Württemberg, now in Germany.
- After contracting a fever, Johannes Kepler died on November 15, 1630, in Regensburg, in the duchy of Bavaria, now in Germany. He had gone to Regens...
Nov 13, 2023 · Like most astronomers of his day, Kepler was an astrologer, but he tried to reform the way astrology was done and maintained it had limited validity. Kepler had originally studied for the ministry and wrote a number of theological works.
Aug 16, 2009 · She shows how Kepler's philosophy paved the way for the discovery of elliptical orbits and provided a defense of physical astronomy's methodological soundness. In doing so, Martens demonstrates how an empirical discipline was inspired and profoundly shaped by philosophical assumptions.
- Rhonda Martens
- August 16, 2009
- 2000
The person who finally produced a model of planetary motion that was both simple and accurate was not Copernicus but the German mathematician, Johannes Kepler (1571-1630). He formulated the basic mathematical laws of planetary motion which have been retained ever since.
Kepler’s book for the first time argued strongly for a physical basis to astronomical explanations. Galileo’s work showed that a coherent understanding was more important for scientific progress than specific proofs.
