Nicolaus Copernicus



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Mature Career



The new star in the constellation Cassiopeia had caused Tycho to rededicate himself to astronomy; one immediate decision was to establish a large observatory for regular observations of celestial events. His plan to establish this observatory in Germany prompted King Frederick II to keep him in Denmark by granting him title in 1576 to the island of Ven (formerly Hven), in the middle of The Sound and about halfway between Copenhagen and Helsingør, together with financial support for the observatory and laboratory buildings. Tycho called the observatory Uraniborg, after Urania, the Muse of astronomy. Surrounded by scholars and visited by learned travelers from all over Europe, Tycho and his assistants collected observations and substantially corrected nearly every known astronomical record.
Tycho was an artist as well as a scientist and craftsman, and everything he undertook or surrounded himself with had to be innovative and beautiful. He established a printing shop to produce and bind his manuscripts in his own way, he imported Augsburg craftsmen to construct the finest astronomical instruments, he induced Italian and Dutch artists and architects to design and decorate his observatory, and he invented a pressure system to provide the then uncommon convenience of sanitary lavatory facilities. Uraniborg fulfilled the hopes of Tycho’s king and friend, Frederick II, that it would become the centre of astronomical study and discovery in northern Europe.
But Frederick died in 1588, and under his son, Christian IV, Tycho’s influence dwindled; most of his income was stopped, partly because of the increasing needs of the state for money. Spoiled by Frederick, however, Tycho had become both unreasonably demanding of more money and less inclined to carry out the civic duties required by his income from state lands.

At odds with the three great powers—king, church, and nobility—Tycho left Ven in 1597, and, after short stays at Rostock and at Wandsbek, near Hamburg, he settled in Prague in 1599 under the patronage of Emperor Rudolf II, who also in later years supported the astronomer Johannes Kepler.


The major portion of Tycho’s lifework—making and recording accurate astronomical observations—had already been done at Uraniborg. To his earlier observations, particularly his proof that the nova of 1572 was a star, he added a comprehensive study of the solar system and his proof that the orbit of the comet of 1577 lay beyond the Moon. He proposed a modified Copernican system in which the planets revolved around the Sun, which in turn moved around the stationary Earth. What Tycho accomplished, using only his simple instruments and practical talents, remains an outstanding accomplishment of the Renaissance.
Tycho attempted to continue his observations at Prague with the few instruments he had salvaged from Uraniborg, but the spirit was not there, and he died in 1601, leaving all his observational data to Kepler, his pupil and assistant in the final years. There was a struggle between Kepler and Tycho’s heirs regarding ownership of the data. When it was resolved, with those data Kepler laid the groundwork for the work of Sir Isaac Newton.


















Joannes Kepler


Astronomer (1571–1630)
Johannes Kepler, was a German astronomer who discovered three major laws of planetary motion, conventionally designated as follows: (1) the planets move in elliptical orbits with the Sun at one focus; (2) the time necessary to traverse any arc of a planetary orbit is proportional to the area of the sector between the central body and that arc (the “area law”); and (3) there is an exact relationship between the squares of the planets’ periodic times and the cubes of the radii of their orbits (the “harmonic law”). Kepler himself did not call these discoveries “laws,” as would become customary after Isaac Newton derived them from a new and quite different set of general physical principles. He regarded them as celestial harmonies that reflected God’s design for the universe. 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.
Among Kepler’s many other achievements, he provided a new and correct account of how vision occurs; he developed a novel explanation for the behaviour of light in the newly invented telescope; he discovered several new, semi-regular polyhedrons; and he offered a new theoretical foundation for astrology while at the same time restricting the domain in which its predictions could be considered reliable. A list of his discoveries, however, fails to convey the fact that they constituted for Kepler part of a common edifice of knowledge. The matrix of theological, astrological, and physical ideas from which Kepler’s scientific achievements emerged is unusual and fascinating in its own right. Yet, because of the highly original nature of Kepler’s discoveries, it requires an act of intellectual empathy for moderns to understand how such lasting results could have evolved from such an apparently unlikely complex of ideas. Although Kepler’s scientific work was centered first and foremost on astronomy, that subject as then understood—the study of the motions of the heavenly bodies—was classified as part of a wider subject of investigation called “the science of the stars.” The science of the stars was regarded as a mixed science consisting of a mathematical and a physical component and bearing a kinship to other like disciplines, such as music (the study of ratios of tones) and optics (the study of light). It also was subdivided into theoretical and practical categories.
Besides the theory of heavenly motions, one had the practical construction of planetary tables and instruments; similarly, the theoretical principles of astrology had a corresponding practical part that dealt with the making of annual astrological forecasts about individuals, cities, the human body, and the weather. Within this framework, Kepler made astronomy an integral part of natural philosophy, but he did so in an unprecedented way—in the process, making unique contributions to astronomy as well as to all its auxiliary disciplines



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