The Copernican Revolution
Halfway through the thirteenth centu ry, knowledge astronomy had spread throughout Europe as GreE manuscripts were translated into Latin in the newly founded European universities. The Renaissance blossomed in the next two centuries, ending the dominance of ecclesiastical concerns in medieval thought and beginning the development of a broader range intellectual considerations, including cosmology. Renaissance scientists proved to be creative in picturing the physical world, not letting themselves be diminated by past dogmas. They prepared the was deep change in scientific thought and viewpoint
The Coprenican System
Cultural ideas, including astronomy, proliferated after the 1430s, when the printing press was invented. Although the Ptolemaic system had been immensely successful in describing general aspects of planetary motion for over 13 centuries, by the fifteenth century easily recognizable discrepancies had arisen in the observed and predicted positions of some planets.
About the time the New World was being discovered, Nicolaus Copernicus (1473-1543), a Polish canon of ecclesiastical law and astronomer, began wondering whether any other arrangement of the planetary system might not be simpler, more reasonable, and more aesthetically pleasing than the Ptolemaic one. He resurrected Aristarchus's heliocentric idea and built a new cosmology based on it. After nearly four decades of study, Copernicus's monumental book On the Revolutions of the Heavenly Orbs was published in the year of his death, 1543. Dedicating the work to Pope Paul III, he died without seeing his theory accepted, except by a few friends to whom he had given his manuscript years before its publication. The public reception given at the time to what was much later a revolution in the concept of the universe varied between indifference and open hostility.
Because Copernicus still believed in the Greek idea that heavenly bodies must move in perfect circles, he had to explain the deviations from uniform motion. To clear those up he postulated a number of epicycles and other mathematical structures. His system, then, was not much more accurate or simpler than Ptolemy's, but the Copernican system was a tremendous step in cosmological thought for its time. The heliocentric model was as capable of explaining retrograde motion and all the observed motions as was the entric model. In the next century this change led to aceptance of the concept that celestial physics was a supernatural matter but only an extension of terrestrial physics; Isaac Newton was later to make that clear.
Tycho Brahe (1546-1601)
Appearing at an opportune time, the right man for the advance in astronomy was Danish noblemanomer Tycho Brahe. With financial help from King Frederick II he constructed in 1582 a superbly equiped observatory on the island of Hveen, about ometers northeast of Copenhagen. There, with ost accurate pretelescopic observing instruever designed, Brahe determined positions with a precision of one minute of arc, far surpassing evious measurements.
Brahe observed the sun, moon, and stars regularly instead of haphazardly as others had in the past. An uninterrupted record of their movements over many years was thus available for study and analysis. Brahe had reservations about adopting the entire helio-centric theory. He accepted the idea that the five planets revolved around the sun but not the idea that the and sluggish earth moved. Earth's motion be felt, he argued - and besides, a moving las contrary to scriptural belief. Neither could he detect the earth's orbital motion by parallactic shifts in the positions of the brighter stars. Consequently Brahe's cosmological system was a comproThe planets orbited the sun; the sun and moon, ,orbited a fixed earth. There was relatively little interest in Brahe's cosmology, and it never really won a in cosmological thought.
Johannes Keppler (1571-1630)
In the years just prior to 1600 the Renaissance and ation were coming to an end. Copernicus's ere read by a few astronomers who recognized computational advantages of the Cosystem but were not willing to take seriously ophical and physical implications. But a deCopernican, Johannes Kepler (1571-1630), the German assistant and successor to Tycho Brahe, was . to change its acceptance. Brahe's observations of the celestial bodies bore fruit in the hands er when he pulled from Brahe's records history making discoveries.
The question that concerned Kepler was what the clockwork was that governed the celestial machinery. After 17 years of labor, during which he rejected many ideas because they did not fit Brahe's observations, Kepler explained in two books, published in 1609 and in 1619', how the planets moved. His science was uncompromising and contributed to making today's standard: A scientific model must satisfy all observational facts or fail. By the study of the orbit of Mars," he said, "we must either arrive at the secrets of astronomy or forever remain in ignorance of them.
