11/17/02

period 1

Nicolaus Copernicus was a Polish astronomer who wrote On the Revolutions of the Heavenly Spheres. In this book, he challenged the Ptolemaic system in the most conservative manner possible. The Ptolemaic system assumed that the Earth was the center of the universe. Above the Earth lay a series of crystalline spheres, which contained the sun, moon, stars, and other planets. Copernicus said that if the Earth were assumed to move about the sun in a circle, many of the difficulties with the Ptolemaic systems would disappear or become simpler. The motive behind this shift away from the Earth-centered universe was to find a solution to the problems of planetary motion. By allowing the Earth to move around the sun, Copernicus was able to construct a more mathematically elegant basis for astronomy. He had been discontented with the traditional system because it was mathematically clumsy and inconsistent. The primary appeal of his new system was its mathematical aesthetics. A change in the conception of the position of the Earth meant that the planets were actually moving in circular orbits and only seemed to be doing otherwise because of the position of the observers on Earth.

The next major step toward the conception of a sun-centered system was taken by Tycho Brahe. He suggested that the moon and the sun revolved around the Earth and that the other planets revolved around the sun. Brahe’s idea was based on a series of new naked-eye astronomical observations. Brahe constructed the most accurate tables of observations that had been drawn up for centuries.

When Brahe died, these tables came into the possession of Johannes Kepler, a German astronomer. Kepler was a Copernican, but not for mathematical reasons. Kepler was deeply influenced by Renaissance Neoplatonism, which held the sun in special honor. H e was determined to find mathematical harmonies in Brahe’s numbers that would support a sun-centered universe. After much work Kepler discovered that to keep the sun at the center of things, he must abandon the Copernican concept of circular orbits. The mathematical relationships that emerged from a consideration of Brahe’s observations suggested that the orbits of the planets were elliptical. However, none of the available theories could explain why the planetary orbits were elliptical.

Through the telescope, a recently invented instrument, Galileo Galilei was able to see stars where none had been known to exist, mountains on the moon, spots moving across the sun, and moons orbiting Jupiter. The heavens were far more complex than anyone had formerly suspected. Though none of these discoveries proved that the Earth orbited the sun, they did suggest the complete inadequacy of the Ptolemaic system.

Englishman Isaac Newton drew on the work of his predecessors and his own brilliance to solve the major remaining problem of planetary motion and to establish a basis for physics that endured more than two centuries. Newton reasoned that the planets and all other physical objects in the universe moved through mutual attraction, or gravity. Every object in the universe affected every other object through gravity. The attraction of gravity explained why the planets moved in an orderly rather than a chaotic manner. He had found that “the force of gravity towards the whole planet did arise from and was compounded of the forces of gravity towards all its parts, and towards every one part was in the inverse proportion of the squares of the distances from the part.”

The most important contribution was made by Johannes Kepler. He used the work of Copernicus and Brahe to formulate his belief that the sun was the center of the universe and that the orbits of the planets were elliptical. His work was a stepping stone to Newton’s work, which completed Kepler’s theories by explaining gravity’s role in the planetary orbits.

Francis Bacon believed that human knowledge should produce useful results. In particular, knowledge of nature should be brought to the aid of the human condition. These goals require the modification or abandonment of scholastic modes of learning and thinking. By directing scientists toward an examination of empirical evidence, Bacon hoped that they would achieve new knowledge and thus new capabilities for humankind.

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