Page 427 - Western Civilization A Brief History, Volume I To 1715 9th - Jackson J. Spielvogel

The Copernican System. The Copernican system was presented in On the Revolutions of the Heavenly Spheres, published in 1543 shortly before Copernicus’s death. As shown in this illustration from the first edition of the book, Copernicus maintained that the sun was at the center of the universe and that the planets, including the earth, revolved around it. Moreover, the earth rotated daily on its axis. (The circles read, from the center outward: 1. Sun; 2. Mercury, orbit of 80 days; 3. Venus; 4. Earth, with the moon, orbit of 1 year; 5. Mars, orbit of 2 years; 6. Jupiter, orbit of 12 years; 7. Saturn, orbit of 30 years; 8. Immobile Sphere of the Fixed Stars.)
the numerical relationships existing between the plan- ets, he focused much of his attention on discovering the “music of the spheres.” Kepler was also a brilliant mathematician and astronomer who took a post as im- perial mathematician to Emperor Rudolf II. Using the detailed astronomical data compiled by his predecessor, Kepler derived laws of planetary motion that confirmed the heliocentric theory. In his first law, he contradicted Copernicus by showing that the orbits of the planets around the sun were not circular but elliptical, with the sun at one focus of the ellipse rather than at the center.
Kepler’s work effectively eliminated the idea of uniform circular motion as well as the idea of crystal- line spheres revolving in circular orbits. The basic structure of the traditional Ptolemaic system had been disproved, and people had been freed to think in new ways of the paths of planets revolving around the sun. By the end of Kepler’s life, the Ptolemaic sys- tem was rapidly losing ground to the new ideas. Im- portant questions remained unanswered, however. What were the planets made of? And how could
motion in the universe be explained? It was an Italian scientist who achieved the next important break- through to a new cosmology by answering the first question.
Galileo
Galileo Galilei (1564–1642) taught mathematics, first at Pisa and later at Padua, one of the most prestigious universities in Europe. Galileo was the first European to make systematic observations of the heavens by means of a telescope, thereby inaugurating a new age in astronomy. He had heard of a Flemish lens grinder who had created a “spyglass” that magnified objects seen at a distance and soon constructed his own. Instead of peering at terrestrial objects, Galileo turned his telescope to the skies and made a remarkable series of discoveries: mountains and craters on the moon, four moons revolving around Jupiter, the phases of Venus, and sunspots. Galileo’s observations demolished yet another aspect of the traditional cosmology in that the universe seemed to be composed of a material
Toward a New Heaven: A Revolution in Astronomy 389
Copyright 2017 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
Image Select/Art Resource, NY