Copernican system  (Page 3/6)

For astronomical purposes, astronomers always assumed that the Earth is as a point with respect to the heavens. Only in thecase of the Moon could one notice a parallactic displacement (about 1°) with respect to the fixed stars during its (i.e., the Earth's) diurnal motion. In Copernican astronomy onenow had to assume that the orbit of the Earth was as a point with respect to the fixed stars, and because the fixed stars did not reflect the Earth's annualmotion by showing an annual parallax    , the sphere of the fixed stars had to be immense. What was the purpose of such a large spacebetween the region of Saturn and that of the fixed stars?

These and others were objections that needed answers. The Copernican system simply did not fit into the Aristotelian wayof thinking. It took a century and a half for a new physics to be devised to undegird heliocentric astronomy. The works inphysics and astronomy of Galileo and Johannes Kepler were crucial steps on this road.

There was another problem. A stationary Sun and moving Earth also clashed with many biblical passages. Protestants andCatholics alike often dismissed heliocentrism on these grounds. Martin Luther did so in one of his "table talks" in1539, before De Revolutionibus had appeared. (Preliminary sketches had circulated in manuscriptform.) In the long run, Protestants, who had some freedom to interpret the bible personally, accepted heliocentrism somewhatmore quickly. Catholics, especially in Spain and Italy, had to be more cautious in the religious climate of the Counter Reformation    , as the case of Galileo clearly demonstrates. Christoph Clavius , the leading Jesuit mathematician from about 1570 to his death in 1612, usedbiblical arguments against heliocentrism in his astronomical textbook.

The situation was never simple, however. For one thing, late in the sixteenth century Tycho Brahe devised a hybrid geostatic heliocentric system in which the Moon and Sun went around the Earth but the planets went around theSun. In this system the elegance and harmony of the Copernican system were married to the solidity of a central and stableEarth so that Aristotelian physics could be maintained. Especially after Galileo's telescopic discoveries,many astronomers switched from the traditional to the Tychonic cosmology. For another thing, by 1600 there were still very fewastronomers who accepted Copernicus's cosmology. It is not clear whether the execution of Giordano Bruno , a Neoplatonist mystic who knew little about astronomy, had anything to do with his Copernicanbeliefs. Finally, we must not forget that Copernicus had dedicated De Revolutionibus to the Pope. During the sixteenth century the Copernican issue was not consideredimportant by the Church and no official pronouncements were made.

Galileo's discoveries changed all that. Beginning with Sidereus Nuncius in 1610, Galileo brought the issue before a wide audience. He continued his efforts, ever moreboldly, in his letters on sunspots, and in his letter to the Grand Duchess Christina (circulated in manuscript only) heactually interpreted the problematical biblical passage in the book of Joshua to conform to a heliocentric cosmology. Moreimportantly, he argued that the Bible is written in the language of the common person who is not an expert inastronomy. Scripture, he argued, teaches us how to go to heaven, not how the heavens go. At about the same time, Paolo Antonio Foscarini , a Carmelite theologian in Naples, published a book in which he argued that the Copernican theory did not conflictwith Scripture. It was at this point that Church officials took notice of the Copernican theory and placed De Revolutionibus on the Index of Forbidden Books until corrected.

Galileo's Dialogue Concerning the Two Chief WorldSystems of 1632 was a watershed in what had shaped up to be the "Great Debate." Galileo's arguments undermined thephysics and cosmology of Aristotle for an increasingly receptive audience. His telescopic discoveries, although they did not prove that the Earth moved around the Sun, added greatly to his argument. In the meantime, Johannes Kepler (who had died in 1630) had introduced physical considerations into the heavens and hadpublished his Rudolphine Tables , based on his own elliptical theory and Tycho Brahe's accurate observations, and these tables were more accurate by far than any previous ones. The tide now ran in favor of theheliocentric theory, and from the middle of the seventeenth century there were few important astronomers who were notCopernicans.