Tradition and Faith in the Copernican Revolution 

 Physics Department
 Wheaton College
 Wheaton, Illinois 60187

From: Perspectives on Science and Christian Faith 43 (March 1991): 36-42.

A review of the Copernican revolution reveals the importance of nonempirical factors in its development. The writings of Copernicus, Kepler and Galileo show the continuity of their ideas with the Greek classical tradition and the connection of their work with their Christian faith. These human dimensions illustrate how cultural values, creative insights and personal commitments can be as important in science as empirical evidence. 

The success of Copernicus, Kepler and Galileo in developing a heliocentric system of the planets led eventually to the dominance of empiricism in much of Western thought. Ironically, the champion of this new empirical emphasis, Francis Bacon, rejected the Copernican system nearly a century after it was introduced. He stressed the need to examine the data of experience without allowing any personal bias to shape the organization of facts. Bacon's inductive method seems at odds with the deductive method of Descartes, with its emphasis on rationalism; but both agreed that nature should be interpreted by rejecting the traditions of the past.
An examination of the Copernican Revolution reveals that it was based on a much richer approach to interpretation than the rational empiricism that came to dominate the Enlightenment. Its success depended on such nonempirical interpretative elements as imaginative constructs, aesthetic criteria, and ethical commitments. It borrowed heavily from the Greek classical tradition and found fresh motivations from the attitudes and values fostered by Christian faith.

In the century following Copernicus, astronomers competed over several systems for interpreting the motions of the planets. The geocentric system of Aristotle could account for planetary motions by a system of concentric ethereal spheres to carry the planets. The Aristotelian system was refined by Ptolemy about 150 A.D. by using a combination of circles forming epicycles to describe planetary motion. This Ptolemaic system was complicated, but among its advantages was the fact that it could explain the increased brightness of the planets during retrograde motion since this reversal of direction occurred as the planets moved on that part of the epicycle closest to the earth.

The heliocentric system of Copernicus was more than an alternate interpretation of observed data. It involved a radical new perspective and eventually a change in worldview.1 The Copernican system offered some geometric advantages, but it was not widely accepted for many years because of problems associated with the idea of a moving earth. The Tychonic system was introduced about fifty years after Copernicus and gained a following because it had many of the geometric advantages of the Copernican system, but did not require the motion of the earth. During the sixteenth century these competing systems were based on the same empirical data, but the interpretation of these data differed widely.

The idea of a moving earth was the stimulus for the development of a new scientific worldview, culminating in the Newtonian synthesis, and a new respect for the authority of science. Although science professes to reject authority as a source of knowledge, most educated people believe that the earth moves on the authority of science. Few know the rational arguments in favor of the Copernican theory, or the empirical evidence that supports those arguments. This blind faith in scientific authority extends to many areas of modern life in ways that are hardly matched by any other influences in our past or present culture. The recognition from its history that science depends on more than empirical evidence and rational demonstration points the way toward finding other valid criteria of interpretation in seeking to understand the world. The effect of Copernican astronomy on Biblical interpretation has been considered elsewhere.2 Here, the primary concern will be the role of interpretation in natural science, which will be illustrated from the Copernican Revolution.


The work of Nicolaus Copernicus (1473-1543) had strong elements of continuity with past traditions, even though he rejected the geocentric systems of Aristotle and Ptolemy. The revival of Platonism in Italy during the Renaissance as an alternative to Aristotelian scholasticism provided a new community of interpretation emphasizing the Pythagorean doctrine of mathematical harmony. During some of his ten years in Italy, Copernicus studied astronomy with Domenico di Novara, one of the leaders in the revival of Greek studies, who criticized the Ptolemaic system and emphasized the Pythagorean ideas of geometric harmony and simplicity. In the preface to his 1543 treatise On the Revolutions of the Heavenly Spheres, addressed to His Holiness Pope Paul III, Copernicus quoted from Plutarch to indicate some of the sources of his new system of the world:

 Some say that the Earth is at rest, but Philolaus the Pythagorean says that it is carried in a circle round the fire, slantwise, in the same way as the Sun and Moon. Heraclides of Pontus and Ecphantus the Pythagorean give the Earth motion, not indeed translatory, but like a wheel on its axis, from west to east, about its own centre.3

In his discussion of the motion of the earth he makes a brief mention of the heliocentric hypothesis of Aristarchus of Samos.4 The conservative nature of this treatise is evident in its adherence to the Platonic theory of "uniform circular motion" in the celestial region.5 This required combinations of circles for each planet similar to the epicycles used by Ptolemy. Copernicus rejected the equant, introduced by Ptolemy as a point of reference to obtain uniformity of planetary motion, as an unnecessary irregularity. The heliocentric perspective not only eliminated this irregularity, but it also made possible the calculation of the distance of each planet from the sun, revealing a regular increase in proportion to its period.

The heliocentric interpretation of Copernicus involved an element of commitment to his concept of mathematical harmony that sometimes trans-cended physical reasoning and empirical evidence. In fact, the only physical argument given by Copernicus for the earth's motion was its spherical shape: "For the movement of a sphere is a revolution in a circle, expressing its shape by the very action."6 It was a bold step of faith for Copernicus to transfer this perfect celestial motion of the Aristotelian tradition to the imperfect terrestrial region: "As it has now been shown that the Earth has the shape of a globe, I believe we must consider whether its motion too follows its shape."7 This "belief" contradicted the common sense ideas of motion derived from Aristotle's physical principles, which taught that violent motion in the terrestrial region requires the agency of a mover. Furthermore, from Aristotelian principles a moving earth would quickly outdistance objects dropped at the earth's surface, resulting in an apparent horizontal motion that is clearly contrary to observation.

From Aristotelian principles a moving earth would quickly 
outdistance objects dropped at the earth's surface, 
resulting in an apparent horizontal motion 
that is clearly contrary to observation.

Even apart from Aristotelian physics, the Copernican theory had few empirical advantages and failed to satisfy the crucial empirical test of stellar parallax. His system offered no greater accuracy in predicting planetary positions than the Ptolemaic system. It did give a more natural explanation for the proximity of Mercury and Venus to the sun and for the retrograde motions of the planets; but Copernicus himself recognized the empirical failure of his system to account for the lack of stellar parallax. Thus, if the earth orbits annually around the sun, the directions to the stars (parallactic angles) should change as the earth revolves about an orbital diameter of 186 million miles. Copernicus offered the following argument for this empirical failure:

That there are no such phenomena for the fixed stars proves their immeasurable distance, because of which the outer sphere's (apparent) annual motion or its (parallactic) image is invisible to the eyes... So great is this divine work of the Great and Noble Creator!8

Thus, his interpretive commitment to the earth's motion led him to a greatly expanded view of the universe supported by his faith in the power and majesty of God. The first evidence of stellar parallax was not observed until nearly 300 years later by F.W. Bessel, using telescopic equipment of much greater accuracy.

Copernicus' commitment to a realistic interpretation of the earth's motion was brought into question for several years by an anonymous preface to The Revolutions, apparently added without his approval at the time of its publication in 1543 as he lay dying. Entitled "To the Reader on the Hypotheses in this Work," this preface stated: "Nor is it necessary that these hypotheses be true, nor indeed even probable, but it is sufficient if they merely produce calculations which agree with the observations."9 Such an instrumentalist interpretation seems to misrepresent the intentions of Copernicus, but was probably added to make it more acceptable to possible critics. It was written by the Lutheran Andreas Osiander who had been left in charge of publication arrangements by Joachim Rheticus, also Lutheran. Rheticus had taken leave from the University of Wittenberg in 1539 to study with Copernicus, not without some risk for a Protestant at the time. He published one of the first accounts of the heliocentric system in 1540. The Osiander preface was identified years later by Kepler as a deception.

Brahe and Kepler

Acceptance of the ideas of Copernicus was a slow and gradual process. His mathematical techniques were often used without accepting the mobility of the earth. The greatest observational astronomer before the invention of the telescope, the Danish nobleman Tycho Brahe (1546-1601), rejected the Copernican system, but he did recognize the advantages of heliocentric motion. In 1577 Brahe showed that comets move through the planetary orbits, casting doubt on the medieval idea of crystalline spheres. He greatly improved the accuracy and scope of astronomical observations, but was unable to detect the stellar parallax that would empirically demonstrate the earth's motion. His solution to the problem of planetary motions was a stationary earth with all the planets orbiting the sun as it circled the earth. This Tychonic system was mathematically equivalent to the Copernican system, but avoided the problems of a moving earth. Several natural philosophers, including Francis Bacon, accepted it as a convenient compromise of the more radical Copernican interpretation. It is a good example of the way in which science can be hindered by placing too much emphasis on the limitations of empirical data.

The Tychonic system is a good example of the way 
in which science can be hindered by placing too much emphasis 
on the limitations of empirical data.

Brahe's younger associate during the last year of his life, the German Lutheran Johannes Kepler (1571-1630), had great respect for the accurate data he inherited from Brahe, but none of the empirical inhibitions to prevent him from embracing the Copernican vision. He was introduced into the small community of Copernican interpretation by his astronomy professor, Michael Maestlin, at the Protestant University of Tubingen where he was studying for the clergy. He was strongly motivated by Renaissance Platonism and a desire to discover the architectural design of God's creation. The Copernican geometry provided an unprecedented basis for calculating the distances of the planets relative to the earth's orbital radius, which Kepler attempted to correlate with the geometry of the five regular solids of Pythagoras in his Cosmographic Mystery of 1596. 

In seeking such harmonies, Kepler was motivated by theological 
and aesthetic values in his interpretation of the planets "since God has 
established nothing without geometrical beauty...."

Although much of Kepler's creative interpretation was inspired by Pythagorean concepts of geometry and harmony, he did not allow his presuppositions to suppress empirical data. When his analysis of the orbit of Mars conflicted with Brahe's measurements, he abandoned the Platonic tradition of circular orbits, even though their deviation from the measured positions was only detectable because of the improvement of Brahe's new data over Greek observations. He discovered that elliptical orbits (now known as Kepler's first law) did fit the data. This law was augmented by his second law describing planetary speeds by equal areas swept out in equal times about the sun, which for Kepler symbolized God's rule over His creation. These laws eliminated the need for complicated combinations of circles, and introduced a new level of geometric simplicity to the heliocentric system. In seeking such harmonies, Kepler was motivated by theological and aesthetic values in his interpretation of the planets "since God has established nothing without geometrical beauty...."10

Kepler's incredible efforts to understand and interpret planetary motion were sustained by his faith in the order of God's creation and the Biblical conviction that it was intelligible to those created in His image. He offers this response to news of Galileo's telescope:

All that is overhead, the mighty orbs
With all their motions, thou dost subjugate
To man's intelligence.11

Kepler's incredible efforts to interpret planetary motion 
were sustained by his faith in the order of God's creation 
and the Biblical conviction that it was intelligible to those created in His image.

His third law of the planets relating their distances and periods about the sun was a by-product of an extended analysis based on musical harmony. This result eventually became a key element in establishing Newton's law of universal gravitation as a unified physical basis for the Copernican system. Kepler's faith in the reality and simplicity of the Copernican system led him to discover new mathematical harmonies in its structure based on Brahe's data, in spite of the unresolved problems of a lack of stellar parallax and an inadequate physical basis for the earth's motion. In the conclusion of his Harmony of the World, published in 1619, Kepler gave expression to the religious foundation of his radical interpretation of the celestial world:

Great is the Lord and great His virtue
and of His wisdom there is no number:
praise Him, ye heavens,
praise Him ye sun, moon, and planets,
use every sense for perceiving,
every tongue for declaring your Creator.
Praise Him, ye celestial harmonies,
praise Him, ye judges of harmonies uncovered:

and thou my soul, praise the Lord thy Creator...12


In his support of Copernicus, Kepler was joined by Galileo Galilei (1564-1642), his Italian contemporary and sometime correspondent. Galileo's use of the telescope and his study of motion were vigorously applied to the defeat of Aristotelian science and arguments in favor of the heliocentric system. His efforts also reveal an interesting mixture of traditional and radical elements of interpretation that often went beyond the empirical evidence he discovered. Although Galileo rejected the more mystical aspects of Kepler's Pythagoreanism, he shared the Platonic emphasis on geometry strengthened by his great admiration for the mathematical works of Archimedes, which became available in printed form in 1543 about the time Copernicus died. Galileo's major publications were written in the form of a Platonic dialogue, with Salviati expressing his opinion:

That the Pythagoreans held the science of numbers in high esteem, and that Plato himself admired the human understanding and believed it to partake of divinity simply because it understood the nature of numbers, I know very well; nor am I far from being of the same opinion.13

Galileo's Christian faith reinforced this view:

...the great book of the creation of the omnipotent Craftsman, and is accordingly excellently proportioned, nevertheless that part is most suitable and most worthy which makes His work and His craftsmanship most evident to our view.14

In some ways Galileo maintained a more traditional interpretation 
of the planets than Kepler, refusing even to accept Kepler's 
elliptical orbits in place of the perfection of celestial circles.

In some ways Galileo maintained a more traditional interpretation of the planets than Kepler, refusing even to accept Kepler's elliptical orbits in place of the perfection of celestial circles. In attempting to develop a physical basis for the motion of the earth and the tendency of falling objects to move with the earth, even his concept of inertia is defended as a form of circular motion:

But motion in a horizontal line which is tilted neither up nor down is circular motion about the center; therefore circular motion is never acquired naturally without straight motion to precede it; but, being once acquired, it will continue perpetually with uniform velocity.15

This inertia concept borrowed heavily from the impetus theory of the fourteenth century nominalist tradition of Jean Buridan and Nicole Oresme of the University of Paris. Eventually the concept of inertia was generalized to straight-line motion by Descartes and became the first of Newton's axioms of motion. Thus, the interpretive assumption that the natural state of a moving object was to remain in motion with a constant velocity became the basis for a consistent Copernican cosmology, replacing the Aristotelian idea that motion requires a mover.
Galileo's most convincing efforts to establish the Copernican system were related to his pioneering telescopic observations. But even these results required a great deal of interpretation and were not completely adequate to verify the heliocentric theory. Galileo acknowledged that his scholastic critics held the view that operations with the telescope were "considered as fallacies and deceptions of the lenses."16 His observations of lunar craters and sun spots were interpreted as celestial imperfections and therefore damaging to the Aristotelian doctrine of the perfection and incorruptibility of the heavens. The discovery of four celestial objects adjacent to Jupiter but with a shifting alignment were interpreted as moons circling Jupiter, thus providing a counter example to geocentric motion. Perhaps the most important telescopic discovery of Galileo was his observation of the phases of Venus changing in a complete cycle like the moon, which could be explained by the Copernican system but not by the Ptolemaic system. However, this could also be explained by the Tychonic system, which was conveniently ignored by Galileo.

The final acceptance of the heliocentric system came 
after the Newtonian synthesis provided a complete physical explanation 
for the motion of the earth and the planets, held in their 
orbits by universal gravitation.

Thus, Galileo's interpretations cast doubts on Aristotelian cosmology and Ptolemaic astronomy, but the evidence was still insufficient to establish the heliocentric system. In discussing stellar parallax as missing evidence for the earth's motion, he suggests that it had not been observed due to lack of precision, "both on account of the imperfection of astronomical instruments, which are subject to much variation, and because of the shortcomings of those who handle them with less care than is required."17 The final acceptance of the heliocentric system came after the Newtonian synthesis provided a complete physical explanation for the motion of the earth and the planets, held in their orbits by universal gravitation. This provided a unified interpretation of all motions on earth and in the heavens, refining Galileo's laws of terrestrial motion and Kepler's laws of celestial motion, even though another 150 years were required for direct evidence of the earth's motion from measurements of stellar parallax.

Summary and Conclusions

The Copernican Revolution reveals a richness of interpretation that goes beyond the typical view of scientific empiricism. Science, like literature, theology, or other forms of human understanding, depends on past traditions, cultural values, communal relations, imaginative speculations, aesthetic considerations, and ethical commitments, as well as empirical evidence. Indeed, these additional criteria of interpretation are often the key to success in science. It will be instructive to conclude with a brief review of the role of historical traditions, communal values, creative insights and personal commitments in scientific interpretation during the Copernican Revolution.

Continuity with past traditions is evident in varying degrees in the work of Copernicus, Kepler, and Galileo, even though much of their effort marked a break with the Aristotelian tradition. They were especially influenced by the mathematical concepts of the Pythagoreans and the philosophical ideas of Plato. Even Brahe's greater empirical emphasis led to an interpretation of the planets based on the Platonic assumption of uniform circular motion in his Tychonic system. The Alexandrian Greek tradition also provided alternatives to Aristotelian scholasticism, especially in the work of Aristarchus and Archimedes. Galileo also benefited from the fourteenth-century nominalist reaction against the original Aristotelian doctrine of violent motion, and from the resulting impetus concepts of Buridan and Oresme.

Instead of faltering over the lack of stellar parallax 
or decrying the displacement of human centrality in the universe, 
they imagined an expanded universe matching the power and glory of God.

Community sources of interpretation helped to advance the gradual development of the Copernican Revolution by providing mutual support and the reinforcement of new cultural values. Copernicus was aided by men like Rheticus, while Kepler was encouraged by correspondence with Galileo, who was supported by a circle of like-minded students. The revival of Greek classics and the renewed interest in Platonism in the fifteenth century opened up the new emphasis on mathematical harmony, simplicity, and order in the sixteenth century. These new ideas were reinforced and expanded by the context of new Christian attitudes and values that had emerged in the preceding centuries. Many of these values were supported by the Church in spite of their opposition to heliocentrism. Platonic thought emphasized the application of mathematics primarily to the celestial realm of perfection. In contrast, the Biblical view of creation with its emphasis on the goodness of all that God made, along with the Christian doctrine of the incarnation, introduced a new appreciation for material reality and order in the terrestrial world. This is evident in the Franciscan celebration of all of God's creatures and the nominalist interest in the detailed particulars of creation. 

The ethical norm of commitment demands responsible efforts, 
including a willingness to reconsider a theory in the light of new evidence 
or criticisms leveled by other scientists.

Creativity was one of the strongest features of the Copernican interpretation, transcending its empirical and physical limitations. Instead of faltering over the lack of stellar parallax or decrying the displacement of human centrality in the universe, they imagined an expanded universe matching the power and glory of God. Instead of accepting the constraints of an imperfect terrestrial world bound within the perfect celestial spheres, they saw the motion of the earth as the basis for unifying physical laws and demystifying the heavens in a universe created and sustained by One God. Creative imagination is especially evident in Kepler's vivid use of geometric, musical, and spiritual analogies to discover new levels of order among the planets. The Renaissance and Reformation produced new confidence in the intelligibility of the world and its status as a revelation open to creative interpretation.

Commitment to the reality and harmony of the Copernican universe is evident in the persistent efforts required to establish it in the face of scientific objections and scholastic opposition. A kind of mental conversion was required to see old information from a new perspective. Personal commitment to this new worldview was necessary to sustain a lifetime of active effort to work out its implications during the decades of its conflict with accepted ideas. Commitment to a theory is a necessary ethical norm if a scientist expects to be trusted by fellow scientists that evidence for a theory is considered adequate and consistent. The ethical norm of commitment demands responsible efforts, including a willingness to reconsider a theory in the light of new evidence or criticisms leveled by other scientists. In the Copernican Revolution this commitment was accompanied by a strength of conviction and religious zeal not always associated with scientific interpretation. But it reveals the human dimensions of science that serve as a warning against the temptation to worship scientific authority.


1Thomas S. Kuhn, The Structure of Scientific Revolutions (Chicago: The University of Chicago Press, 1970), pp. 111-135.
2William Hine, "Copernican Astronomy and Biblical Interpretation," Christian Scholar's Review, III: 2 (1973), pp. 134-149.
3Copernicus, On the Revolutions of the Heavenly Spheres, trans. A. M. Duncan (New York: Barnes and Noble, 1976), p. 26.
4Ibid., p. 53.
5Plato, "The Timaeus," in Timaeus and Critias, trans. Desmond Lee (Baltimore: Penquin, 1974), p. 45.
6On the Revolutions of the Heavenly Spheres, p. 38.
7Ibid., p. 40, emphasis added.
8As cited in Thomas S. Kuhn, The Copernican Revolution (Cambridge: Harvard University Press, 1957), p. 179.
9 p. 22.
10Kepler, The Harmonies of the World, in Great Books of the Western World, Vol. 16, ed. Robert Hutchins, trans. Charles Glenn Wallis (Chicago: Encyclopedia Britannica, 1952), p. 1025.
11Kepler, Dioptrics, as cited in L. Pearce Williams and Henry John Steffens, The History of Science in Western Civilization, Vol. II (Washington D.C.: University Press of America, 1978), p. 172.
12The Harmonies of the World, p. 1085.
13Galileo Galilei, Dialogue Concerning the Two Chief World Systems, trans. Stillman Drake (Berkeley: University of California, 1962), p. 11.
Ibid., p. 3.
15Ibid., p. 28. 
16Ibid., p. 336.
17Ibid., p. 387.