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Copernicus's theory “attributed to the earth a daily motion around its own axis and a yearly motion around the stationary sun.”
He followed Nicholas of Cusa in advancing an idea that had far-reaching implications for modern science. Henceforth, the earth could no longer be considered the center of the cosmos; rather it was one celestial body among many, its orbit subject to mathematical prediction.

Professor Zinner did not know of Guo Shoujing's work. In my submission, we can go further. Did Copernicus directly copy Regiomontanus in proposing his revolutionary theory that the earth and the planets circled the sun and that the sun, not the earth, was at the center of the solar system?

I say he did, and I base my argument on the research of Noel M. Swerdlow, assistant professor of history at the University of Chicago, presented in “The Derivation and First Draft of Copernicus' Planetary Theory”
¹⁹

In his tightly reasoned article, Professor Swerdlow starts with an interesting comment Copernicus made to the pope at the time he published his revolutionary work,
De revolutionibus orbium coelestieum
, in 1543. Copernicus told Pope Paul III of his great reluctance to publish this theory—that the earth was not the center of the cosmos but one celestial body among many—for fear of ridicule by the public. He explained that he had been reluctant “not for just nine years but already in the fourth nine year period—that is,” since about 1504, a time after Copernicus had obtained Regiomontanus's
Ephemeris
and
Epitome
in Bologna.

Between 1510 and 1514 Copernicus summarized his new ideas in
De hypothesibus motuum coelestium e se constitutis commentariolus
(A commentary on the theories of the motions of heavenly objects from their arrangements). Its main parts, to quote the
New Encyclopaedia Britannica,
were “the apparent daily motion of the stars, the annual motion of the sun, and the retrogressive behaviour of the planets results from the earth's daily rotation on its axis and yearly revolution around the sun, which is stationary at the centre of the planetary system. The earth therefore is not the centre of the universe but only of the moon's orbit.”

To quote Professor Swerdlow, Copernicus, in his
De commentariolus,
says next to nothing about how he arrived at his new theories. He begins with a single principle governing planetary theory, and then raises objections to the theories of his predecessors. Next he explains that he has evolved a planetary theory in conformity with his first principles, and this is followed by a set of seven postulates. These have almost nothing to do with either the principle or the objections, but instead assert the surprising theory that the earth and planets revolve around the sun and give some further consequences of this theory.
²⁰

Professor Swerdlow continues:

The sources of Copernicus' early planetary theory are relatively few. The derivation for the models for both first and second anomalies and almost the entire contents of the commentariolus seem to depend on three certain and two possible sources. They are the following:

So there we have it—in Professor Swerdlow's opinion Copernicus followed book 11 of Regiomontanus's
Epitome,
which contained the analysis leading to Copernicus's revolutionary theory.

To quote again from the
New Encyclopedia Britannica
:

Is it rightly called? Or should it be the Regiomontanus or Guo Shoujing revolution?

Johannes Kepler (1571–1630)

Johannes Kepler is today best known for his three laws of planetary motion. His first law stated that the planets traveled around the sun in elliptical orbits with the sun positioned at one of the ellipse's focal points (Nicholas of Cusa's argument, save for focal point). His second law (which he discussed first) stated that the planets swept out equal areas of their orbits in equal times. He rejected the ancient belief that the planets traveled a circular orbit at constant speed, replacing it with the theory that planets' speeds varied with their distance from the sun—fastest when closest to the sun and slowest when farther away—nothing different from what Guo Shoujing had discovered three centuries earlier about planet Earth.
²²

Kepler had learned Copernican astronomy from Michael Mästlin (1550–1631) when he entered the STIFT, the theological seminary of the University of Tübingen, where he was awarded his master's degree in 1591. He published a textbook of Copernican astronomy written in a question-and-answer form, the
Epitome astronomiae Copernicanae.
In my submission, although Kepler may not have appreciated this, he built on Copernican astronomy, which itself derived from Regiomontanus and Nicholas of Cusa, who obtained their fundamental new ideas from Toscanelli and the Chinese astronomical calendar.

Galileo Galilei

Galileo was born in Pisa in 1564. His father was a musician. He was educated at the University of Vallombrosa near Florence; then in 1581 he enrolled at the University of Pisa to study medicine. He never trained as a mathematician or astronomer.

Galileo's life was dominated by the Copernican revolution. He was the first European to develop a powerful telescope with thirty-two times magnification—a huge advance in astronomical observation. He discovered Jupiter's moons, Saturn, sunspots, and the phases of Venus, publishing his results in
Siderius nuncius
(Starry messenger).
²³
This led him to believe Copernican theory was correct; now the trouble started.

The old guard, who had spent their lives teaching Ptolemy's theory that the earth was at the center of the universe, felt their livelihood and reputations threatened. They ganged up on Galileo, gathering support from the Dominicans for his blasphemy in stating that man, God's creation, was not at the center of the universe. The intellectuals and religious fanatics won the day—Copernicus's theory was denounced as “false and erroneous,” and by a decree of March 5, 1616, Copernicus's book was suspended. The chief theologian of the Catholic Church, Cardinal Bellarmine, informed Galileo that he must no longer defend Copernicus. Eight years later, Galileo made an attempt to have the 1616 decree lifted. He did get a small waiver—he was entitled to discuss Ptolemy's and Copernicus's theories provided his conclusion was as dictated by the Catholic Church—which was that man cannot presume to know how the world is made because to do so would restrict God's omniscience.

Galileo accepted this restriction and spent the next eight years writing a dialogue comparing the two principal systems—of Ptolomy and Copernicus. The book was hugely popular—a best seller. The Jesuits seemed defeated but they fought back. Galileo's book was so powerfully written it would cause more harm to the establishment view of the cosmos “than Luther and Calvin put together.”
²⁴

The pope ordered a prosecution. This gave the papal lawyers a big legal problem, for Galileo had abided by the decree of 1616. Suddenly a document was “discovered” to the effect that Galileo in the negotiations leading to the degree of 1616 had been prohibited from “teaching or discussing Copernicanism in any way.” He had therefore obtained the decree by false pretenses because his book was disguised discussion and teaching. The establishment mounted a show trial, which took place in 1633 when Galileo was in his seventieth year and ill. He was
convicted, but his imprisonment was commuted. He was ordered to recant Copernican theory and state that he “abjured cursed and detested” his past errors in supporting Copernicus. While under house arrest he wrote some of his greatest works, summarizing his early experiments. His last big discovery, of the moon's daily and monthly movement, came in 1637, just before he went blind. He died in 1642.

Galileo's monumental achievements were essentially the use of a powerful telescope to discover the heavens and validate Copernicus's work and his pioneering thoughts on gravity. He was the first European who could see that mathematics and physics were part of the same subject and that earthly and heavenly phenomena could be combined into one branch of science, as could experiments with calculation, the concrete and the abstract. Galileo paved the way for Newton.

Galileo is credited with discovering Jupiter's moons, Io, Europa, Callisto, and Ganymede, in 1616. Some scholars contend that the German astronomer Simon Mayer discovered them a few days earlier. In “Ancient Chinese Astronomer Gan De Discovered Jupiter's Satellites 2000 Years Earlier than Galileo,” Paul Dong, Rosa Mui, and Zhou Xin Yan cite Professor Xi Zezong of the Chinese Academy of Sciences, stating that a Chinese astronomer, Gan De, had discovered Jupiter's moons in 364
B.C.
²⁵
The basis for this claim can be found in volume 23 of the ancient Chinese astronomical work
Kai Yuan Zhan Jing
(Books of observations from the beginning of history). A passage in it reads, “Gan De said ‘In the year of Shau Yo, Xi, Nu, Shu and Wei [Io, Europa, Ganymede, and Callisto] the Annual star was very large and bright. It seemed there was a small red star attached to it side. This is called an alliance.'”

The “annual star” was the ancient Chinese name for Jupiter, the small red star, Jupiter's moon. The authors offer a modern translation of Gan De: “There was a small pink star beside the planet Jupiter. We therefore conclude this is a satellite of Jupiter.” (It is still possible today to view Jupiter's satellites with the naked eye in certain places, notably in the Hebei Province of China and from the Sahara and parts of Japan.)

My intention in citing the Chinese observation of Jupiter's moons two thousand years earlier is not to diminish Galileo's enormous achievements but to illustrate how Eurocentric Western historians and
astronomers are in not crediting China with astronomy vastly more advanced than Europe's. It seems almost incredible that the Jesuits could have persuaded the Chinese that they knew more about astronomy than the Chinese did, not least in predicting eclipses, something the Chinese had been doing centuries before Jesuits arrived in China.

The Development of Art and Perspective

Leon Battista Alberti, as Pope Eugenius's notary, would have recorded minutes of the meeting between the Chinese ambassador and the pope. As Joan Gadol has so succinctly said, Alberti went beyond the bounds of astronomy to determine its relation with mathematics, and then [used] mathematics to develop painting and architecture, cartography and surveying—even engineering designs and cryptography. Toscanelli, Alberti, Nicholas of Cusa, Regiomontanus, and later Copernicus and Galileo employed the rational conception of space in forming their ideas—a conception to which all were led by the methods of mathematics.
²⁶