Copernicus

In his most famous book De Revolutionibus, Nicolaus Copernicus argued that the Sun, not the Earth, was the centre of the universe. Printed in 1543, his heliocentric view of the solar system argued against nearly 2000 years of entrenched scientific theory, and proved to be the most important Copernican thesis. As this post will show, the Sun as the centre was a even more revolutionary idea for human comprehension than it was for astronomical precision.

That Copernicus was the first to interpret the universe as revolving around the Sun, or that the Earth spun on its own axis were not brand new ideas. Jean Buridan (c. 1300-1358), Nicole Oresme (c. 1320-1382), and Nicholas of Cusa (1401-1464) were all medieval polymaths who had developed a diurnal conception of the Earth in the fourteenth and fifteenth centuries - before Copernicus's time - and even an ancient Greek astronomer, Herakleides, proposed such a theory. Another, Aristarchus of Samos, also believed in a heliocentric universe and a daily spinning Earth motion. It seemed far more plausible that the tiny Earth, not the gigantic universe around it, could rotate within a 24-hour period. Copernicus is such an influential figure in this field because he was the first to construct "a mathematical system of planetary motion from a heliocentric perspective." Though he (incorrectly) assumed that the Sun was stationary (his protege Johannes Kepler later corrected this view), "Copernicus was the first to develop a detailed account of the astronomical consequences of the Earth's motion." His system provided something that the long traditional Ptolemeic model did not - coherence. With Copernicus's heliocentric model, "the retrograde motions of the (inner and outer) planets become a natural consequence of the motion of the Earth around the (mean) sun" and the motion of the planets was uniform. Here, "Copernicus's solution is only partially successful because he still assumes uniform circular motion" but "the major irregularities of the planetary motions are only apparent. These appearances are produced by the orbital motion of the Earth. As the sun is stationary in the heliocentric system, it does not have retrograde motion" (Weinert, 21-5; Margolis, 87, 106 [note 10]).

Copernicus's model also enabled him to measure the distances between planets. Adopting mathematical methodologies used since antiquity and updated observations of planetary orbits, Copernicus could determine the relative distance of the planets from the Sun and from each other. 

[The Copernican Model of the Solar System; source: Google Images] 

Here again, we see a coherent system that could do away with the antiquated beliefs of celestial spheres. That being said however, Copernicus's observations did not totally disprove the ancient Greek astronomical observations nor, especially, Ptolemy's heavily entrenched geocentric model:

"The Greeks sought to fit the appearances they observed to their prior beliefs about celestial phenomena.

Copernicus claims that his work is based on long and numerous observations, his own and those of the

Greek tradition.... Nevertheless Copernicus's observations do not establish any new facts. The Copernican

observations do not go beyond the discoveries of the Greeks. They do not cast in doubt Greek

presuppositions about circular motion. It is therefore fair to say that from an observational point of view,

the Copernican and Ptolemaic systems were equivalent" (Weinert, 25).

Modern astronomers cannot disregard the observations and theories proposed by the ancient astronomers just because of the updated 'discoveries' of Copernicus, Kepler, and other more recent astronomers. For without Ptolemy's model to establish a 'base theory,' Copernicus could not have expanded upon those ideas and eventually develop his own model.

Explaining the season was another conundrum which the Greeks were aware of, but still required an astronomical model for comprehension. In a geocentric universe, the variations in weather and temperature which corresponded with the four seasons in a year could not be definitively explained. So Ptolemy, using observations by Hipparchus, devised a system with eccentric or displaced circles. At a 23.5 degree angle, the Sun would orbit the Earth on a tilt. Copernicus's model attained a more difficult theory concerning this phenomenon - a third motion, or "deflexion of the Earth's axis." Because the planets lay within celestial spheres (again, disproved by Kepler, who argued that astronomy could do "without the useless furniture of fictitious spheres and circles"), and moved as part of a system, the seasons and the length of days fit a symmetrical pattern (Weinert, 25-8).

Copernicus's theory of a heliocentric universe was fundamental to the establishment of a humanist approach to science. Although humans were no longer the centre of the universe, they could however apply a mathematical and geometrical methodology to rationalising the vast wonders of the cosmos. "By making Earth a planet, Copernicus revolutionized humanity's view of its place in the universe and triggered a controversy that would eventually bring the astronomer Galileo Galilei before the Inquisition."  To arrive at such a conclusion meant the opening of other radical ideas. It signified the beginning of a new scientific paradigm, displacing nearly 2000 years of entrenched astronomical thought. Simon Stevin, William Gilbert, Thomas Digges, Kepler and Galileo were all contemporary astronomers of Copernicus to encourage this new paradigm shift (Weinert, 1, 20; Backman, Seeds, et al, 53-4; Margolis 70]

A mobile Earth could naturally explain retrograde motions, the seasons, and the relative distance of planets from the Sun within a heliocentric universe. Thus, Copernicus's system proved to be another launching pad for further research and quantitative data on our solar system. More importantly, it fundamentally changed the way we humans viewed our place in the universe.

Sources:

Backman, Dana E, Michael A. Seeds, et al. Astro. Toronto: Nelson Education, 2013.

Margolis, Howard. It Started with Copernicus: How Turning the World Inside Out Led to the Scientific Revolution. New York: McGraw-Hill, 2002.

Weinert, Friedel. Copernicus, Darwin, & Freud: Revolutions in the History and Philosophy of Science. Chichester: Wiley-Blackwell, 2009.