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THE CLASSICAL THEORIES
The Geocentric System comes from the Greek word “geo,” which means “earth.” The Greek philosopher Ptolemy originally came up with the Geocentric System (see above left) of how our planets are aligned with one another.
The ancient Chinese had slightly different astronomical variants. The most archaic Chinese cosmological model, Gai Tian (top right), consists of a flat earth and umbrella-like heavens, whereas its centuries-long opponent, Hun Tian (above right) model, was presented through the analogy of "egg" The flat earth was situated in the middle of the egg yolk and surrounded by water, while the heavens were like the egg shell.
Nicholas Copernicus was a famous scientist who figured out that the earth completes one revolution on its axis daily and traveled around the sun once a year. He refuted the idea of the Geocentric System with a theory of his own, called the Heliocentric system. The word “helio” means “sun.” Copernicus expressed these revolutionary ideas in his book, On the Revolutions of the Heavenly Bodies, which was published in 1543 (after his death) and dedicated to the pope. Copernicus postulated that, if the Sun is assumed to be at rest and if Earth is assumed to be in motion, then the remaining planets fall into an orderly relationship whereby their sidereal periods increase from the Sun as follows: Mercury (88 days), Venus (225 days), Earth (1 year), Mars (1.9 years), Jupiter (12 years), and Saturn (30 years). From a modern point of view, the Copernican model has a number of advantages. Copernicus gave a clear account of the cause of the seasons: that the Earth's axis is not perpendicular to the plane of its orbit.
Danish astronomer Tycho Brahe (pictured left) had a flamboyant lifestyle (his silver nose prosthetic from a duel over who was the better mathematician) and an ignominious death (held his urine too long at a banquet? poisoned by his assistant? bladder infection?). In 1572, Brahe observed a supernova in the constellation of Cassiopeia. Upon learning that Tycho intended to leave Denmark [in 1575] in order to pursue his interests in studying the universe, King Frederick granted him the island of Hven, and helped finance the building of his observatory there. At his observatory, Brahe kept meticulous observations of the heavens. While most astronomers only focused on observing heavenly bodies at specific, unusual points in their orbits, Brahe intently tracked them in their entire visible orbit across the sky, creating the most precise observations made at the time. Some of his measurements were accurate to half an arc minute, which is especially admirable given that they were all made before the advent of the telescope. In addition to his observations, he also designed and built instruments, periodically calibrating them and checking their accuracy.
René Descartes was extensively educated, first at a Jesuit college established by the king of France, the at age 8, then earning a law degree at 22. But an influential teacher set him on a course to apply mathematics and logic to understanding the natural world.
Descartes is considered by many to be the father of modern philosophy, because his ideas departed widely from current understanding in the early 17th century, which was more feeling-based. While elements of his philosophy weren’t completely new, his approach to them was. Descartes believed in basically clearing everything off the table, all preconceived and inherited notions, and starting fresh, putting back one by one the things that were certain, which for him began with the statement “I exist.” From this sprang his most famous quote: “I think; therefore I am.”
He introduced Cartesian geometry, which incorporates algebra; through his laws of refraction, he developed an empirical understanding of rainbows; and he proposed a naturalistic account of the formation of the solar system.
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