A: Nicholas Copernicus

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.