Nicolaus Copernicus

Polish astronomer Nicolaus Copernicus is considered as a pivotal figure in the history of astronomy and physics. Departing from the prevailing notions about a geocentric universe, he covincingly proved the helio centric model. Coppernicus proposed that the planets have the Sun as the fixed point to which their motions are to be referred; that the Earth is a planet which, besides orbiting the Sun annually, also turns once daily on its own axis; and that very slow, long-term changes in the direction of this axis account for the precession of the equinoxes. This representation of the heavens is usually called the heliocentric, or “Sun-centred,” system.” The book that contains the final version of his theory, De revolutionibus orbium coelestium libri vi (“Six Books Concerning the Revolutions of the Heavenly Orbs”), appeared in print in 1543, the year of his death. Copernicus postulated that, if the Sun is assumed to be at rest and if the 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 (225days), Earth (1 year), Mars (1.9 years), Jupiter (12 years), and Saturn (30 years). To accept the theory’s premises, one had to abandon much of Aristotelian natural philosophy and develop a new explanation for why heavy bodies fall to a moving Earth.