Copernican heliocentrism is the name given to the astronomical model developed by Nicolaus Copernicus and published in 1543. This model positioned the Sun at the center of the Universe, motionless, with Earth and the other planets orbiting around it in circular paths, modified by epicycles, and at uniform speeds. The Copernican model displaced the geocentric model of Ptolemy that had prevailed for centuries, which had placed Earth at the center of the Universe. Copernican heliocentrism is often regarded[by whom?] as the launching point to modern astronomy and the Scientific Revolution.
Heliocentric model from Nicolaus Copernicus' De revolutionibus orbium coelestium (On the Revolutions of the Heavenly Spheres) Although he had circulated an outline of his own heliocentric theory to colleagues sometime before 1514, he did not decide to publish it until he was urged to do so late in his life by his pupil Rheticus. Copernicus's challenge was to present a practical alternative to the Ptolemaic model by more elegantly and accurately determining the length of a solar year while preserving the metaphysical implications of a mathematically ordered cosmos. Thus, his heliocentric model retained several of the Ptolemaic elements, causing inaccuracies such as the planets' circular orbits, epicycles, and uniform speeds,[1] while at the same time introducing such innovative ideas as:-
The Earth is one of several planets revolving around a stationary sun in a determined order. The Earth has three motions: daily rotation, annual revolution, and annual tilting of its axis. Retrograde motion of the planets is explained by the Earth's motion. The distance from the Earth to the Sun is small compared to the distance from the Sun to the stars.
Vietnamization of the war was the U.S. policy that required "South Vietnamese troops to replace American troops". The point of this was to ease frustration in the US that too many American soldiers were dying in a way many Americans felt was pointless.
In his speech, President Obama said that poverty and hopelessness do not cause terrorism, but they cause resentment that terrorist groups use to recruit people. He also says that when governments deny human rights to people, or when their governments treat them like terrorists, people might turn to terrorist groups.
