On the Revolutions of the Heavenly Bodies - Essay Example

The planets appear to be varying in brightness since they are not always at the same distance from the earth
Earth Centered Universe
The earth-centered universe was proposed by ancient Greek philosophers, Aristotle and Ptolemy. All heavenly bodies are attached to 56 concentric spheres which rotate around the Earth. In their superseded theory of the geocentric model, they assumed that the earth is at the center of the universe and that all planets and stars like the sun revolve around the earth. The Greeks also believed that the motion of the planets was circular and not elliptical. They also believed that the stars were circling the poles and the stars near the equator rising and setting each day and circling back to their rising point.

Polish astronomer Nicolas Copernicus was the first who put forward the sun-centered universe theory which is known as a heliocentric theory in 1514. This theory assumes the sun is at the center of the universe and all other planets revolve around it except the moon. He was successful in predicting the earth’s third place in the solar system. He also believed that the shape of the orbit in which the planets revolve around the sun is not exactly circular. “Sometimes Mars went forward, other times it slowed down or went backward. If the planets all revolved around the Earth, why didn't Mars orbit in a uniform way?” (Dean Regas) This idea questioned the authenticity of the earth-centered universe model and encouraged Copernicus to formulate his famous heliocentric theory.

Earth Centered Universe
The earth-centered universe concept was an ancient theory formulated mainly by some Greek philosophers like Aristotle, Ptolemy, Plato, etc. Observations seem to reinforce this view. The Sun rises in the east and sets in the west. Stars in the north spin counterclockwise around the North Star. And the Earth appears to be the only thing that doesn't move. (Dean Regas) They argued that if the earth did move, then one should be able to observe the shifting of the fixed stars and the shapes of the constellations should be changed considerably over a year. Because of the unawareness about stellar parallax at that time, the Greeks believed that either the earth is not moving or the stars are so far away from us. Their belief was further strengthened by the fact that Venus stays at the same brightness level, all the time which is more consistent with geo-centrism than helio-centrism. (Geocentric model) Read More