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Ptolemy postulates Ptolemaic System. Ptolemy’s system was important because it proposed a fundamental structure to explain the motion of the stars and the heavenly bodies. The Ptolemaic System remained the prevailing theory concerning the universe among many intellectuals and astronomers for over a thousand years until the late Middle Ages.
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Eratosthenes was the first person to accurately measure the size of the Earth as well as the tilt of the Earth. Eratosthenes work was significant because it allowed him to calculate the distance from the earth to the sun.
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Copernicus postulates the Heliocentric theory. This discovery is significant because it controverted the idea that the earth was the center of the universe and everything else in the heavens revolved around the earth.
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Tycho Brahe discovers an usually bright star which turns out to be the first known recorded observation of a supernova. The discovery is considered important because it directly controverted Aristotle’s world view that the heavens beyond the moon are perfect and unchanging.
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Postulated three laws of planetary motion. This theory is significant because unlike the stars, the planets do not move in unchanging, uniform motion, but in motion which goes faster and slower as they orbit the Sun; in motion which almost certainly requires some kind of force, most likely due to the Sun, to keep them moving that way.
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Newton postulates law of gravitation. Newton’s law is significant because it demonstrated that the laws governing astronomical bodies were the same laws governing motion on the surface of the Earth.
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Einstein postulates General Theory of Relativity. This discovery is significant because it demonstrates that Newton was right about most things, but wrong about how gravity affected very large and very distance objects. It's actually two theories - Special Relativity and General Relativity.
