The earliest astronomers were Ptolemy (90-168 AD) and Brahmagupta (590-678 AD). Ptolemy extended the observations and conclusions of Hipparchus, to form his geocentric theory, which is popularly known as the Ptolemaic system. He described his geocentric system and gave various arguments to prove that, in its position at the center of the universe, the Earth must be immovable. Ptolemy argued that since all bodies fall to the center of the universe, the Earth must be fixed there at the center, otherwise falling objects would not be seen to drop toward the center of the Earth.

In Brahmagupta's book, Brahma- sphuta- siddhanta (The Opening of the Univers

In early 1905, Albert Einstein developed a theory based on two assumptions: the principle of relativity, that physical laws are the same in all inertial reference systems, and the principle of the invariance of the speed of light, that the speed of light in a vacuum is a universal constant. He was able to provide a consistent and correct description of physical events in different inertial frames of reference without making special assumptions about the nature of matter, radiation, or their interaction. He accounted for previously unexplained variations in the orbital motion of the planets and predicted the bending of starlight in the vicinity of a massive body such as the sun. The confirmation of this prediction during a solar eclipse in 1919 became a media event, and Einstein's fame spread worldwide.

Galileo was an Italian physicist and astronomer, who, with German astronomer Kepler, started the scientific revolution. His most valuable scientific contribution was his founding of physics on precise measurements instead of using metaphysical principles and formal logic. In late 1609, he had built a telescope of 20 times magnification, with which he observed the mountains and craters on Earth's moon. He also saw that the Milky Way was composed of stars, and he discovered the four largest satellites of Jupiter. By 1610, he had observed the phases of Venus, which proved the Copernican system, that the Earth revolved around the sun, and disproved the Aristotelian and Ptolemaic assumptions that the planets circled a fixed Earth.

Kepler formulated and verified three laws of planetary motion, now known as Kepler's laws. Under the basis of the Copernican Theory, he produced a hypothesis to account for distances between planetary orbits. In 1609, he published a thesis containing statements of two of his laws of planetary motion: that planets move in ellipses, and that planets move faster as they near th

Some common words found in the essay are:
Copernican Theory, Albert Einstein, Issac Newton, Galileo Italian, AD Ptolemy, Copernicus Polish, Earth Brahmagupta's, , Tycho Brahe's, Quoting Brahmagupta, solar system, center universe, planetary motion, laws planetary motion, laws planetary, earth center universe, universe earth, planets move, center universe earth, earth center, planetary orbits, venus mars, 365 days 6, formulate laws, planets move faster,
Approximate Word count = 1292
Approximate Pages = 5 (250 words per page double spaced)