The Ptolemaic model was accepted by most philosophers of note until it was radically challenged by the Polish astronomer Copernicus in 1530. The Catholic church condemned the Copernican System in 1616 and forbade holding, defending, or even teaching alternatives to the Ptolemaic conception of the universe endorsed by the Church (Fowler 2008:10). But both theories were mere conjecture until the development of the Galilean telescope. Galileo's telescope was a modification of the currently existing lenses used for reading by the long -- and short-sighted. Galileo did not invent corrective lenses or even the telescope, but he did substantially improve them. By making use of both convex and concave lenses, Galileo was able to expand the magnification power and distance vision of ordinary gazers, enabling to look wide into the heavens (Fowler 2008:10). "Galileo's belief that his discoveries with the telescope strongly favored the Copernican world view meant he was headed for trouble with the Church" (Fowler 2008:10). As illustrated in Two Pieces of Glass, a critical aspect of Galilean theory was the presence of sunspots, or dark patches on the surface of the sun. "He observed," through the use of his telescope, "motion of the sunspots indicating that the Sun was rotating on an axis. These blemishes on the Sun were contrary to the doctrine of an unchanging perfect substance in the heavens, and the rotation of the Sun made it less strange that the Earth might rotate on an axis too, as required in the Copernican model. Both represented new facts that were unknown to Aristotle and Ptolemy" (Galileo: The telescope and laws of dynamics, 2010, Astronomy 161).

Other critical findings of Galileo were the presence of moons orbiting around Jupiter, and evidence that "Venus went through a complete set of phases, just like the Moon. This observation was among the most important in human history, for it provided the first conclusive...

Other discoveries included the rings of Saturn; that the planets were disc-shaped, not points of light; the 'cloud' of stars now known as the Milky Way and the fact that the moon was covered by a series of craters and not smooth (Galileo: The telescope and laws of dynamics, 2010, Astronomy 161).
All of these physical findings were unknown to the Greeks, and indeed could not have been known to the Greeks because of the limits of their technology. However, Galileo's achievement was not merely technical, in terms of his improvement of existing telescopic technology. It was also profoundly important in the way that it approached the natural world. Creating a coherent philosophical and religious system and making sense of man's relationship to the cosmos was of less importance than truly understanding how things 'worked.' Galileo's rigor and mathematical precision set the tone for modern science in all disciplines and continues to do so to this day. Although some of the early Greek philosophers did prefigure the Galilean approach, Galileo's marriage of hands-on work, observation, and empirical as well as deductive intelligence was unique and truly changed the way human beings saw the world.

References

Fowler, Michael. (2008, August 23). Galileo & Einstein. University of Virginia Physics.

Retrieved February 11, 2011 at http://galileoandeinstein.physics.virginia.edu/lectures/lecturelist.html

Galileo: The telescope and laws of dynamics. (2010). Astronomy 161.

Retrieved February 11, 2011 at http://csep10.phys.utk.edu/astr161/lect/history/galileo.html

Sobel, Dana. (2002). Galileo's battle for the heavens. Nova. Retrieved February 11, 2011 at http://www.pbs.org/wgbh/nova/galileo/science.html