In the world of astronomy, a great debate was raging between the ancient system of Ptolemy, which placed the earth in the center of the universe, and heliocentric system of Copernicus, which posited the sun at the center, and the earth in an orbit around it. In 1609, after word came from Holland of the invention of the telescope, Galileo built his own version of the instrument. With this new tool, he observed the mountains and craters on earth's moon, and discovered four moons orbiting Jupiter. In 1610 he published Sidereus Nuncius, cataloguing his discoveries, and the book made him a celebrity in Europe.Using new evidence provided by his telescope, Galileo now began to advocate strongly the Copernican theory. The Catholic Church, however, disapproved of heliocentricity,
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