Galileo Galilei was an Italian scientist whose inventions and work did much to Renaissance thought in Europe. He is most famous for his work on creating a telescope that was usable for astronomical purposes and for his contention that the solar system centered around the Sun rather than the Earth.
Historically (as opposed to scientifically) speaking, Galileo is most important for the fact that he was one of the first to challenge the Church and other accepted authorities and to, instead, try to find truth through observation. This was an important change because it marked a move toward a way of thinking that was based on science and on observable proof. This new way of thinking was to change the world, helping to bring about such things as the Age of Exploration and even, eventually, the Industrial Revolution.
Galileo, then, is important both for his specific discoveries and for his contributions to changing dominant ways of thought in Europe.
Galileo was an Italian mathematician and astronomer who first used the telescope to observe the night sky. He was a vocal advocate of the Copernicus’ theory that the Earth revolved around the sun. The Catholic Church’s accepted theory was the Ptolemaic model which was the belief that the Earth was a fixed point and other celestial bodies orbited around the Earth. He was advised by the Church that he should not teach or promote the Copernican theory. The Church put Galileo on trial for heresy and he was imprisoned for the remainder of his life for this scientific convictions.