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He was the one that proposed the idea that the Earth is the centre of the universe and that all the planets and stars are orbiting our planet.
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He discovered that the planets revolved around the Sun rather than the Earth.
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He discovered that planets do not orbit the Sun in perfect circles, and that they were ellipses.
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He improved the telescope, which lead him to discover the four moons of Jupiter.
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He predicted the orbit of Halley's comet by recording the comet sightings in the past hundred years.
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He discovered the planet Uranus after observing the sky through his telescope. He also discovered several moons around gas giants a few years later.
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The first asteroid, Ceres was discovered on 1801 by Giuseppe Piazzi. The second asteroid, Pallas, was discovered on 1802 by Heinrich William Matthias olbers who also discovered the Vesta on 1807. The third asteroid was discovered by Karl Ludwig Harding on 1804, named Juno.
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He predicted the existence of Neptune by using mathematics.
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He discovered the dwarf planet, Pluto.
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They were sent out into space the collect information on planets.