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he thought the sun,stars, planets revolve around the earth.
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he came up with the helocentric theory
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improved the telescope venus has phases like the moon . he also dicoved the milky way.
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the orbit of a planet about the sun is an eclipse with suns center mass at one focus. using a model he made
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he belived in gravity because he tested 2 different objects dropped will hit the ground at the same time.