Copernicus
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Nicolaus Copernicus challenged the geocentric ideas. He proposed a sun-centered, or heliocentric, model of the solar system. The earth and the other planets revolved around the sun. He also proposed that all planets orbit in the same direction but each moves at a different speed and distance from the sun.
Galileo
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Galileo Galilei confirmed Copernicus's model. He was able to observe the planets with the newly invented telescope.