Explain the differences between the geocentric theory and the heliocentric theory of the universe.
The Geocentric and the Heliocentric models are descriptions of the universe known at the time when these models were developed. The main difference between the two models is the perceived center of the known universe. According to the geocentric model, Earth is the center of the known universe or the solar system. This model states that the Sun and all the planets orbit the Earth. In comparison, the heliocentric model states that the Sun is the center of solar system and that all the planets orbit around it. The geocentric model is also known as the Ptolemaic model of the universe, since Ptolemy was a big supporter of this model and also refined it to explain the observations of celestial bodies. However, the geocentric model failed to explain the retrograde motion of Mars (it seems to go backwards and then forwards). The heliocentric model was developed much later in the sixteenth century by Copernicus and explained the observations of celestial bodies much better.
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