Theorys about the universe.

 Claudius Ptolemy
(AD 100-165), a great Greek astronomer, argued that the stars and planets moved around the Earth in circles, because the circle was a perfect shape created by the gods. This is what scientist call the Geocentric theory. His description of how the universe worked was accepted for more than 1,500 years, when
Nicolas Copernicus (1473-1543) noticed that the movements of the Earth could be better explained if the Sun, not the Earth, lay at the centre. This is called the Heliocentric theory. Like Ptolemy, Copernicus believed that the planets moved in circles, but Johannes Kepler (1571-1630) showed that their orbits were elliptical (oval-shaped).