The Greek scientist Ptolemy was born almost two thousand years ago. He lived and worked in Alexandria, Egypt. In those days, Egypt was part of the Roman Empire. From watching how the other planets moved, Ptolemy thought that the Earth was the center of the universe. He thought that the other planets and the sun rotated around Earth. This came to be known as the Geocentric Model of the universe. Ptolemy’s Geocentric or earth-centered model was wrong, but people kept on believing this idea for another 1,400 years.