Ptolemy (87 - 150 AD). A Greek living in Alexandria, Ptolemy extended Hipparchus' theory of the solar system. Ptolemy's system involved at least 80 epicycles to explain the motions of the Sun, the Moon, and the five planets known in his time. He believed the planets and sun to orbit the Earth in the order: Mercury, Venus, Sun, MArs Jupiter, and Saturn. This system became known as the Ptolemaic system. Ptolemy was also a cartographer and geographer, and his maps remained the principal work on the subject until the time of Columbus.