Ptolemy

what did ptolemy believe was the centre of the universe

earth

what did he produce to track the position of the sun, stars and planets

tables

what sort of model was it

hypothetical model

what did it lack

observed evidence

how did ptolemy believe planets moved

perfect circles around earth, epicycle

what assumption did he have to make to make his theory work

assume that epicycles did not move around the earth but around another point far from earth, halfway between the earth and another point called the equant

why were equants important

it meant that he could account for the apparent changes in speed as the planets were in orbit but also maintain a system of perfect cycles

why was it important that all spheres and orbits were perfect

it became too complex if they changed