The system of explaining planetary motion through concentric circles around the Earth improved through Ptolemy. His system involved more circles around planets orbiting Earth, with Earth being slightly off center in its own circle. The system was complex and incorrectly hypothesized that the Earth was at the center of the universe. Yet, Ptolemy was able to predict the place of the moon within one-sixth degree of arc in the sky. However, this theory might have set man back a few centuries rather than have advanced him. But at the time, it was the best model of the universe.