   But observers realized that the heavenly bodies did not move as Aristotle postulated. The earth was not the true center of the orbits and the motion was not uniform. The most obvious problem was that the outer planets seemed to stop, move backwards in ‘retrograde’ motion for a while, and then continue forwards. By the second century, when Ptolemy compiled his Almagest (this common name of Ptolemy’s Syntaxis was derived from its Arabic title), astronomers had developed the concept that the orbit moves in ‘epicycles’ around a ‘deferrent,’ that is, they move like a flat heliacal coil around a circle around the earth. The earth was also off-center, on an ‘eccentric,’ as the heavenly bodies moved around a central point. Ptolemy added a point on a straight line opposite the eccentric, which is called the ‘equalizing point’ or the ‘equant,’ and around this point the heavenly bodies moved uniformly. Moreover, unlike the Aristotelian model, Ptolemy’s Almagest did not describe a unified universe. The ancient astronomers who followed Ptolemy, however, were not concerned if his system did not describe the ‘true’ motions of the heavenly bodies; their concern was to ‘save the phenomena,’ that is, give a close approximation of where the heavenly bodies would be at a given point in time. And in an age without professional astronomers, let alone the telescope, Ptolemy did a good job plotting the courses of the heavenly bodies.