De revolutionibus orbium coelestium have begun work on his new system by that time. Most historians believe that he wrote the "Commentariolus" after his return from Italy, possibly only after 1510. At this time, Copernicus anticipated that he could reconcile the motion of the Earth with the perceived motions of the planets easily, with fewer motions than were necessary in the "Alfonsine Tables", the version of the Ptolemaic system current at the time. In particular, the heliocentric Copernican model made use of the Urdi Lemma developed in the 13th century by Mu'ayyad al-Din al-'Urdi, the first of the Maragha astronomers to develop a non-Ptolemaic
Science and technology of the Han dynasty Han astronomers believed the Sun, Moon, and planets were spherical like balls or crossbow bullets. He also wrote that the Moon and planets produce no light of their own, are viewable to people on Earth only because they are illuminated by the Sun, and those parts not illuminated by the Sun would be dark on the other side. For this, Jing compared the Moon to a mirror illuminating light. In the 2nd century CE, Zhang Heng drew a similar comparison to Jing's by stating that the Sun is like fire and the Moon and planets are like water, since fire