In the Planetary Hypotheses, Ptolemy summarizes the planetary models that he discusses in great detail in the Almagest, but he changes the mean motions to account for more prolonged comparison of observations. But it is wise not to forget that the existence of the Roman Empire was an essential condition for the transmission of Hellenistic science to the Muslim world. What Sā’id calls “the Romans” and “the Egyptians” in part coincides with what we would call the Byzantines and the Alexandrian School, while Rome and Egypt in our sense of these words could not compare in importance with India and the Hellenistic or Muslim contributions. 1068 Abū’l-Qāsim Sā’id ibn Ahmad, also known as Qādi Sā’id, wrote a book entitled The Categories of Nations.1 In this work he discusses the people of the world from the viewpoint of their interest in scientific research, stating that “the category of nations which have cultivated the sciences forms the élite and the essential part of the creations of Allah.”2 Eight nations belong to this class: “the Hindus, the Persians, the Chaldeans, the Hebrews, the Greeks, the Romans, the Egyptians, and the Arabs.”3 Taking into account some terminological differences, this list can still be considered fairly complete. The same method would work for the inner planets if conjunctions were observable, but theyĪre not, and the variation of the observable synodic events-first and last morning and evening visibilities-is dominated moreīy the motion of the planet in latitude than the nonuniform motion of the epicycle center. Have used those models to estimate approximate values for the eccentricity e and longitude of apogee A required for geometrical models. Greek astronomer with a reasonable understanding of Babylonian System A models for the outer planets and the Sun–Moon could Of mean oppositions by Babylonian models could serve as useful proxies for real empirical observations. A Greek astronomer might have realized that the predictions The longitude and time of oppositions of the planet with the mean Sun. One way to isolate the motion of the epicycle center is to determine The deferent from the motion of the planet on its epicycle. Geometrical models used by the Greeks, the practical difficulty is to somehow isolate the motion of the epicycle center on Models of planetary motion as observed from Earth must account for two principal anomalies: the nonuniform speed of the planetĪs it circles the zodiac, and the correlation of the planet’s position with the position of the Sun.
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