Ptolemy, one of Alexander the Great's generals, was appointed satrap of Egypt after Alexander's death in 323 BC. In 305 BC he declared himself King Ptolemy I, later known as "Soter" (saviour). The Egyptians soon accepted the Ptolemies as the successors to the pharaohs of independent Egypt. Ptolemy's family ruled Egypt until the Roman conquest of 30 BC.
The dynastic history of Ptolemaic Egypt is very confusing, because all the male rulers of the dynasty took the name Ptolemy, and because many of them married their sisters, who were often called Cleopatra. The most famous member of the line was the last Ptolemaic queen, Cleopatra VII.
The dates in brackets are regnal dates for the kings. They frequently ruled jointly with their wives, who were often also their sisters. Several queens exercised regal authority, but the most famous and successful was Cleopatra VII (51 BC-30 BC), with her two brothers and her son as successive nominal co-rulers.
The system of Ptolemy, called the Ptolemaic universe, prevailed in astronomy for nearly fifteen hundred years, until the modern model of the solar system, with the sun at the center and the planets in motion, was developed from the ideas of Copernicus.
Ptolemy was the author of several scientific treatises, three of which would be of continuing importance to later Islamic and European science.
Ptolemy was concerned to defend astrology by defining its limits, compiling astronomical data that he believed was reliable and dismissing practices (such as considering the numerological significance of names) that he believed to be without sound basis.
Ptolemy's is a geocentric system, though the earth is the actual center only of the sphere of the fixed stars and of the "crank mechanism" of the moon; the orbits of all the other planets are slightly eccentric.
Ptolemy thus hypothesizes a mathematical system which cannot be made to agree with the rules of Aristotelian physics, which require that the center of the earth be the center of all celestial circular motions.
Ptolemy was the author of several scientific treatises, three of which have been of continuing importance to later Islamic and European science.
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