Ptolemy

1. Ptolemaic dynasty of Macedonian Greeks who ruled Egypt as pharaohs from 323 B.C., when Ptolemy, one of Alexander the Great's generals, took over Egyptian rule. The dynasty lasted until the death of the most famous member of the family, Cleopatra VII, in 31 B.C., shortly after the Battle of Actium. Egypt was then annexed to Rome.

2. Claudius Ptolemaeus (A.D. circa 85 - circa 165), known in the English language as Ptolemy, was a Greek astronomer who lived in Alexandria in Egypt.

Ptolemy was the author of the astronomical treatise which is now known as the Almagest (although that was not its original name). In this work he formulated a geocentric model of the solar system which remained the generally accepted model in the Western and Arab worlds for more than 1300 years. The Almagest also contains a star catalogue. Its list of 48 constellations is ancestral to the modern system of constellations, but unlike the modern system there were gaps between them.

Ptolemy also wrote several other books. In his Geography he attempted to map the known world and describe its peoples, although the results are often very inaccurate due to the absence of reliable data and his willingness to identify ethnic groups based on hearsay and folklore. In his Optics, a work which survives only in a poor Arabic translation, he writes about properties of light, including reflection, refraction and colour. His other works include Planetary Hypothesis, Planisphaerium and Analemma.