Definition

1. Proper noun:
   • Claudius Ptolemaeus, known in English as Ptolemy, was a Greco-Roman mathematician, astronomer, geographer, and astrologer who lived and worked in Alexandria, Egypt, during the 2nd century AD. He is most famous for proposing a comprehensive geocentric (Earth-centered) model of the universe, which was the dominant cosmological system in the Western and Islamic worlds for over a millennium.

Usage Examples

• Proper noun:
  • The astronomical theories of Claudius Ptolemaeus were not seriously challenged until the time of Copernicus.
  • In his work the Almagest, Claudius Ptolemaeus compiled the knowledge of ancient Greek and Babylonian astronomy.

Advanced Usage

• "The Ptolemaic system": This phrase refers specifically to the geocentric cosmological model developed by Claudius Ptolemaeus, which used complex systems of epicycles and deferents to explain the observed motions of the planets.
  • The Ptolemaic system was a remarkable achievement of mathematical astronomy, even though its core premise was incorrect.

Variants and Related Words

• Ptolemy (n): The common English name for Claudius Ptolemaeus.
  • Ptolemy's map of the world was influential for centuries.
• Ptolemaic (adj): Of or relating to Claudius Ptolemaeus or his theories.
  • The Ptolemaic model placed Earth at the center of the cosmos.

Synonyms

• Ptolemy: The direct and most frequently used synonym in English.

Noun

1. Alexandrian astronomer (of the 2nd century) who proposed a geocentric system of astronomy that was undisputed until the late Renaissance