Claudius Ptolemy
A Greco-Roman mathematician, astronomer and astrologer of the second century, working in Alexandria. His Almagest set out the geometry of the heavens that Europe and the Islamic world used for over a thousand years, and his Tetrabiblos became a foundational text of Western astrology.
The Almagest
Ptolemy’s great astronomical work laid out a geocentric model of the cosmos and a catalogue of the stars in such complete form that it remained the standard reference until Copernicus, more than 1,300 years later.
The Tetrabiblos
Its title means "four books". In it Ptolemy set astrology on the same rational footing he gave astronomy, and the work became the classic statement of the tradition’s theory in the West.
His legacy
The projection behind the astrolabe traces to Ptolemy, and the "Ptolemaic system" named after him described the sky for the entire medieval world.
Connections
- The Astrolabe — An ancient instrument for measuring the altitude of stars and planets and for solving problems of time and position in the sky. Often called the first analogue computer, it let a single hand-held disc tell the time, find a body’s place and model the turning heavens.
- William Lilly — A seventeenth-century English astrologer, the most famous of his age. His Christian Astrology (1647) was the first major textbook of astrology written in English rather than Latin, and his name is bound up with horary astrology — answering a question from the chart of the moment it is asked.