Ancient Science · Part 22 · Maps · B2
Ptolemy: The Almagest, the Geography and Astrology
Part 22 of Ancient Science: Claudius Ptolemy, the last great astronomer of Alexandria, built a model of the heavens that predicted the planets for fourteen centuries, mapped eight thousand places from Ireland to China, and wrote a book on astrology. Sophia shows what could be measured, what had to be guessed, and why later scholars began to doubt him. It can be calculated, it must be corrected, with Philo, Sophia, Marcos and Demetria.
Tonight, the last great astronomer of Alexandria, who will work in this city about a hundred and fifty years after you, Philo: Claudius Ptolemy.
He did, and his system was so good at predicting the planets that it was used for fourteen hundred years. He also made a map of the world with eight thousand places on it, and wrote a book on astrology.
Read: one man’s map of the heavens and the Earth
Claudius Ptolemy worked in Alexandria in the second century CE. His observations can be dated between 127 and 141 CE. Almost nothing else is known about his life.
His great work on astronomy, the Almagest, in thirteen books, explains the movements of the sun, the moon and the planets around a still Earth, using circles on circles called epicycles, off-centre circles, and a point called the equant. His methods could be used to calculate where any planet would be on any night, years in advance. The book also contains a catalogue of 1,022 stars.
His Geography lists about eight thousand places, from Ireland to China, each with a latitude and a longitude, and explains how to draw a map of the round Earth on a flat surface. His Tetrabiblos explains astrology: Ptolemy believed that the stars influence events on Earth, though not in every detail.
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