Claudius Ptolemy

There are few reliable sources of information on Claudius Ptolemy’s personal life. What is known for sure is that he lived and worked in Alexandria and died around 170 AD.

The crater Ptolemaeus on Mars is named after him, as is the asteroid 4001 Ptolemaeus. The Ptolemy Stone used in the mathematics courses at both St. John's College campuses is also named in his honor.

Not much is known about the circumstances of Claudius Ptolemy’s birth or his family. It is generally believed that he was born around 100 AD in Egypt, Roman Empire. He was of Greek descent, as deduced by his Latin name, Claudius Ptolemaeus.

The 14th century astronomer Theodore Meliteniotes gave Ptolemy’s birthplace as Ptolemais Hermiou in the Thebaid in an uncorroborated statement. However, the general consensus is that he was born in Alexandria where he is believed to have lived and died.

Claudius Ptolemy grew up to be a brilliant mathematician, astrologer, astronomer, and writer. Ptolemy was the author of several scientific treatises, and the order of their composition has been deduced from the dates mentioned in his surviving works.

His earliest major work was the astronomical treatise now known as the ‘Almagest’, although it was originally titled the ‘Mathematical Treatise.’ It was completed around 150 AD. The seminal work consisted of 13 sections, each of which covered an important subject.

The ‘Almagest’ was an extensive text which contained an outline of Aristotle's cosmology, the length of the year, the motion of the Sun, the motion of the Moon, lunar parallax, the motion of the lunar apogee, the motions of the fixed stars and planets, among other areas of astronomical relevance.

For drawing his models, Ptolemy adopted Hipparchus' solar model, which consisted of a simple eccentric deferent. He had inherited from his Greek predecessors a geometrical toolbox and a partial set of models for predicting where the planets would appear in the sky.

It is not known for sure how much of the ‘Almagest’ is original. Even though it was a major scientific text, some scholars over the past few centuries have cast doubts regarding its authenticity and have questioned Ptolemy’s credibility as an observer of heavenly bodies.

Ptolemy’s ‘Almagest’ is one of the greatest scientific texts of all time. It is a critical source of information on ancient Greek astronomy and its geocentric model was accepted for more than 1200 years from its origin. It was translated into several languages over the centuries.

His work ‘Geographia’ was a seminal treatise on cartography in which he provided latitude and longitude co-ordinates for numerous places and geographical features in the world. He also improved the methods of creating maps.

He authored ‘Tetrabiblos’, a text on the philosophy and practice of astrology in which he gave the study of the effects of astronomical cycles on earthly matters. Over the preceding centuries, this influential text was copied, abridged, and translated into many languages.