Tetrabiblos was created in 1##.

Some of the books he wrote include:

1. The Almagest (13 books long; It was originally titled the Syntaxis Mathmatica, which was called the Megale Syntaxis. When it was translated into Arabic it was called the al-Magisti, and when it was translated into Latin it was called the Almagestum. Finally it was translated into english-- The Almagest).

2. Tetrabiblos (Astrology/geography)

3. The Geographica (maps, atlas-- 7 books long)

4. A book on Optics which was reportedly 5 books long.

Claudius Ptolemy developed the mathematical astronomy used in Christian and Muslim countries up until the 16Thcentury.

Christopher Columbus and Magellan used Ptolemy's version of the world map during their voyage, but they did not know it was incorrect, thus not ending up where they planned to be.

He found the position of over one thousand stars.

Medieval people took their views on astronomy mostly from two great books, the Almagest and the Tetrabiblos, both by Claudius Ptolemaeus, or Ptolemy. He said there were two parts of astronomy, the easy and accurate part, and the hard part. The easy and accurate part was about predicting dates of the equinoxes, positions of the planets, phases of the moon, and so on, by mathematical calculations. The hard part was what we would call astrology, which was used to predict things about people's lives.

Ptolemy developed several mathematical models to describe the motions of the sun, the moon, the planets and the stars. The book that describes these models is called "The Almagest" or "Ptolemy's Almagest". The models all assume:

1. The earth is stationary.

2. All objects travel with uniform speed on a perfectly circular orbit.

However, a model that placed the earth in the centre of the orbits of all other objects would not work because it does not account for various anomalies, including the varying length of seasons, the irregularity of eclipses of the moons and the retrograde motion of the planets. Ptolemy used two mathematical devices to deal with the anomalies: eccentricity (an offset from the centre of a circle) and epicycles - circular orbits whose centre (or eccentric) itself traveled in a uniform circular orbit.

Much of the material in The Almagest was already known to Greek astronomers. Ptolemy's contribution was to consolidate all known results, make large improvements to the models, and to write it all down in a way that became a standard for the way to present the results of scientific enquiry.

His book was the standard text book for astronomers until his models were ultimately improved by Copernicus, Kepler and Newton.

Ptolemy also wrote a treatise on Astrology, based on his deep knowledge of the motions of the heavenly bodies. This work is called The Tetrabiblos.