# Who is Claudios Ptolemy?

June 25, 2021Ptolemy was a Greek astronomer, mathematician, geographer and astronomer from Alexandria. Approximately MS. He is considered to have lived between 85 and 165 years.

Ptolemy

Ptolemy is one of the famous scientists who lived in the Late Alexandrian Period (first half of the 2nd century AD). There is almost no information about the Life of Ptolemy. Muslim astronomers say that he lived to be 78 years old. It is claimed that Ptolemy was an Egyptian of Greek origin, or a Greek of Egyptian origin.

Ptolemy is the author of two important works: “The Great Composition” and “Geography”. These works have an important place at the end of the Middle Ages in Europe. The translation of the books into Latin was made only in the 12th century.

The “Great Composition” (Arabic: Kitab el Macisti, Latin: Almagest, Greek: Mathematike Syntatksis) is a collection of astronomical knowledge from the Greek and Babylonian civilizations. Most of the compilation is based on Hiparkus, who lived three centuries before him. An Earth-centered Solar System model is suggested in the work. This model has been accepted as the valid model in the Western and Islamic worlds until Copernicus’ heliocentric model. The book also includes a review of plane and spherical trigonometry.

Ptolemy

Another important work of Ptolemy, “Geography” is also a compilation. Geography information known in the Roman Empire of the age is collected in this book.

Ptolemy made contributions to the fields of astronomy, mathematics, geography and optics; but he is best known for his work in astronomy. He synthesized the astronomy knowledge that had survived to his time and collected them in his work titled “Mathematice Syntaxis”. This work was later called “Megale Syntaxis” (Great Collection), and when it was translated into Arabic, its name was changed to al-mecistî because the Arabic letter-i descriptor was added to its head; It is now known in the Western world as the Almagest, since it was later translated from Arabic into Latin as the Almagest.

The Almagest consists of thirteen books:

Book One outlines the geocentric system with its proofs;

Book Two contains information on spherical trigonometry and a table of chords, with Menelaus’ theorem; example problems are also solved here;

The Third Book describes the movement of the Sun and the annual period;

The Fourth Book deals with the movement of the Moon and the monthly period;

Book Five deals with the same issues. It discusses the distances of the Moon and the Sun, as well as provides detailed information on the construction and use of an astrolabe;

Book Six examines the conjunctions and encounters of the planets, eclipses of the Sun and the Moon;

Books Seven and Eight are about still stars; includes the famous discussion of motion, Ptolemy’s catalog of stationary stars, and the necessary method for making a celestial globe instrument;

The remaining five books are devoted to the movements of the moving stars, namely the planets, and are the most original part of the work.

In this work, Ptolemy introduces the geometric theory that he established to make sense of the celestial phenomena with its main lines; In this theory, which is based on Aristotelian physics, the universe is spherical and the Earth stands motionless at the center of this universe. If the daily or annual manifestations were the result of the movements of the Earth, everything would spill into space and the Earth would be torn apart.

The Moon, Mercury, Venus, Sun, Mars, Jupiter, Saturn and the fixed stars make circular motions around the Earth at regular speeds. The sphere of fixed stars is the end of the universe.

However, given that the Earth is at the center and the celestial bodies regularly revolve around it, some of his observations, such as the Moon and Sun approaching and departing from the Earth, sometimes gave the quickest and most comprehensive information; because the calculations of classical astronomy, which are within the limits of spherical astronomy, are based on spherical geometry.

Ptolemy’s World Map

Hipparchus (150 BC), who lived about three centuries before Ptolemy, declared that angles could be measured with beams and prepared a ruler for beams; however, since his work on the subject has been lost, it is not known how he arranged this ruler. The beams of some bows were very easy to find and these beams were called main beams; but other than these, finding the beams of the bows required lengthy operations. Therefore, while Ptolemy was preparing the ruler of chords, by using the Ptolemy Theorem (AB . CD + AD . BC = AC . BD) regarding quadrilaterals drawn in a circle, chords of the sum and difference of angles (beam (AB), chord (A+B), beam A/2 , beam 2A) had gone the way of finding.

Ptolemy, who was also one of the leading optics researchers of his time, adopted the view that vision occurs through visual rays emanating from the eye, like most of the previous opticians. However, he also gave a physical interpretation of the visual dispersion and stated that this dispersion was not in the form of a discontinuous and intermittent cone, but in the form of a continuous and continuous pyramid. If it were not so, that is, the rays