Astronomy# Claudius Ptolemy

## Who was Claudius Ptolemy?

## Biography of Claudius Ptolemy

## What Claudius Ptolemy discovered

## Ptolemy’s theory

## Ptolemy’s map

## Claudius Ptolemy’s contributions

**Claudius Ptolemy**, a scientist of Egyptian origin, was an important **astronomer**, **mathematician** and Greek **geographer** who flourished in **Alexandria** during the 2nd century A.D. His writings represent the culminating achievement of **Greco-Roman** science, mainly if we refer to his geocentric model, which was based on the center of the earth as a model of the universe, what we now know as **Ptolemaic** system. He was an **astrologer** who believed that astrology was a legitimate but **inaccurate** **science**. His approach to astrology was quite practical; he thought that astrology was useful but should not be trusted completely.

**Personal information**

**When was he born**: Year 85**Where was he born**: Alexandria, Egypt**When did he die**: Year 165**Where he died**: Alexandria, Egypt

Claudius Ptolemy was the **last great representative of Greek astronomy**, great observer, mathematician, geographer and scientist, whose main work influenced Arab and European astronomy until the Renaissance and creator of the geocentric model and Ptolemaic system.

Apparently, he was born in **Ptolemy**, around the year 85 and died in **Alexandria** in the year 165. Claudius Ptolemy grew up to become a **mathematician**, **astrologer**, **astronomer** and a recognized writer. His name, Claudius Ptolemaeus indicates that he lived in **Egypt** and “Claudius” means that he was a **Roman** citizen. In fact, ancient sources state that he lived and worked in Alexandria, Egypt. Ptolemy created several **scientific treatises**. His first and one of the most important work was the astronomical treatise known as the Almagest, which was initially called the “**Mathematical Treatise**“. This was an extensive text containing an outline of Aristotle’s **cosmology**, which included topics such as year duration, the Sun’s and Moon’s motion, the Moon’s motion, the fixed star movements and **planets**, among other areas of astronomical relevance.

Ptolemy made great **geographical** discoveries in which he created precise maps using different **projection** systems and discovered the **geographical coordinates** to locate places on earth. He discovered the theory of mirrors and light **reflection** and **refraction**. He explained the mathematical theory that gave **movement** to the moon, sun and planets.

Ptolemy’s theory is known as **Geocentric Theory**. In this theory, which is his most important creation and research, Claudius Ptolemy believed that the **earth** was in a **static** position and therefore occupied the **center of the Universe**, and that the Sun, Moon, stars and planets were revolving around it. He looked for a way to solve the two main questions regarding planetary motion, planet **retrogradation** and the **increase** they produce when they retrograde, and the different duration of sidereal revolutions. In his system, each of the planets moves through two or more spheres, one of them is centered in the earth and the other is the epicycles that fit in the deferent.

The name of this work was *“ Geography“* and in it, he gathered all the knowledge he had of Greek-Roman world. His

Claudius Ptolemy’s fundamental contribution was his **model of the Universe**. He applied astronomy to astrology and thus created **horoscopes**. Through his map, he contributed to the use of **longitude** and **latitude** lines and the specification of places on earth by observing the sphere. He taught us about the different properties of light, mainly **refraction** and **reflection** through his work called Optics, which was a treatise on mathematical theory regarding light properties. He was the first to conduct research on the **Law of Refraction**. He influenced the astronomical and mathematical thoughts of the 16th century through his **geocentric system**. He perfected the methods of map projection and introduced the terms we use today: **parallels** and **meridians** to establish lines of longitude and latitude.

Written by Gabriela Briceño V.

Briceño V., Gabriela. (2019). *Claudius Ptolemy*. Recovered on 1 October, 2023, de Euston96: https://www.euston96.com/en/claudius-ptolemy/