Ptolemy

Claudius Ptolemy was an Egyptian astronomer, mathematician, and geographer of Greek descent who flourished in Alexandria during the 2nd century CE. He is famously known for his geocentric model of the universe known as the Ptolemaic system. This astronomical system proposed by Ptolomy dominated science for almost 1500 years. Ptolomy’s astronomical works were enshrined in his great book “The mathematical syntaxis” which came to be known as the Almagest. This major astronomical work was completed about 150 CE and contains reports of astronomical observations that Ptolemy had made over the preceding quarter of a century. The book which is of encyclopediac nature became the most authoritative reference book in astronomy for centuries after centuries. Ptolomy believed that the motions of the heavenly bodies could be explained in mathematical terms. He argued that,Earth is a stationary sphere at the centre of a vastly larger celestial sphere that revolves at a perfectly uniform rate around Earth, carrying with it the stars, planets, Sun, and Moon—thereby causing their daily risings and settings. Through the course of a year the Sun slowly traces out a great circle, known as the ecliptic, against the rotation of the celestial sphere. The Moon and planets similarly travel backward against the “fixed stars” found in the ecliptic. Hence, the planets were also known as “wandering stars.” The fundamental assumption of the Almagest is that the apparently irregular movements of the heavenly bodies are in reality combinations of regular, uniform, circular motions. The geocentric system of Ptolomy was dogmatically asserted by western world until it was challenged by Coppernicus’ heliocentric system