Claudius Ptolemy
Ptolemy was the most influential Greek astronomers and geographers of his time, even though now most of his theories were later proved wrong or incorrect. He invented the geocentric theory that has been prevailed for 1400 years even though he lived from 87 to 150 CE it has been existed for that long. Ptolemy knew that Earth was a sphere and not a flat disk, which this was one of the facts that haven’t been accepted for many more centuries. He was also famous with giving many of the constellations the names and for creating complex star charts and world maps. About 2000 years ago he tried to explain the apparent motion of the Sun and the planets in the sky. When he was observing, he only used just a very simple tool called the astrolabe to chart the sky. Astrolabe is something like a protractor, it also measures angles. He has propounded geocentric, or Earth-centered, and model of universe. This model that he called the celestial sphere, in the centre there is the Earth with all the planets and stars at fixed positions within eight concentric spheres that spun in circles called orbits. Ptolemy first has mentioned that the Earth did not move and was located at the center of the universe. The Greek culture believed that the planets and stars moved continuously in perfect circular orbits. He also has proposed that the planets, Sun, and Moon moved in small circles while traveling in their larger orbits around the Earth. What he has actually described was a model of our solar system, not the universe. At this moment most of people didn’t understand about the existence of galaxies. Ptolemy’s model enabled astronomers to create the first Christian calendar by explaining a method for humans to navigate the globe. This description of the universe lasted more than 1000years until Nicolaus Copernicus rejected his idea and developed his own heliocentric system.