Ptolemy His real name is Claudius Ptolemaeus, but we know him as Ptolemy. Not much is known about his life. The name Claudius probably means he was a Roman citizen. The name Ptolemy means that he was Greek. It is believed that he lived from 90 to 170 CE. They know that he worked in the library of Alexandria, Egypt from 127 to 150 CE. He was an astronomer, mathematician and geographer.

Discoveries He is famous for his work on astronomy and geography. His books were discovered in the Middle Ages, before the 12 th century. They were  Almagest – the study of astronomy and geometry  Tetrabiblios – the study of astrology  Geography – which included maps of how they thought the world was like at the time

Astronomy Ptolemy believed in the Greek geocentric view of the universe, that the Earth was at the center of the universe. He believed the planets and sun moved around the Earth in this order: Mercury, Venus, Sun, Mars, Jupiter, Saturn. This system is called the Ptolemaic system. It’s described in his book Almagest on astronomy. The book has information on the earth, sun, moon, stars and eclipses. It has a star catalog of 48 constellations that we still use today.

Mathematics He was also a mathematician. He discovered that any quadrilateral inside a circle with points A B C and D followed this equation, called Ptolemy’s theorem: AC*BD = AB*CD + DA*BC

Geography Claudius Ptolemy was very important in the history of geography and making maps. His book Geography was the main one used until Christopher Columbus. It had 8 volumes. The ancient Greeks and Romans knew that the earth was round. In his 1 st volume, he shows how to draw a spherical earth on a flat sheet of paper. He’s the first known person to do this.

Geography He was the first person to put a grid system on the map and he was the one who invented latitude and longitude. He was also the first to put north at the top of the map. The problem was that his map had many errors because he had to go by the estimates of merchant travelers who didn’t know how to measure longitude at the time.

Geography Ptolemy made the mistake of assuming that the earth had a shorter circumference. Because of this, Christopher Columbus thought he could reach Asia by sailing west from Europe. He landed instead in the NewWorld. Ptolemy made many contributions to geography. Even the mistake he made led Columbus to discover America in 1492.

Astrology Ptolemy was also an astrologer. His book Tetrabiblios was the most popular book on astrology at the time. He believed that the positions of the planets at the time of birth did influence a person, but not completely.

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