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Eratosthenes ( 276 BC - 194 BC) was a Greek mathematician, geographer and astronomer with (probably) Chaldean origins.
He was born in Cyrene (now Shahhat , Libya) and he died in Ptolemaic Alexandria. He is noted for devising a system of latitude and longitude and computing the size of Earth.
Eratosthenes studied at Alexandria and some years in AthensAcropolis in central Athens is home to ancient monuments of Athens — a mainstay of its thriving tourism industry Athens ( Greek: Athina is the capital of Greece, and also the capital of the Attica region of Greece. A cosmopolitan modern city, Athens is al. In 236 BCCenturies: 4th century BC 3rd century BC 2nd century BC Decades: 280s BC 270s BC 260s BC 250s BC 240s BC 230s BC 220s BC 210s BC 200s BC 190s BC 180s BC Years: 241 BC 240 BC 239 BC 238 BC 237 BC 236 BC 235 BC 234 BC 233 BC 232 BC 231 BC Events Eratosthene he was appointed by Ptolemy III Euergetes IPtolemy III Euergetes I Ptolemaeus III Evergetes Euergetes ( 246 BC- 222 BC). The third ruler of the Ptolemaic dynasty of Egypt, he was the eldest son of Ptolemy II of Egypt Philadelphus and Arsinoe II of Egypt. He came to power in 246 BC upon the death o as a head and the third librarian of the Alexandrian library. He made several important contributions to mathematicsMathematics is commonly defined as the study of patterns of structure, change, and space; more informally, one might say it is the study of "figures and numbers". In the formalist view, it is the investigation of axiomatically defined abstract structures and scienceFor the scientific journal named Science see Science (journal). Science is both a process of gaining knowledge, and the organized body of knowledge gained by this process. The scientific process is the systematic acquisition of new knowledge about a syste. He was a good friend to ArchimedesSee also Archimedes computer, Archimedes (disambiguation). Archimedes of Syracuse (circa 287 BC 212 BC), was a Greek mathematician, astronomer, philosopher, physicist and engineer. He was killed by a Roman soldier during the sack of the city, despite orde. Circa 255 BCCenturies: 4th century BC 3rd century BC 2nd century BC Decades: 300s BC 290s BC 280s BC 270s BC 260s BC 250s BC 240s BC 230s BC 220s BC 210s BC 200s BC Years: 260 BC 259 BC 258 BC 257 BC 256 BC 255 BC 254 BC 253 BC 252 BC 251 BC 250 BC Events First Punic he invented the armillary sphereAn armillary sphere (also known as spherical astrolabe is a model of the celestial sphere, invented by Eratosthenes in 255 BC. Its name comes from the latin armilla (circle, bracelet), since it has a skeleton made of graduated metal circles linking the po, which was used till 17th century.
He calculated the earth's circumference circa 240 BC, using trigonometry and information on the altitude of the Sun at noon in Alexandria and Syene (now Aswan, Egypt). The calculation is based on the assumption that the Sun is so far away that its rays can be taken as parallel.
Eratosthenes knew that on the summer solstice at local noon on the Tropic of Cancer, the Sun would appear at the zenith; Aswan is in fact slightly north of the tropic. He also measured that in his hometown of Alexandria, the position of the Sun would be 7° south of the zenith at that time. He knew that this angle was 7/360 of a full circle. Asumming that Alexandria was due north of Syene - Alexandria is in fact on a more westerly longitude - he concluded that the distance from Alexandria to Syene must be 7/360 of the total circumference of Earth. The actual distance between the cities was known from caravan travellings to be about 5,000 stadia. He established a final value of 700 stadia per degree, which implies a circumference of 252,000 stadia. The exact size of the stadion he used is no longer known (the common Attic stadion was about 185 m), but it is generally believed that Eratosthenes' value corresponds to between 39,690 km and 46,620 km. The actual circumference of the Earth around the poles is 40,008 km. Eratosthenes' method was used by Posidonius about 150 years later.
Circa 200 BC Eratosthenes adopted a word geography, which means a description of the Earth.
Eratosthenes' other contributions include:
Eratosthenes was known under the name β, because he proved himself to be the second in the world in many fields and he was also supposedly known for his haughty character. In 195 BC he became blind and a year later he starved himself to death.