Posidonius

Posidonius (135 BC - 51 BC), was a Greek philosopher, astronomer, geographer and meteorologist.

Nicknamed "the Athlete", he was born in Apamea, northern Syria, and probably died in Rome.

Posidonius was a student of Panaetius of Rhodes. He was a stoic with many influential friends. His pupils were Cicero and Pompey. Some of his researches were valuable. As Pytheas he believed the tide is caused by the Moon. He travelled to the west to the Atlantic ocean. In about 90 BC he estimated the astronomical unit to be a₀/r_E = 9893, what was still for a 1/2 too small. He measured the size of the Sun, which was greater and more accurate than one proposed by other Greek astronomers and Aristarchus. He used Eratosthenes' method and measured Earth's circumference from the position of the star Canopus. His value was 240,000 stadia.

He wanted to master the whole knowledge of that time, similar as Aristotle or Eratosthenes did.

External links:

• Theosophy Library Online page: http://theosophy.org/tlodocs/teachers/PosidoniusOfApamea.htm
• Technology Museum of Thessaloniki page http://www.tmth.edu.gr/en/aet/7/82.html