English
عربى
中文
Deutsch
Español
Français
हिन्दी
Hrvatski
Italiano
日本語
Português
Română
Русский
Svenska
Türkçe
Tiếng ViệtCircles and PiEarth Arc
Arcs and Sectors
Most scientists in ancient Greece agreed that the Earth is a sphere. There was plenty of evidence: from ships disappearing behind the horizon at sea, to the circular motion of stars during the night.
Unfortunately, no one knew exactly how big Earth was – until around 200 BC, when the mathematician Eratosthenes of Cyrene (c. 276 – 195 BCE) was a Greek mathematician, geographer, astronomer, historian, and poet. He spent much of his life in Egypt, as head of the library of Alexandria. Among many other achievements, Eratosthenes calculated the circumference of the Earth, measured the tilt of the Earth’s axis of rotation, estimated the distance to the sun, and created some of the first maps of the world. He also invented the “Sieve of Eratosthenes”, an efficient way to calculate prime numbers.