How did Eratosthenes calculate the circumference of the Earth?
Eratosthenes measured the angle of a shadow cast by a gnomon in Alexandria at noon on the summer solstice, finding it to be about 7.2 degrees, which is one-fiftieth of a full circle. He knew that at the same moment in Syene, rods cast no shadows at all. The distance between the two cities had been measured at about 5,000 stadia, so he multiplied by 50 to get roughly 250,000 stadia for the full circumference. Matthew's analysis of the result places it at approximately 40,338 km, compared to the modern equatorial measurement of 40,075 km.
Why was Eratosthenes called Beta or Second?
According to the Suda, a tenth-century reference work, critics gave Eratosthenes the nickname Beta (meaning Second, or Number 2) because he was not regarded as the leading expert in any single field. Strabo similarly described him as a mathematician among geographers and a geographer among mathematicians. His admirers countered with the nickname Pentathlos, after the Olympians celebrated for competing across many events.
When was Eratosthenes born and where was he from?
Eratosthenes was born in 276 BC in Cyrene, a Greek-founded city that is now part of modern-day Libya. He died around 196 BC in Alexandria at the age of eighty.
What is the Sieve of Eratosthenes?
The Sieve of Eratosthenes is an algorithm for finding all prime numbers up to a given limit by iteratively marking multiples of each prime as composite, starting with the multiples of 2. Hans-Joachim Waschkies has argued that Eratosthenes did not invent the underlying method, which was already known in antiquity, but that he coined the name "sieve" for it.
What was Eratosthenes' role at the Library of Alexandria?
Eratosthenes served as the chief librarian of the Library of Alexandria, summoned from Athens in 246 BCE after the incumbent librarian Apollonius of Rhodes was forced into retirement by Ptolemy III. The position also carried the role of royal tutor to the king's heir, making it the most prestigious academic appointment in the Greek world.
What did Eratosthenes contribute to geography?
Eratosthenes coined the words geography and geographer, wrote a three-volume work called the Geographika that recorded over 400 cities and their locations, divided the Earth into five climate zones, and overlaid the world map with a grid of parallels and meridians. He is named the Father of Modern Geography for this work. Julius Caesar later cited the Geographika in De Bello Gallico.