Eratosthenes

Eratosthenes was a Greek scientist who lived from 276 to 194 B.C. and studied astronomy, geography and math. He is famous for making the first good measurement of the size of the Earth. He was born in Cyrene which is in the modern-day country of Libya.  Eratosthenes is most famous for making the first accurate and good measurement of the size of Earth sometime around 240 B.C. He was also aware that there was no shadow at the bottom of a well in the town of Syene on the summer solstice which meant that the Sun must be straight overhead of Syene on that day. He measured the length of the shadow of a tall tower in Alexandria on the same day. He was hugely important and also gave us a formula for calculating prime numbers, he invented latitude and longitude, and calculated the circumference of the Earth and the distance of the Sun from the Earth. He was only approx. 1% off. He has also been known for creating a map of the earth based on the knowledge available at the time. He was very highly respected, and his calculations of the earth's circumference were used for hundreds of years. Today, his method for finding prime numbers from 1-100 is known as the 'Sieve of Eratosthenes' and is taught in math textbooks.