In the early 11th century the great Islamic scientist al-Biruni (born 973, died 1048 - full name Abu Arrayhan Muhammad ibn Ahmad al-Biruni) devised a method to efficiently measure the radius of the earth. A little more than a thousand years earlier, the Greek mathematician Eratosthenes (276-194 BC) had computed the circumference of the earth but his method required measuring a distance between two cities far apart from...