Database: Calculating the Earth's Circumference

In Abbasid Baghdad, every scholar knew that the Earth was spherical. They knew it because they had read about it in translated Ancient Greek manuscripts, most importantly Ptolemy's , which was translated by the great Abbasid astronomer al-Sufi. They also knew it because they had used simple geometric concepts and trigonometric equations to calculate its circumference.
Around 240 BCE, a Greek mathematician named Eratosthenes had used shadows projected by wooden rods to calculate that two cities were separated by 7 degrees, or 1/50th of a sphere. He then multiplied the distance between these two points by 50 to get the size of the Earth, within 5% of modern calculations. Sometime around 830, a team of 70 mathematicians, including the famous mathematician al-Khwarizmi (780-850) recreated his experiment. Improving on their predecessor's method, they tried to diminish the risk of error by using points separated by a single degree. Traveling from Baghdad to the surrounding desert and trying to follow a North-South road, they stopped when they reached a point where the elevation of the had changed by a degree. Their calculations were similar to those of Eratosthenes. Later, another scientist, al-Biruni (973-1050), got even better results by using a mountain as his measuring rod!
Both expeditions were motivated in part by the desire to know the extent of their territory compared to their rivals, and by Islam's to pray facing 's , no matter your position in the world. A proof that religious belief and scientific pursuits don't always come into conflict.
Category:Database: Art and Science