At Syene (now Aswan), located 800 km southeast of Alexandria in Egypt, the Sun's rays fall vertically at noon at the summer solstice. Eratosthenes, who was a Greek mathematician, geographer and astronomer (born in 276 BC) noted that at Alexandria, at the same date and time, sunlight fell at an angle of about 7° from the vertical. He assumed the Sun's distance to be very great. Given the distance between the two cities, he was able to calculate: