For instance, while no one can doubt the genius of Copernicus and his heliocentric model of the solar system in heralding the age of modern astronomy, it is not commonly known that he relied on work carried out by Arab astronomers many centuries earlier. Many of his diagrams and calculations were taken from manuscripts of the 14th-century Syrian astronomer Ibn al-Shatir. Why is he never mentioned in our textbooks? Likewise, we are taught that English physician William Harvey was the first to correctly describe blood circulation in 1616. He was not. The first to give the correct description was the 13th-century Andalucian physician Ibn al-Nafees.