Christiaan Huygens (listen (help·info)) (April 14, 1629–July 8, 1695) was a Dutch physicist, mathematician and astronomer, born in The Hague. He was known for his idea that light was in the form of waves. He discovered Saturn's largest moon Titan in 1655. He also did detailed studies on Saturn's rings, and in 1656, he discovered that they are made up of rocks. He also studies optics and pendulum clock.