Dutch astronomer, physicist, and mathematician Christiaan Huygens (1629–1695) is one of the most important figures in the history of science. He was a key transitional scientist between Galileo and Newton. His work was crucial to the development of the modern sciences of mechanics, physics, and astronomy. Huygens helped develop the Law of Conservation of Momentum, invented the pendulum clock, and was the first person to describe a wave theory of light. He designed and built the clearest lenses and most powerful telescopes of his time. Using these tools, he was the first person to identify Saturn’s ring system, and he discovered Saturn’s largest moon, Titan.