Christiaan Huygens was a Dutch mathematician, astronomer, and physicist. He was born on April 14, 1629 in The Hague, Netherlands, where he later died on July 8, 1695. He is best known as a founder of the wave theory of light, inventor of the pendulum clock, and for his discovery of the true shape of Saturn’s rings. Not very much is known about his personal life. Christiaan Huygens was the second of five children born to a wealthy and important family. His father, Constantijn Huygens, was a prominent poet, diplomat, and Latinist. His mother, Suzanna van Baerle, died soon after the birth of his sister in 1637. From a young age, he had the opportunity to interact with some of the prominent scientists of his time through his father, namely René Descartes. He was taught at home by private tutors, and his early efforts in geometry impressed Descartes, who would occasionally visit the household. In 1645, Huygens began studying math and law at the University of Leiden and two years later, he entered the College of Breda to study the same subjects. He was elected to the Royal Society, which was a newly formed group that aimed to improve scientific knowledge and is still in existence today, in 1663. In 1666, Huygens became a founding member of the French Academy of Sciences, which gave him a significantly larger pension than any other member and his own apartment in its building. He lived in Paris from 1666 to 1681 apart from his occasional visits to Holland. He respected the research of Sir Isaac Newton, who was also a member of the Academy, although he sometimes disagreed with it. He was sick throughout his entire life, although he was especially so during the final five years of his life. He never married or had children. From a young age, Christiaan was greatly influenced by René Descartes, with whom his father was a correspondent, and who was interested in and appreciative of his work. At the University of Leiden, Huygens studied math with the Dutch mathematician Frans van Schooten from May 1645-May 1647 until he left to go to the College of Breda, where he studied with John Pell, who was an English mathematician. Also during the time he was studying at the University of Leiden, his father brought his work to the attention of the French mathematician Marin Mersenne, which led to a direct correspondence between the him and Christiaan. Then, in 1660, he met Blaise Pascal, with whom he had already corresponded, while on a trip to Paris. Later on, he made the acquaintance of Gottfried Wilhelm Leibniz, who was a German mathematician and philosopher, and he remained on friendly terms with him for the rest of his life. In 1658, Christiaan Huygens made his first major contribution to science when he invented the pendulum clock. At the time, it was regarded as the most accurate way to measure time, and this did not change until quartz clocks were invented in the 1930’s. This pendulum clock was accurate to about 15 seconds a day, whereas the time keeping devices that were previously used were accurate to about 15 minutes a day. Huygens was inspired to create this clock by Galileo’s discovery of how isochronism related to the swing of a pendulum. It is also widely believed that Galileo had the original idea for a pendulum clock twenty years before Huygens was able to design a working model. Later on, in 1673, Huygens published his famous Horologium Oscillatorium, in which he wrote that the longer the swing of the pendulum is, the less accurate the clock will be. This led to clockmakers trying to create things to help regulate the clock’s designs, and, in 1690, the clocks were finally accurate enough that minute hands were regularly being added to clock faces. Huygens’ next major contribution to science was the discovery of Saturn’s rings in 1659. He was not the first to observe Saturn, however, as Galileo did so in 1610. But, due to the poor quality of Galileo’s telescope, he incorrectly guessed that the rings were two large moons. So, when he went to observe Saturn again two years later, he grew very confused because the “moons” had disappeared. Then, after another two years, he went to observe Saturn again and the “moons” had reappeared, so Galileo came to the conclusion that the rings were some kind of “arms”. But, due to improvements in the quality of telescopes, when Huygens went to observe Saturn, he was able to determine that the supposed “arms” were actually a system of rings. He also discovered one of Saturn’s moons, Titan, and the probe exploring Titan is now named after him because of this. Christiaan Huygens made his next great contribution to science in 1678 when he developed his wave theory of light. At the time, it was accepted that Newton’s theory that light was made up of particles was true. However, Huygens’ theory stated that light was made up of waves that vibrate up and down and perpendicular to the direction the light is traveling in. His theory, which is also known as Huygens’ Principle, proved to be the true theory of the motion of light waves in three dimensions. in. His theory also suggested that light waves peak from surfaces like “the layers of an onion”. In a uniform environment, such as a vacuum, the waves are spherical and the spread out as they travel at light speed. This explains why light shining through a small slit or hole spreads out instead of just going in a straight line.