**(April 14, 1629 – July 8, 1695)**

An outstanding 17th century researcher, Christiaan Huygens explored mathematics, physics, and philosophy. He corresponded with Pierre de Fermat, Blaise Pascal, and René Descartes. He also taught a young Gottfried Leibniz maths. After studying Galileo’s works, Huygens built the first pendulum clock. The accuracy of this invention ensured that it remained in vogue for nearly 3 centuries. (From the 1650s until the 1930s when quartz took over, pendulum clocks were the most accurate man-made timepieces). He is also credited with developing balance-spring-watch independently of Robert Hooke. Regarding optics, Huygens presented his Wave Theory of Light to an erudite forum at the Paris Science Academy, who appreciated it. His skills as a lens-maker enabled him to exchange ideas with Baruch Spinoza and Antonie van Leeuwenhoek. With the telescopes he built, he was able to study Mars’ peripheries: before focusing on Saturn, its rings and its largest moon (Titan). His contributions to mathematics were mostly in Geometry, Algebra, Statistics, and Applied Maths. These include research on the motions of objects, their impacts upon collisions, as well as gravity. In the process, he became the first European known to have formulated mathematical equations while expressing physics laws. Christiaan Huygens was not an avid publisher of works; yet, he published the first European book on Probability Theory: after learning the theme from Fermat and Pascal. His other treatises pertained mostly to astronomy and optics. Among his eponyms are: the* Huygens-Fresnel* principle, the *2801 Huygens* asteroid, and the 467-kilometer-wide *Huygens* crater located inside Mars’ lapygia quadrangle.

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