His work in astronomy required accurate timekeeping, and clocks available at the time “were regulated by slowly falling weights, which would turn the devices’ gears. Unfortunately, the pace of the weight’s descent was irregular, and the clocks were wildly inaccurate.” Huygens studied the relation of the length of a pendulum to its period of oscillation and developed a system that combined the pendulum with a weight-driven clock.
He developed a prototype for the clock by the end of 1656 and patented the design on June 16 of the following year. The concept behind the invention of the pendulum clock has been credited to Galileo. His son, Vincenzo, sketched a clock based on his father’s theories (see image below), but the clock was never built.
Huygens solved the essential problem in Galileo's concept by "making the period of a pendulum truly constant by devising a pivot that caused the suspended body, or bob, to swing along the arc of a cycloid rather than that of a circle." His design made clocks more reliable and accurate to better than one minute per day.
Huygens contracted his clock design (see image at right) to Dutch clockmaker Salomon Coster, who in 1657 actually built the clock. It is on display at the Boerhaave Museum in Leiden, the Netherlands.
Huygens later invented the spring-powered clock that eventually allowed for the determination of longitude at sea.
Using lenses he ground himself, Huygens also made several landmark astronomical discoveries, including the shapes of the rings of Saturn, as well as that planet’s largest moon, later named Titan. He also observed Mars and drew its first map.
Among his other contributions to science, he was credited with founding the wave theory of light and is regarded as one of the founders of the science of dynamics—the study of the action of forces on bodies.
On January 14, 2005, a NASA space probe, named after Huygens and part of a European Space Agency (ESA) mission that launched from Earth on October 15, 1997, landed on Titan, the moon he'd discovered.
In a 1687 letter to fellow mathematician Ehrenfried Walter von Tschirnhaus, Huygens wrote of his approach to research: “ ... great difficulties are felt at first and these cannot be overcome except by starting from experiments ... and then be conceiving certain hypotheses ... But even so, very much hard work remains to be done and one needs not only great perspicacity but often a degree of good fortune.”