March 14, 2021

Lyon astronomical clock, Lyon, France

Perfect timing

If the first day of daylight saving time doesn't have you springing for joy, this towering timekeeper might be more your speed. The astronomical clock at Lyon Cathedral in France was built in 1660, long before daylight time became widely adopted in the 20th century. The clock's intersecting hands and dials don't just tell time, they form a flattened model of our planet that tracks the positions of the sun and moon relative to Earth. The zodiac dial, offset to account for the planet's rotational tilt, shows the star sign currently in season.

All this movement of circles and spheres might call to mind another observance of the day: March 14 is Pi Day, in celebration of the mathematical constant pi (aka π, or roughly 3.14). You remember pi from geometry class: It expresses the ratio of the distance around a circle to the distance across it. So it was essential to ancient astronomers who mapped these celestial workings, as well as to designers of intricate machines that simulate the circling heavens.