Lyon astronomical clock, Lyon, France

© kyolshin/Alam

Perfect timing!

Today is the first day of daylight saving time in the US that means the clocks move forward by one hour, with the time changes taking place at 2:00 am local time. Here you are seeing the astronomical clock at Lyon Cathedral in France that 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.