We began dividing up time into shorter units—seconds, minutes, hours—with many of those units relying on a base-12 counting system passed down from the ancient Egyptians and Sumerians. Time was defined by grade-school division: a minute was one-sixtieth of an hour, an hour was one-twenty-fourth of a day. And a day was simply the time that passed between the two moments when the sun was highest in the sky.
