Just what is a second, exactly? The question has been open to interpretation ever since the first long-case grandfather clocks began marking off seconds in the mid-17th century and introduced the concept to the world at large.

The answer, simply, is that a second is 1/60th of a minute, or 1/360th of an hour. But that’s just pushing the question down the road a bit. After all, what’s an hour? That answer is related to the best means of time-keeping ancient civilizations had — the movement