Science has several different ways of defining time. To cover just a couple: There’s astronomical time, which is measured by how long it takes Earth to rotate on its axis. In astronomical time, a second is 1/60th of a minute. And then there’s atomic time, which dictates the numbers that you’ll see on a clock. According to atomic time, one second equals 9,192,631,770 oscillations of a cesium-133 atom. Measuring the vibration of an atom—which, in simple terms, is the gist of what oscillation is—is the most accurate way to track time.