Wonderful Engineering

Ever Wondered How Was The Length Of A Second First Determined? Here’s The Answer

Have you ever wondered who decided how long a second was and how? How was it first measured?

With the invention of clocks, finer divisions of time allowed time to be measured in not just days and hours but also minutes and seconds. In Latin, a minute was known as pars minuta prima – ‘the first very small part’  and the second was called the pars minuta Secunda – ‘the second very small part’.

Following the tradition set by the Babylonians, these divisions were expressed using the sexagesimal system, a form of counting based on units of 60. Using this, the length of a second became a sixtieth of a sixtieth of an hour, leading to its definition as 1/3600th of an hour.

Following the tradition set by the Babylonians, the divisions in time were based on the sexagesimal system, a form of counting based on units of 60. According to this system, the length of a minute was a sixtieth of an hour  (one hour thus has 60 minutes) and the second was a sixtieth of a sixtieth of an hour (one hour thus has 3600 seconds). This lead to the definition of a second to be 1/3600 of an hour.
Later, a  scientific method to measure a second was adopted and is the one currently in place. The scientific definition of the second, as per the International System of Units is as follows:
One second is the time that elapses during 9,192,631,770 cycles of the radiation produced by the transition between two levels of the cesium 133 atom.