TIME

Since the dawn of humanity, the sky and the movement of its celestial bodies have dictated the base for all time measurement. Day and night, seasons, the year, the calendar, and of course the hour: all notions of time are regulated by the motion of the stars. 

Sexagesimal system

For religious reasons, the Babylonians divided the night into three, then six, then twelve equal periods, using equidistant stars in the celestial vault observable every night of the year as a reference. The twelve hours of the night were doubled to make the day, resulting in 24 hours. It was the Sumerians who, in 3000 BCE, invented the sexagesimal system (base 60). This calculation base would later be used by the Babylonians before spreading throughout Mesopotamia. And this is how the sexagesimal system became established in time measurement as well as in astronomy and geometry.

The second: the base unit for measuring time

The second has been the standard unit of time since 1889. It was first defined by dividing the hour into 60 minutes, which was divided into 60 seconds. Since 1967, the second has been defined as a multiple of the frequency of Caesium 133 (9,192,631,770 Hz). The minute and the hour have thus become multiples of this standard second.

The International Bureau of Weights and Measures (BIPM) now calculates the atomic second by averaging several hundred atomic clocks distributed across various laboratories and observatories around the world. New generations of optical frequency atomic clocks use different atoms, which significantly increase their precision to reach a deviation rate of one second in 13 billion years. Such clocks could soon redefine the standard second of the International System of Units (SI).

In the past, the second was divided into 60 equal periods called “thirds.” Today, for practical reasons, the second is divided according to the decimal system.

The second: a unit for measuring distance

In watchmaking, the second and its divisions are the universally used units. Beyond timekeeping, the precision of the second and its subdivisions are crucial to most scientific fields. Due to the precision achieved in time measurement, the second has become a unit of distance measurement. The standard metre is defined by the distance travelled by light in 1/299,792,458 of a second. Thus, time is used to define distance.