Second

The second (s) is the unit of time (t). The concept is based on the Sumerian hexagesimal numeral system (third millennium BC), but the name is derived from the Latin expression pars minuta secunda, meaning "second diminished part". This expression goes back to the Persian scholar Abu Rayhan al-Biruni (973 – 1048).

The second is defined by the duration of 9,192,631,770 cycles of the radiation emitted by the ¹³³Cs atomic clock.

History

Originally, a second is a 60th part of a minute, which in turn is a 60th part of an hour, while an hour is a 24th part of a solar day. In ancient times, the time of day was indicated using a sundial, invented by the Egyptians and Mesopotamians. The oldest sundials were obelisks (3500 BC).

Only after the invention of the pendulum clock around 1656 by the Dutch scholar Christiaan Huygens (1629 – 1695) did reliable time measurements become feasible. The first pendulum clock was made by the Hague clockmaker Salomon Coster (1622 – 1659).

Related concepts

• base units
• centimeter
• electronvolt
• erg
• gram
• joule
• kilogram
• meter
• watt