Seconds (s)
The second is the SI base unit of time, defined by the duration of 9,192,631,770 periods of radiation from the transition between two hyperfine levels of the cesium-133 atom. Exactly 1 second equals this duration according to the International System of Units (SI) standard [bipm-si-brochure]. It provides the fundamental unit for time measurement in science and industry worldwide.
Origin
The second was originally defined as 1/86,400 of a mean solar day but was redefined in 1967 by the International Committee for Weights and Measures based on atomic properties to improve precision [bipm-si-brochure]. This atomic definition replaced astronomical definitions to ensure stability and reproducibility.
Worldwide Use
The second is used globally as the standard time unit in scientific research, telecommunications, navigation, and everyday timekeeping. It is adopted by international standards organizations including ISO and NIST [nist-si-guide].
Common References
- A typical heartbeat interval is about 1 second
- The duration of one second in digital clocks
- The time between traffic light changes
- One second for a stopwatch lap
- The delay in internet data transmission is often measured in milliseconds (thousandths of a second)