# second

> SI unit of time, defined as 9 192 631 770 periods of the ground-state hyperfine transitions of caesium-133

**Wikidata**: [Q11574](https://www.wikidata.org/wiki/Q11574)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Second)  
**Source**: https://4ort.xyz/entity/second


## References

1. ISO 80000-1:2009 Quantities and units—Part 1: General
2. [Time and frequency: SI unit of time (second). International Bureau of Weights and Measures](https://www.bipm.org/metrology/time-frequency/units.html)
3. SI Brochure (9th edition): Concise summary
4. Freebase Data Dumps. 2013
5. [Time and frequency: SI unit of time (second) (inglés). International Bureau of Weights and Measures](https://www.bipm.org/metrology/time-frequency/units.html)
6. [Source](https://www.wikidata.org/wiki/Special:ListDatatypes#Time)
7. Logopedia
8. ISO 80000-3:2006 Quantities and units — Part 3: Space and time
9. GF WordNet