Koordinoitu yleisaika

**Koordinoitu yleisaika** (**UTC**) on ensisijainen aikajärjestelmä, jolla maailman aika määrätään. Se pysyy noin sekunnin sisällä keskimääräisestä aurinkoajasta nollapituuspiirillä, eikä sitä ole sidottu kesäaikaan. Joissakin maissa termiä GMT (Greenwich Mean Time) käytetään yhä usein UTC:n synonyyminä. 

Ensimmäinen koordinoitu yleisaika hyväksyttiin epävirallisesti 1. tammikuuta 1960, mutta UTC:n virallinen lyhenne ja nimi hyväksyttiin vasta vuonna 1967.

## Lyhenteen alkuperä
Jos UTC-lyhenne otettaisiin suoraan englanninkielisistä sanoista *Coordinated Universal Time*, siitä tulisi CUT, ja jos se otettaisiin ranskankielisestä vastineesta *temps universel coordonné*, siitä tulisi TUC. Kansainvälinen televiestintäliitto kuitenkin halusi, että lyhenne ei viittaisi kumpaankaan kieleen, joten kompromissiksi valittiin UTC (Universal Time, Coordinated eli universel, temps coordonné).

## Aikavyöhykkeet

## Kirjallisuutta

* Allen, Steve (2011a). "UTC is doomed".
* Allen, Steve (2011b). "UTC might be redefined without Leap Seconds".
* Arias, E. F.; Guinot, B.; Quinn, T. J. (29 May 2003). Rotation of the Earth and Time scales (PDF). ITU-R Special Rapporteur Group Colloquium on the UTC Time Scale.
* "Aviation Time". AOPA's Path to Aviation. Aircraft Owners and Pilots Association. 2006.
* "Bulletin C". International Earth Rotation and Reference Systems Service. 6. heinäkuuta 2016.
* Essen, L. (1968). "Time Scales" (PDF). Metrologica. 4 (4): 161–5. Bibcode:1968Metro...4..161E. doi:10.1088/0026-1394/4/4/003.
* Finkleman, David; Allen, Steve; Seago, John; Seaman, Rob; Seidelmann, P. Kenneth (2011). "The Future of Time: UTC and the Leap Second". American Scientist. 99 (July–August 2011): 312. arXiv:1106.3141v1. doi:10.1511/2011.91.1.
* Guinot, Bernard (elokuussa 2011). "Solar time, legal time, time in use". Metrologica. 48 (4): S181–185. Bibcode:2011Metro..48S.181G. doi:10.1088/0026-1394/48/4/S08.
* "History of TAI-UTC". Time Service Dept., U.S. Naval Observatory. c. 2009.
* Horzepa, Stan (17. syyskuuta 2010). "Surfin': Time for Ham Radio". American Radio Relay League.
* Howse, Derek (1997). Greenwich Time and the Longitude. London: Philip Wilson. .
* "How NTP Works". NTP: The Network Time Protocol. 28 July 2011. See heading "NTP Timescale and Data Formats".
* "IAU resolutions adopted at the XVIth General Assembly, Grenoble, France, 1976" (PDF). 1976. Resolution no. 3 by Commissions 4 (Ephemerides/Ephémérides) and 31 (Time/L'Heure) (near the end of the document) "recommend that the following notations be used in all languages", UT0(i), UT1(i), UT2(i), UTC, UTC(i), UT, where (i) is institution "i".
* "Iceland". 2011.
* International Bureau of Weights and Measures (10. lokakuuta 2011). "Circular T" (285).
* International Earth Rotation and Reference Systems Service (19. heinäkuuta 2011). "IERS Bulletins".
* Irvine, Chris (18. joulukuuta 2008). "Scientists propose 'leap hour' to fix time system". The Telegraph.
* ITU Radiocommunication Assembly (2002). "Standard-frequency and time-signal emissions" (PDF). International Telecommunications Union.
* Langley, Richard B. (20. tammikuuta 1999). "A Few Facts Concerning GMT, UT, and the RGO".
* "Leap second decision is postponed". BBC News. 19. tammikuuta 2012.
* Markowitz, W.; Hall, R.; Essen, L.; Parry, J. (August 1958). "Frequency of caesium in terms of Ephemeris Time" (PDF). Physical Review Letters. 1 (3): 105–7. Bibcode:1958PhRvL...1..105M. doi:10.1103/PhysRevLett.1.105.
* Markowitz, Wm. (1988). "Comparisons of ET (Solar), ET (Lunar), UT and TDT". In Babcock, A. K.; Wilkins, G. A. The Earth's Rotation and Reference Frames for Geodesy and Geophysics: Proceedings of the 128th Symposium of the International Astronomical Union, held in Coolfont, West Virginia, U.S.A., 20–24 October 1986. Dordrecht: Kluwer Academic Publishers. pp. 413–418. Bibcode:1988IAUS..128..413M.
* McCarthy, Dennis D. (heinäkuussa 1991). "Astronomical Time" (PDF). Proc. IEEE. 79 (7): 915–920. doi:10.1109/5.84967.
* McCarthy, Dennis D.; Seidelmann, P. Kenneth (2009). TIME From Earth Rotation to Atomic Physics. Weinheim: Wiley VCH. .
* McCarthy, D.; Guinot, B. (2013). "Time". In Urban, Sean E.; Seidelmann, P. Kenneth. Explanatory Supplement to the Astronomical Almanac (3rd ed.). Mill Valley, CA: University Science Books.
* "Military & Civilian Time Designations". wwp.
* National Institute of Standards and Technology (18. tammikuuta 2011). "Frequently asked questions (FAQ)".
* National Institute of Standards and Technology (19. maaliskuuta 2012). "Frequently asked questions (FAQ)".
* Nelson, G.K.; Lombardi, M.A.; Okayama, D.T. (2005). "NIST Time and Frequency Radio Stations: WWV, WWVH, and WWVB" (PDF). National Institute of Standards and Technology. (Special Publication 250-67).
* Nelson, Robert A.; McCarthy, Dennis D. (13. syyskuuta 2005). Coordinated Universal Time (UTC) and the Future of the Leap Second. Civil GPS Interface Committee. United States Coast Guard.
* Nelson, Robert A.; McCarthy, Dennis D.; Malys, S.; Levine, J.; Guinot, B.; Fliegel, H. F.; Beard, R. L.; Bartholomew, T. R. (2001). "The leap second: its history and possible future" (PDF). Metrologia. 38 (6): 509–529. Bibcode:2001Metro..38..509N. doi:10.1088/0026-1394/38/6/6.
* Seidelmann, P. Kenneth; Seago, John H. (elokuussa 2011). "Time scales, their users, and leap seconds". Metrologia. 48 (4): S186–S194. Bibcode:2011Metro..48S.186S. doi:10.1088/0026-1394/48/4/S09.
* Seaman, Rob (2003). "A Proposal to Upgrade UTC".
* Seidelmann, P Kenneth, ed. (1992). Explanatory Supplement to the Astronomical Almanac (2nd ed.). Mill Valley, CA: University Science Books. .
* Stephenson, F. R.; Morrison, L. V. (1995). "Long-term fluctuations in the Earth's rotation: 700 BC to AD 1990". Philosophical Transactions of the Royal Society A. 351 (1695): 165–202. Bibcode:1995RSPTA.351..165S. doi:10.1098/rsta.1995.0028.
* "Standard time". U.S. Code. Legal Information Institute. 2010. Title 15, Chapter 6, Subchapter IX.
* "TF.460-4: Standard-frequency and time-signal emissions" (PDF). International Telecommunication Union. 1986. Annex I.
* "Time". International Bureau of Weights and Measures. n.d.
* Time Service Dept. (2016). "Leap Seconds". United States Naval Observatory.
* United States Naval Observatory. "Universal Time".
* "Universal Time". Oxford Dictionaries: British and World English. Oxford University Press.
* Williams, Jack (17. toukokuuta 2005). "Understanding and using Zulu time". USA Today.

## Lähteet