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Topic: International Atomic Time

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In the News (Thu 25 Apr 19)

  Leap Seconds
Coordinated Universal Time (UTC), an atomic time, is the basis for civil time.
International Atomic Time (TAI) is a statistical atomic time scale based on a large number of clocks operating at standards laboratories around the world that is maintained by the Bureau International des Poids et Mesures; its unit interval is exactly one SI second at sea level.
Terrestrial Time (TT) is a uniform atomic time scale, whose unit is the SI second, that replaces Ephemeris Time and maintains continuity with it.
tycho.usno.navy.mil /leapsec.html   (1741 words)

 Systems of Time   (Site not responding. Last check: 2007-10-19)
Atomic Time, with the unit of duration the Systeme International (SI) second defined as the duration of 9,192,631,770 cycles of radiation corresponding to the transition between two hyperfine levels of the ground state of cesium 133.
Universal Time (UT) is counted from 0 hours at midnight, with unit of duration the mean solar day, defined to be as uniform as possible despite variations in the rotation of the Earth.
Sidereal Time, with unit of duration the period of the Earth's rotation with respect to a point nearly fixed with respect to the stars, is the hour angle of the vernal equinox.
tycho.usno.navy.mil /systime.html   (560 words)

 International Atomic Time - Wikipedia, the free encyclopedia
Time coordinates on the TAI scales are conventionally specified using traditional means of specifying days, carried over from non-uniform time standards based on the rotation of the Earth.
This was a compromise arrangement for a broadcast time scale: a linear transformation of the BIH's atomic time meant that the time scale was stable and internationally synchronised, while approximating UT1 means that tasks such as navigation which require a source of Universal Time continue to be well served by public time broadcasts.
In the 1970s it became clear that the clocks participating in TAI were ticking at different rates due to gravitational time dilation, and the combined TAI scale therefore corresponded to an average of the altitudes of the various clocks.
en.wikipedia.org /wiki/International_Atomic_Time   (1091 words)

 International standard date and time notation
A single leap second 23:59:60 is inserted into the UTC time scale every few years as announced by the International Earth Rotation Service in Paris, to keep UTC from wandering away more than 0.9 s from the less constant astronomical time scale UT1, which is defined by the actual rotation of the earth.
In case an unambiguous representation of time is required, 00:00 is usually the preferred notation for midnight and not 24:00.
Please consider the 12h time to be a relic from the dark ages when Roman numerals were used, the number zero had not yet been invented and analog clocks were the only known form of displaying a time.
www.cl.cam.ac.uk /~mgk25/iso-time.html   (2932 words)

 BIPM - time
International Atomic Time (TAI) is the uniform time scale; it is kept as close as possible to the second of the SI.
Coordinated Universal Time (UTC) is an atomic time scale derived from TAI, to provide a reference scale in step with the irregular rotation of the earth.
Other activities related to the time scales are developed in the section; these contribute to improving the calculation algorithms and increasing knowledge about time transfer techniques.
www.bipm.fr /enus/5_Scientific/c_time/time_1.html   (252 words)

 International Atomic Time - Search Results - MSN Encarta   (Site not responding. Last check: 2007-10-19)
International Atomic Time - Search Results - MSN Encarta
- time-measuring system: a precisely determined system of measuring time in which a second is defined in terms of atomic events that are known to a high degree of accuracy
The cesium-atom clock is used to define the second, the basic unit of time of the International System of Units.
encarta.msn.com /International_Atomic_Time.html   (227 words)

 IERS Glossary: International Atomic Time (TAI)
It is calculated by the BIPM from the readings of more than 200 atomic clocks located in metrology institutes and observatories in more than 30 countries around the world.
BIPM estimates that TAI does not lose or gain with respect to an imaginary perfect clock by more than about one tenth of a microsecond (0.0000001 second) per year.
TAI is a continues time scale which is not connected to Earth rotation.
www.iers.org /iers/earth/glossary/tai.html   (107 words)

 BIPM - approximation to UTC
Coordinated Universal Time (UTC), maintained by the BIPM, is the time scale that forms the basis for the coordinated dissemination of standard frequencies and time signals.
The UTC scale is adjusted by the insertion of leap seconds to ensure approximate agreement with the time derived from the rotation of the Earth.
The time displayed here is for demonstration only, and should not be used as a standard.
www.bipm.org /en/scientific/tai/time_server.html   (152 words)

 BIPM - International Atomic Time
A practical scale of time for world-wide use has two essential elements: a realization of the unit of time and a continuous temporal reference.
The reference used is International Atomic Time (TAI), a time scale calculated at the BIPM using data from some two hundred atomic clocks in over fifty national laboratories.
Such a scale is Coordinated Universal Time (UTC), which is identical with TAI except that from time to time a leap second is added to ensure that, when averaged over a year, the Sun crosses the Greenwich meridian at noon UTC to within
www.bipm.fr /en/scientific/tai/tai.html   (234 words)

 International Atomic Energy Agency (IAEA)
International Conference on Non-Electric Applications of Nuclear Power: Seawater Desalination, Hydrogen Production and other Industrial Applications, Oarai, Japan
International Conference on the Challenges faced by Technical and Scientific Support Organizations in Enhancing Nuclear Safety, Aix-en-Provence, France
Copyright 2003-2006, International Atomic Energy Agency, P.O. Box 100, Wagramer Strasse 5, A-1400 Vienna, Austria
www.iaea.org   (344 words)

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