3674:
294:, does not keep uniform time. The time kept by a sundial varies by time of year, meaning that seconds, minutes and every other division of time is a different duration at different times of the year. The time of day measured with mean time versus apparent time may differ by as much as 15 minutes, but a single day differs from the next by only a small amount; 15 minutes is a cumulative difference over a part of the year. The effect is due chiefly to the obliqueness of Earth's axis with respect to its
3668:
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378:. Though many derivative units for everyday things are reported in terms of larger units of time, not seconds, they are ultimately defined in terms of the SI second; this includes time expressed in hours and minutes, velocity of a car in kilometers per hour or miles per hour, kilowatt hours of electricity usage, and speed of a turntable in rotations per minute.
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38:
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phenomena of nature. The current generation of atomic clocks is accurate to within one second in a few hundred million years. Since 1967, atomic clocks based on atoms other than caesium-133 have been developed with increased precision by a factor of 100. Therefore a new definition of the second is planned.
479:, in the red range of visible light, during the 2010s held the accuracy record: it gains or loses less than a second in 15 billion years, which is longer than the estimated age of the universe. Such a clock can measure a change in its elevation of as little as 2 cm by the change in its rate due to
970:
The CIPM has adopted various secondary representations of the second, based on a selected number of spectral lines of atoms, ions or molecules. The unperturbed frequencies of these lines can be determined with a relative uncertainty not lower than that of the realization of the second based on the Cs
664:
Sometime in the late 1940s, quartz crystal oscillator clocks with an operating frequency of ~100 kHz advanced to keep time with accuracy better than 1 part in 10 over an operating period of a day. It became apparent that a consensus of such clocks kept better time than the rotation of the Earth.
992:
In 2022, the best realisation of the second is done with caesium primary standard clocks such as IT-CsF2, NIST-F2, NPL-CsF2, PTB-CSF2, SUâCsFO2 or SYRTE-FO2. These clocks work by laser-cooling a cloud of Cs atoms to a microkelvin in a magneto-optic trap. These cold atoms are then launched vertically
946:
In a laboratory sufficiently small to allow the effects of the non-uniformity of the gravitational field to be neglected when compared to the uncertainties of the realization of the second, the proper second is obtained after application of the special relativistic correction for the velocity of the
936:
The definition of a unit refers to an idealized situation that can be reached in the practical realization with some uncertainty only. In this spirit, the definition of the second has to be understood as referring to atoms free of any perturbation, at rest and in the absence of electric and magnetic
563:
The earliest mechanical clocks, which appeared starting in the 14th century, had displays that divided the hour into halves, thirds, quarters and sometimes even 12 parts, but never by 60. In fact, the hour was not commonly divided in 60 minutes as it was not uniform in duration. It was not practical
924:
At its 1997 meeting, the CIPM affirmed that: This definition refers to a caesium atom at rest at a temperature of 0 K. This note was intended to make it clear that the definition of the SI second is based on a Cs atom unperturbed by black-body radiation, that is, in an environment whose temperature
728:
Even the best mechanical, electric motorized and quartz crystal-based clocks develop discrepancies from environmental conditions; far better for timekeeping is the natural and exact "vibration" in an energized atom. The frequency of vibration (i.e., radiation) is very specific depending on the type
337:
Some common events in seconds are: a stone falls about 4.9 meters from rest in one second; a pendulum of length about one meter has a swing of one second, so pendulum clocks have pendulums about a meter long; the fastest human sprinters run 10 meters in a second; an ocean wave in deep water travels
966:
The second, so defined, is the unit of proper time in the sense of the general theory of relativity. To allow the provision of a coordinated time scale, the signals of different primary clocks in different locations are combined, which have to be corrected for relativistic caesium frequency shifts
238:
to denote subdivisions of the second: milliseconds (thousandths), microseconds (millionths), nanoseconds (billionths), and sometimes smaller units of a second. Multiples of seconds are usually counted in hours and minutes. Though SI prefixes may also be used to form multiples of the second such as
269:
divisions of the day from a calendar based on astronomical observation have existed since the third millennium BC, though they were not seconds as we know them today. Small divisions of time could not be measured back then, so such divisions were mathematically derived. The first timekeepers that
920:
This definition implies that the caesium atom is at rest and unperturbed. In consequence, in its practical realization, measurements must be corrected for velocity of the atoms with respect to the clock reference frame, for magnetic and electric fields including ambient black-body radiation, for
301:
The difference between apparent solar time and mean time was recognized by astronomers since antiquity, but prior to the invention of accurate mechanical clocks in the mid-17th century, sundials were the only reliable timepieces, and apparent solar time was the only generally accepted standard.
310:
Fractions of a second are usually denoted in decimal notation, for example 2.01 seconds, or two and one hundredth seconds. Multiples of seconds are usually expressed as minutes and seconds, or hours, minutes and seconds of clock time, separated by colons, such as 11:23:24, or 45:23 (the latter
741:
atom". This length of a second was selected to correspond exactly to the length of the ephemeris second previously defined. Atomic clocks use such a frequency to measure seconds by counting cycles per second at that frequency. Radiation of this kind is one of the most stable and reproducible
579:
The earliest clocks to display seconds appeared during the last half of the 16th century. The second became accurately measurable with the development of mechanical clocks. The earliest spring-driven timepiece with a second hand that marked seconds is an unsigned clock depicting
311:
notation can give rise to ambiguity, because the same notation is used to denote hours and minutes). It rarely makes sense to express longer periods of time like hours or days in seconds, because they are awkwardly large numbers. For the metric unit of second, there are
1194:
1043:, or even higher. They have better stabilities than microwave clocks, which means that they can facilitate evaluation of lower uncertainties. They also have better time resolution, which means the clock "ticks" faster. Optical clocks use either a single ion, or an
612:
invented the first pendulum clock. It had a pendulum length of just under a meter, giving it a swing of one second, and an escapement that ticked every second. It was the first clock that could accurately keep time in seconds. By the 1730s, 80 years later,
1771:
It may be noted that 60 is the smallest multiple of the first 6 counting numbers. So a clock with 60 divisions would have a mark for thirds, fourths, fifths, sixths and twelfths (the hours); whatever units the clock would likely keep time in, would have
695:, considered more fundamental than the sidereal year, was chosen by the IAU as the unit of time. The tropical year in the definition was not measured but calculated from a formula describing a mean tropical year that decreased linearly over time.
1281:
A redefinition must include improved optical clock reliability. TAI must be contributed to by optical clocks before the BIPM affirms a redefinition. A consistent method of sending signals must be developed before the second is redefined, such as
604:
redesigned clocks that had displayed only minutes at his observatory so they also displayed seconds, even though those seconds were not accurate. In 1587, Tycho complained that his four clocks disagreed by plus or minus four seconds.
1264:
The only viable way to fix the
Rydberg constant involves trapping and cooling hydrogen. This is difficult because it is very light and the atoms move very fast, causing Doppler shifts. The radiation needed to cool the hydrogen â
962:
The reference to an unperturbed atom is intended to make it clear that the definition of the SI second is based on an isolated caesium atom that is unperturbed by any external field, such as ambient black-body radiation.
1001:
systematic uncertainty, which is equivalent to 50 picoseconds per day. A system of several fountains worldwide contribute to
International Atomic Time. These caesium clocks also underpin optical frequency measurements.
509:
Civilizations in the classic period and earlier created divisions of the calendar as well as arcs using a sexagesimal system of counting, so at that time the second was a sexagesimal subdivision of the day (ancient
239:
kiloseconds (thousands of seconds), such units are rarely used in practice. An everyday experience with small fractions of a second is a 1-gigahertz microprocessor that has a cycle time of 1 nanosecond. Camera
2446:
942:
The definition of the second should be understood as the definition of the unit of proper time: it applies in a small spatial domain that shares the motion of the caesium atom used to realize the definition.
227:
often have sixty tick marks on their faces, representing seconds (and minutes), and a "second hand" to mark the passage of time in seconds. Digital clocks and watches often have a two-digit seconds counter.
286:, within whatever accuracy is intrinsic to it. That means that every second, minute and every other division of time counted by the clock has the same duration as any other identical division of time. But a
818:
552:). Sundials and water clocks were among the earliest timekeeping devices, and units of time were measured in degrees of arc. Conceptual units of time smaller than realisable on sundials were also used.
1259:
555:
There are references to "second" as part of a lunar month in the writings of natural philosophers of the Middle Ages, which were mathematical subdivisions that could not be measured mechanically.
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679:(1895), which provided a formula for estimating the motion of the Sun relative to the epoch 1900 based on astronomical observations made between 1750 and 1892. This resulted in adoption of an
3572:
435:
A set of atomic clocks throughout the world keeps time by consensus: the clocks "vote" on the correct time, and all voting clocks are steered to agree with the consensus, which is called
338:
about 23 meters in one second; sound travels about 343 meters in one second in air; light takes 1.3 seconds to reach Earth from the surface of the Moon, a distance of 384,400 kilometers.
4954:
471:
While they are not yet part of any timekeeping standard, optical lattice clocks with frequencies in the visible light spectrum now exist and are the most accurate timekeepers of all. A
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849:
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also knew that Earth's orbit around the Sun (a year) was much more stable than Earth's rotation. This led to proposals as early as 1950 to define the second as a fraction of a year.
925:
is 0 K, and that the frequencies of primary frequency standards should therefore be corrected for the shift due to ambient radiation, as stated at the meeting of the CCTF in 1999.
909:
The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom
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1949:
629:
904:
1033:
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in 1952. This extrapolated timescale brings the observed positions of the celestial bodies into accord with
Newtonian dynamical theories of their motion. In 1955, the
371:
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1981:
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That according to the decisions of the 8th
General Assembly of the International Astronomical Union (Rome, 1952), the second of ephemeris time (ET) is the fraction
564:
for timekeepers to consider minutes until the first mechanical clocks that displayed minutes appeared near the end of the 16th century. Mechanical clocks kept the
318:
Some common units of time in seconds are: a minute is 60 seconds; an hour is 3,600 seconds; a day is 86,400 seconds; a week is 604,800 seconds; a year (other than
2149:
993:
by laser light. The atoms then undergo Ramsey excitation in a microwave cavity. The fraction of excited atoms is then detected by laser beams. These clocks have
457:. UT1 is defined by the rotation of the Earth with respect to the Sun, and does not contain any leap seconds. UT1 always differs from UTC by less than a second.
2462:
2287:
497:
There have only ever been three definitions of the second: as a fraction of the day, as a fraction of an extrapolated year, and as the microwave frequency of a
959:, the unperturbed ground-state hyperfine transition frequency of the caesium 133 atom, to be 9 192 631 770 when expressed in the unit Hz, which is equal to s.
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units. Both the CGS and MKS systems used the same second as their base unit of time. MKS was adopted internationally during the 1940s, defining the second as
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A future re-definition of the second would be justified if these idealized conditions can be achieved much easier than with the current definition.
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632:(BAAS) in 1862 stated that "All men of science are agreed to use the second of mean solar time as the unit of time." BAAS formally proposed the
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of the caesium 133 atom, unperturbed by external fields, and that the frequency of this transition is assigned the value 9192631770 hertz.
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This current definition was adopted in 1967 when it became feasible to define the second based on fundamental properties of nature with
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A mechanical clock, which does not depend on measuring the relative rotational position of the Earth, keeps uniform time called
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1700:, which includes leap seconds. Other time scales are used in scientific and technical fields that do not contain leap seconds.
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57:
673:
1189:{\displaystyle R_{\infty }={\frac {m_{\text{e}}e^{4}}{8\varepsilon _{0}^{2}h^{3}c}}={\frac {m_{\text{e}}c\alpha ^{2}}{2h}}}
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The second, symbol s, is the SI unit of time. It is defined by taking the fixed numerical value of the caesium frequency, Î
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The standard to be employed is the transition between the hyperfine levels F=4, M=0 and F=3, M=0 of the ground state
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of atom and how it is excited. Since 1967, the second has been defined as exactly "the duration of 9,192,631,770
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206:, meaning "first small part" i.e. first division of the hour - dividing into sixty, and "second" comes from the
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of certain specific weeks as a number of days, hours, minutes, seconds, thirds, and fourths after noon Sunday.
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atomic clock, which have each realized a sexagesimal division of the day from ancient astronomical calendars.
1269:â is also difficult. Another hurdle involves improving the uncertainty in QED calculations, specifically the
1196:. The Rydberg constant describes the energy levels in a hydrogen atom with the nonrelativistic approximation
442:
Civil time is defined to agree with the rotation of the Earth. The international standard for timekeeping is
370:, a measure of radioactive decay, is measured in inverse seconds and higher powers of second are involved in
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are commonly used for times shorter than one second, but rarely for multiples of a second. Instead, certain
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could count seconds accurately were pendulum clocks invented in the 17th century. Starting in the 1950s,
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full page color photo: 4th caption page, 3rd photo thereafter (neither pages nor photos are numbered).
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Explanatory
Supplement to the Astronomical Ephemeris and the American Ephemeris and Nautical Almanac
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also depend on the second. The only base unit whose definition does not depend on the second is the
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Philosophical
Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
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Philosophical
Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
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Philosophical
Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
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Reprinted from the "IAU Style Manual" by G.A. Wilkinson, Comm. 5, in IAU Transactions XXB (1987).
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the footnote was added at the 86th (1997) meeting of the CIPM GCPM 1998 7th
Edition SI Brochure
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footnote added by the 14th meeting of the
Consultative Committee for Time and Frequency in 1999
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became better timekeepers than Earth's rotation, and they continue to set the standard today.
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National Physical Laboratory (2011). "When should we change the definition of the second?".
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A time scale in which the seconds are not exactly equal to atomic seconds is UT1, a form of
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are based on forbidden optical transitions in ions or atoms. They have frequencies around
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Encyclopaedia of the History of Science, Technology, and Medicine in Non-Western Cultures
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Nautical Almanac Offices of the United Kingdom and the United States of America (1961),
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resolved in 2018 effective after the 26th GCPM approved the redefinition May 20, 2019.
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326:) century averages 3,155,695,200 seconds; with all of the above excluding any possible
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proposed using the second as the base unit of time in his millimeterâmilligramâsecond
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The second is defined by taking the fixed numerical value of the caesium frequency, Î
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hyperfine transition frequency, but some can be reproduced with superior stability.
617:'s maritime chronometers could keep time accurate to within one second in 100 days.
446:(UTC). This time scale "ticks" the same atomic seconds as TAI, but inserts or omits
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atom in the laboratory. It is wrong to correct for the local gravitational field.
393:(in vacuum) to be 299 792 458 m/s, exactly; definitions of the SI base units
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1942:"The most accurate clock ever built only loses one second every 15 billion years"
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576:. By that time, sexagesimal divisions of time were well established in Europe.
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in 1874, although this system was gradually replaced over the next 70 years by
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as necessary to correct for variations in the rate of rotation of the Earth.
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at 12 hours ephemeris time". This definition was adopted as part of the
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In 1956, the second was redefined in terms of a year relative to that
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2273:; Seidelmann, P. Kenneth (2009). "Definition and Role of a Second".
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of the tropical year for 1900 January 0 at 12 hours ephemeris time.
290:, which measures the relative position of the Sun in the sky called
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2148:. British Association for the Advancement of Science. p. 90.
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19:
This article is about the unit of clock time. For other uses, see
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of the radiation corresponding to the transition between the two
118:â this factor derived from the division of the day first into 24
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813:{\displaystyle {\frac {12960276813}{408986496}}\times 10^{-9}}
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180:. Because the speed of Earth's rotation varies and is slowing
115:
1742:
as a number of hours, minutes, seconds, thirds, and fourths (
4720:
1254:{\displaystyle E_{n}\approx -{\frac {R_{\infty }ch}{n^{2}}}}
921:
spin-exchange effects and for other possible perturbations.
4242:
2475:; notice the cesium atom must be in its ground state at 0 K
62:
3573:
International Earth Rotation and Reference Systems Service
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SLAC: Scales of Time â Our universe from 10 to 10 seconds
1738:, writing in Latin, defined the division of time between
2465:
Optical frequency standard based on a single trapped ion
126:
and finally to 60 seconds each (24 Ă 60 Ă 60 = 86400).
2501:
2106:. Springer Science & Business Media. p. 934.
2046:. Cambridge, Massachusetts: Harvard University Press.
820:
of the tropical year for 1900 January 0 at 12 h ET.
584:
in the Fremersdorf collection, dated between 1560 and
366:
in meters per second squared. The metric system unit
243:
are often expressed in fractions of a second, such as
2360:"When should we change the definition of the second?"
1980:. Translated by Sachau, C. Edward. pp. 147â149.
1835:"When should we change the definition of the second?"
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Atomic clocks now set the length of a second and the
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are defined by their relationship to the second: the
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built a clock with marks every 1/5 minute. In 1579,
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843:
812:
630:British Association for the Advancement of Science
346:A second is directly part of other units, such as
212:, "second small part", dividing again into sixty.
2485:The leap second: its history and possible future
2145:Reports of the committee on electrical standards
2214:... defined ephemeris time ... adopted by the
1917:
1915:
1913:
1911:
702:. The second was thus defined as "the fraction
1273:in the 1s-2s transition of the hydrogen atom.
505:Sexagesimal divisions of calendar time and day
413:, and only two of the 22 named derived units,
192:to keep clocks in sync with Earth's rotation.
4736:
4603:
4258:
3489:
2517:
8:
2294:in November 2022, Section E, p. 25
1891:"mathematics â Ancient mathematical sources"
588:During the 3rd quarter of the 16th century,
533:), not of the hour like the modern second (=
4549:Historical definitions of the SI base units
2275:Time: From Earth Rotation to Atomic Physics
1927:Time: From Earth Rotation to Atomic Physics
1721:, and defined the division of time between
207:
201:
4743:
4729:
4721:
4610:
4596:
4588:
4265:
4251:
4243:
3496:
3482:
3474:
3207:
2581:
2524:
2510:
2502:
2292:General Conference on Weights and Measures
1455:11 days, 13 hours, 46 minutes, 40 seconds
1304:non-SI units are permitted for use with SI
844:{\displaystyle {\frac {1}{31556925.9747}}}
36:
27:
2456:High-accuracy strontium ion optical clock
2383:
2032:
2030:
2028:
1858:
1762:) after noon on specified calendar dates.
1243:
1226:
1219:
1207:
1201:
1169:
1156:
1149:
1134:
1124:
1119:
1104:
1094:
1087:
1078:
1072:
1017:
886:
882:
872:
867:
831:
829:
801:
784:
782:
129:The current and formal definition in the
4027:International Commission on Stratigraphy
1734:In 1267, the medieval English scientist
1324:
756:
2449:Trapped ion optical frequency standards
2171:
2169:
2167:
1984:from the original on September 16, 2019
1785:
1686:
4955:Centimetreâgramâsecond system of units
2480:Official BIPM definition of the second
2353:
2351:
2152:from the original on November 20, 2016
2120:from the original on November 20, 2016
421:, do not depend on the second either.
234:are frequently combined with the word
2463:National Research Council of Canada:
2458:; National Physical Laboratory (2005)
1952:from the original on January 27, 2018
7:
3458:
2007:. translated by Robert Belle Burke.
672:The Earth's motion was described in
2187:from the original on March 12, 2015
1717:, writing in Arabic, used the term
1696:is set, directly or indirectly, to
439:(TAI). TAI "ticks" atomic seconds.
306:Events and units of time in seconds
188:is added at irregular intervals to
2417:"Recommendations Concerning Units"
2415:International Astronomical Union.
2358:Gill, Patrick (October 28, 2011).
1833:Gill, Patrick (October 28, 2011).
1227:
1079:
1019:
467:Atomic clock § Optical clocks
14:
3747:Discrete time and continuous time
1977:The chronology of ancient nations
1940:Vincent, James (April 22, 2015).
1925:; Seidelmann, P. Kenneth (2009).
1814:from the original on May 23, 2019
342:Other units incorporating seconds
334:is precisely 31,557,600 seconds.
4572:
4571:
3672:
3666:
3457:
3448:
3447:
2251:from the original on May 3, 2019
2216:International Astronomical Union
2009:University of Pennsylvania Press
683:scale expressed in units of the
322:) is 31,536,000 seconds; and a (
46:of a clock, ticking every second
2181:United States Naval Observatory
1035:of typically 1 Hz, so the
315:representing 10 to 10 seconds.
4559:System of units of measurement
3820:History of timekeeping devices
2447:National Physical Laboratory:
2140:Jenkin, Henry Charles Fleeming
712:of the tropical year for 1900
600:that marked seconds. In 1581,
493:History of timekeeping devices
475:clock with frequency 430
200:"Minute" comes from the Latin
104:(SI), historically defined as
1:
2005:The Opus Majus of Roger Bacon
718:International System of Units
654:Fraction of an ephemeris year
131:International System of Units
102:International System of Units
2491:What is a Cesium atom clock?
2067:Willsberger, Johann (1975).
1326:SI multiples for second (s)
856:11th CGPM 1960 Resolution 9
151:transition frequency of the
4619:Orders of magnitude of time
3767:Gravitational time dilation
3603:Barycentric Coordinate Time
3262:Geological history of Earth
2179:. Time Service Department,
1012:, with a natural linewidth
899:{\displaystyle ^{2}S_{1/2}}
824:The second is the fraction
737:of the ground state of the
481:gravitational time dilation
372:derivatives of acceleration
168:when expressed in the unit
4988:
4960:Orders of magnitude (time)
3623:Geocentric Coordinate Time
3608:Barycentric Dynamical Time
3546:Coordinated Universal Time
2614:Orders of magnitude (time)
1698:Coordinated Universal Time
1665:Orders of magnitude (time)
1333:
1295:Orders of magnitude (time)
1292:
1063:A definition based on the
657:
490:
464:
444:Coordinated Universal Time
428:
389:is defined by setting the
362:in meters per second, and
18:
4625:
4567:
3777:Time-translation symmetry
3664:
3588:International Atomic Time
3515:
3443:
3325:Time translation symmetry
2011:. table facing page 231.
1335:
1330:
759:
608:In 1656, Dutch scientist
437:International Atomic Time
35:
4513:minute and second of arc
2473:Definition of the second
2075:. New York: Dial Press.
1028:{\displaystyle \Delta f}
760:Evolution of the Second
4554:2019 revision of the SI
4037:Astronomical chronology
4010:Archaeology and geology
3717:Absolute space and time
3633:IERS Reference Meridian
3628:International Date Line
3539:International standards
3280:Absolute space and time
2931:Astronomical chronology
2238:SI Brochure 8th Edition
1895:Encyclopedia Britannica
1624:31.7 quintillion years
1601:31.7 quadrillion years
1430:16 minutes, 40 seconds
912:13th CGPM Resolution 1
768:Resolution of the CGPM
21:Second (disambiguation)
3330:Time reversal symmetry
2634:Italian six-hour clock
2385:10.1098/rsta.2011.0237
2326:10.1098/rsta.2011.0237
2003:Bacon, Roger (2000) .
1860:10.1098/rsta.2011.0237
1647:31.7 sextillion years
1255:
1190:
1029:
900:
845:
814:
765:Decisions of the CIPM
208:
202:
174:
172:, which is equal to s.
4710:terasecond and longer
3996:Weekday determination
3882:Sundial markup schema
3095:Time and fate deities
3040:The Unreality of Time
2979:A series and B series
1405:1 minute, 40 seconds
1256:
1191:
1030:
967:(see section 2.3.6).
901:
846:
815:
687:at that epoch by the
650:of a mean solar day.
559:Fraction of solar day
487:History of definition
461:Optical lattice clock
425:Timekeeping standards
381:Moreover, most other
278:Clocks and solar time
135:
133:(SI) is more precise:
4785:Derived non EM units
4455:Other accepted units
4017:Chronological dating
3757:Theory of relativity
3618:Daylight saving time
3346:Chronological dating
3315:Theory of relativity
2659:Daylight saving time
2423:on February 16, 2007
2231:"SI Brochure (2006)"
2071:Clocks & watches
1794:"SI Brochure (2019)"
1578:31.7 trillion years
1200:
1071:
1016:
866:
828:
781:
568:, as opposed to the
42:A pendulum-governed
4539:Conversion of units
4227:Time value of money
4022:Geologic time scale
3877:History of sundials
3742:Cosmological decade
3694:Greenwich Mean Time
3525:Orders of magnitude
2639:Thai six-hour clock
2376:2011RSPTA.369.4109G
2370:(1953): 4109â4130.
2318:2011RSPTA.369.4109G
2312:(1953): 4109â4130.
2271:McCarthy, Dennis D.
1923:McCarthy, Dennis D.
1851:2011RSPTA.369.4109G
1845:(1953): 4109â4130.
1555:31.7 billion years
1530:31.7 million years
1327:
1318:, and in astronomy
1129:
988:Future redefinition
209:pars minuta secunda
52:General information
4332:with special names
4202:Mental chronometry
3830:Marine chronometer
3682:Obsolete standards
3169:Rosy retrospection
3147:Mental chronometry
2971:Philosophy of time
2277:. Weinheim: Wiley.
2043:Revolution in Time
1929:. Weinheim: Wiley.
1325:
1251:
1186:
1115:
1025:
976:Current Definition
896:
841:
810:
610:Christiaan Huygens
596:built a clock for
330:. In astronomy, a
144:, the unperturbed
4942:
4941:
4907:Derived ESU units
4841:Derived EMU units
4718:
4717:
4585:
4584:
4463:astronomical unit
4240:
4239:
4050:Nuclear timescale
3732:Continuous signal
3471:
3470:
3381:
3380:
3356:Circadian rhythms
3174:Tenseâaspectâmood
3029:Temporal finitism
2906:
2905:
2882:Grandfather clock
2288:Draft resolutions
2100:(July 31, 1997).
1651:
1650:
1249:
1184:
1159:
1144:
1097:
985:
984:
839:
792:
724:Atomic definition
676:Tables of the Sun
203:pars minuta prima
96:) is the unit of
86:
85:
4977:
4745:
4738:
4731:
4722:
4644:<1 attosecond
4612:
4605:
4598:
4589:
4575:
4574:
4267:
4260:
4253:
4244:
3941:Dominical letter
3872:Equation of time
3835:Marine sandglass
3676:
3670:
3648:Terrestrial Time
3505:Time measurement
3498:
3491:
3484:
3475:
3461:
3460:
3451:
3450:
3368:Glottochronology
3208:
3124:Human experience
2984:B-theory of time
2582:
2526:
2519:
2512:
2503:
2434:
2432:
2430:
2428:
2419:. Archived from
2412:
2406:
2405:
2387:
2355:
2346:
2345:
2301:
2295:
2285:
2279:
2278:
2267:
2261:
2260:
2258:
2256:
2250:
2235:
2227:
2221:
2220:
2203:
2197:
2196:
2194:
2192:
2173:
2162:
2161:
2159:
2157:
2136:
2130:
2129:
2127:
2125:
2094:
2088:
2086:
2074:
2064:
2058:
2057:
2038:Landes, David S.
2034:
2023:
2022:
2000:
1994:
1993:
1991:
1989:
1968:
1962:
1961:
1959:
1957:
1937:
1931:
1930:
1919:
1906:
1905:
1903:
1901:
1887:
1881:
1880:
1862:
1830:
1824:
1823:
1821:
1819:
1813:
1798:
1790:
1773:
1769:
1763:
1732:
1726:
1707:
1701:
1691:
1670:Seconds pendulum
1660:Caesium standard
1328:
1268:
1260:
1258:
1257:
1252:
1250:
1248:
1247:
1238:
1231:
1230:
1220:
1212:
1211:
1195:
1193:
1192:
1187:
1185:
1183:
1175:
1174:
1173:
1161:
1160:
1157:
1150:
1145:
1143:
1139:
1138:
1128:
1123:
1110:
1109:
1108:
1099:
1098:
1095:
1088:
1083:
1082:
1065:Rydberg constant
1059:Rydberg constant
1054:
1050:
1042:
1034:
1032:
1031:
1026:
1011:
1000:
998:
905:
903:
902:
897:
895:
894:
890:
877:
876:
850:
848:
847:
842:
840:
832:
819:
817:
816:
811:
809:
808:
793:
785:
757:
735:hyperfine levels
711:
710:
706:
649:
648:
644:
598:William of Hesse
587:
551:
549:
548:
545:
542:
536:
532:
530:
529:
526:
523:
517:
513:
313:decimal prefixes
298:around the Sun.
262:
261:
257:
252:
251:
247:
211:
205:
182:ever so slightly
167:
166:
163:
160:
113:
112:
108:
40:
28:
4987:
4986:
4980:
4979:
4978:
4976:
4975:
4974:
4945:
4944:
4943:
4938:
4902:
4836:
4780:
4754:
4749:
4719:
4714:
4683:Positive powers
4678:
4637:Negative powers
4632:
4621:
4616:
4586:
4581:
4563:
4544:Metric prefixes
4527:
4449:
4331:
4324:
4276:
4271:
4241:
4236:
4173:
4064:
4031:
4005:
3886:
3786:
3737:Coordinate time
3709:Time in physics
3703:
3677:
3671:
3662:
3534:
3511:
3502:
3472:
3467:
3439:
3430:Time immemorial
3377:
3334:
3295:Coordinate time
3266:
3220:Geological time
3196:
3179:Time management
3142:Generation time
3126:
3118:
3063:
3045:
2965:
2924:
2902:
2790:
2708:
2625:
2618:
2574:
2566:
2535:
2530:
2443:
2438:
2437:
2426:
2424:
2414:
2413:
2409:
2357:
2356:
2349:
2303:
2302:
2298:
2286:
2282:
2269:
2268:
2264:
2254:
2252:
2248:
2244:. p. 112.
2233:
2229:
2228:
2224:
2205:
2204:
2200:
2190:
2188:
2175:
2174:
2165:
2155:
2153:
2138:
2137:
2133:
2123:
2121:
2114:
2096:
2095:
2091:
2083:
2066:
2065:
2061:
2054:
2036:
2035:
2026:
2019:
2002:
2001:
1997:
1987:
1985:
1970:
1969:
1965:
1955:
1953:
1939:
1938:
1934:
1921:
1920:
1909:
1899:
1897:
1889:
1888:
1884:
1832:
1831:
1827:
1817:
1815:
1811:
1807:. p. 130.
1796:
1792:
1791:
1787:
1782:
1777:
1776:
1770:
1766:
1733:
1729:
1708:
1704:
1692:
1688:
1683:
1656:
1297:
1291:
1279:
1266:
1239:
1222:
1221:
1203:
1198:
1197:
1176:
1165:
1152:
1151:
1130:
1111:
1100:
1090:
1089:
1074:
1069:
1068:
1061:
1052:
1048:
1045:optical lattice
1040:
1014:
1013:
1009:
996:
994:
990:
958:
878:
869:
864:
863:
826:
825:
797:
779:
778:
755:
749:for the world.
726:
709:31,556,925.9747
708:
704:
703:
662:
656:
646:
642:
641:
626:system of units
585:
561:
546:
543:
540:
539:
537:
534:
527:
524:
521:
520:
518:
515:
511:
507:
495:
489:
469:
463:
433:
427:
356:inverse seconds
344:
308:
280:
259:
255:
254:
249:
245:
244:
218:
198:
164:
161:
158:
156:
143:
110:
106:
105:
47:
24:
17:
16:SI unit of time
12:
11:
5:
4985:
4984:
4981:
4973:
4972:
4967:
4962:
4957:
4947:
4946:
4940:
4939:
4937:
4936:
4931:
4926:
4921:
4916:
4910:
4908:
4904:
4903:
4901:
4900:
4895:
4890:
4885:
4880:
4875:
4870:
4865:
4860:
4855:
4844:
4842:
4838:
4837:
4835:
4834:
4829:
4824:
4819:
4814:
4809:
4804:
4799:
4794:
4788:
4786:
4782:
4781:
4779:
4778:
4773:
4768:
4762:
4760:
4756:
4755:
4750:
4748:
4747:
4740:
4733:
4725:
4716:
4715:
4713:
4712:
4707:
4702:
4697:
4692:
4686:
4684:
4680:
4679:
4677:
4676:
4671:
4666:
4661:
4656:
4651:
4646:
4640:
4638:
4634:
4633:
4626:
4623:
4622:
4617:
4615:
4614:
4607:
4600:
4592:
4583:
4582:
4580:
4579:
4568:
4565:
4564:
4562:
4561:
4556:
4551:
4546:
4541:
4535:
4533:
4529:
4528:
4526:
4525:
4520:
4515:
4510:
4505:
4500:
4495:
4490:
4485:
4480:
4475:
4470:
4465:
4459:
4457:
4451:
4450:
4448:
4447:
4442:
4437:
4432:
4427:
4422:
4417:
4412:
4407:
4402:
4397:
4392:
4387:
4382:
4377:
4372:
4367:
4362:
4357:
4352:
4350:degree Celsius
4347:
4342:
4336:
4334:
4330:Derived units
4326:
4325:
4323:
4322:
4317:
4312:
4307:
4302:
4297:
4292:
4286:
4284:
4278:
4277:
4272:
4270:
4269:
4262:
4255:
4247:
4238:
4237:
4235:
4234:
4229:
4224:
4222:Time metrology
4219:
4214:
4209:
4204:
4199:
4198:
4197:
4187:
4181:
4179:
4178:Related topics
4175:
4174:
4172:
4171:
4166:
4161:
4156:
4151:
4146:
4141:
4136:
4131:
4126:
4121:
4116:
4111:
4106:
4101:
4096:
4091:
4086:
4081:
4075:
4073:
4066:
4065:
4063:
4062:
4057:
4052:
4047:
4041:
4039:
4033:
4032:
4030:
4029:
4024:
4019:
4013:
4011:
4007:
4006:
4004:
4003:
3998:
3993:
3988:
3983:
3978:
3973:
3968:
3963:
3958:
3953:
3948:
3943:
3938:
3933:
3928:
3923:
3917:
3912:
3907:
3902:
3896:
3894:
3888:
3887:
3885:
3884:
3879:
3874:
3869:
3867:Dialing scales
3864:
3859:
3854:
3853:
3852:
3842:
3837:
3832:
3827:
3822:
3817:
3812:
3807:
3802:
3796:
3794:
3788:
3787:
3785:
3784:
3779:
3774:
3769:
3764:
3759:
3754:
3749:
3744:
3739:
3734:
3729:
3724:
3719:
3713:
3711:
3705:
3704:
3702:
3701:
3699:Prime meridian
3696:
3691:
3689:Ephemeris time
3685:
3683:
3679:
3678:
3665:
3663:
3661:
3660:
3658:180th meridian
3655:
3650:
3645:
3640:
3635:
3630:
3625:
3620:
3615:
3610:
3605:
3600:
3595:
3590:
3585:
3580:
3575:
3570:
3565:
3560:
3555:
3554:
3553:
3542:
3540:
3536:
3535:
3533:
3532:
3527:
3522:
3516:
3513:
3512:
3503:
3501:
3500:
3493:
3486:
3478:
3469:
3468:
3466:
3465:
3455:
3444:
3441:
3440:
3438:
3437:
3432:
3427:
3422:
3415:
3410:
3405:
3400:
3395:
3389:
3387:
3383:
3382:
3379:
3378:
3376:
3375:
3373:Time geography
3370:
3365:
3363:Clock reaction
3360:
3359:
3358:
3348:
3342:
3340:
3336:
3335:
3333:
3332:
3327:
3322:
3317:
3312:
3307:
3302:
3297:
3292:
3287:
3282:
3276:
3274:
3268:
3267:
3265:
3264:
3259:
3254:
3253:
3252:
3247:
3242:
3237:
3232:
3227:
3216:
3214:
3205:
3198:
3197:
3195:
3194:
3181:
3176:
3171:
3166:
3165:
3164:
3162:time signature
3159:
3149:
3144:
3139:
3133:
3131:
3120:
3119:
3117:
3116:
3115:
3114:
3104:
3103:
3102:
3092:
3087:
3082:
3077:
3072:
3066:
3064:
3062:
3061:
3056:
3050:
3047:
3046:
3044:
3043:
3036:
3034:Temporal parts
3031:
3026:
3021:
3016:
3011:
3006:
3004:Eternal return
3001:
2996:
2991:
2989:Chronocentrism
2986:
2981:
2975:
2973:
2967:
2966:
2964:
2963:
2958:
2953:
2948:
2943:
2938:
2933:
2927:
2925:
2923:
2922:
2917:
2911:
2908:
2907:
2904:
2903:
2901:
2900:
2899:
2898:
2884:
2879:
2874:
2869:
2868:
2867:
2862:
2861:
2860:
2855:
2845:
2840:
2835:
2830:
2829:
2828:
2818:
2817:
2816:
2800:
2798:
2792:
2791:
2789:
2788:
2781:
2776:
2774:Hindu Panchang
2771:
2766:
2761:
2756:
2751:
2746:
2741:
2740:
2739:
2734:
2729:
2718:
2716:
2710:
2709:
2707:
2706:
2701:
2696:
2691:
2686:
2681:
2676:
2671:
2666:
2661:
2656:
2651:
2646:
2641:
2636:
2630:
2628:
2620:
2619:
2617:
2616:
2611:
2606:
2601:
2596:
2590:
2588:
2579:
2568:
2567:
2565:
2564:
2559:
2554:
2549:
2543:
2541:
2537:
2536:
2531:
2529:
2528:
2521:
2514:
2506:
2500:
2499:
2494:
2487:
2482:
2477:
2468:
2460:
2452:
2442:
2441:External links
2439:
2436:
2435:
2407:
2347:
2296:
2280:
2262:
2222:
2218:in Sept. 1952.
2198:
2177:"Leap Seconds"
2163:
2142:, ed. (1873).
2131:
2112:
2098:Selin, Helaine
2089:
2081:
2059:
2052:
2024:
2017:
1995:
1963:
1932:
1907:
1882:
1825:
1784:
1783:
1781:
1778:
1775:
1774:
1764:
1727:
1702:
1685:
1684:
1682:
1679:
1678:
1677:
1672:
1667:
1662:
1655:
1652:
1649:
1648:
1645:
1642:
1639:
1636:
1633:
1630:
1626:
1625:
1622:
1619:
1616:
1613:
1610:
1607:
1603:
1602:
1599:
1596:
1593:
1590:
1587:
1584:
1580:
1579:
1576:
1573:
1570:
1567:
1564:
1561:
1557:
1556:
1553:
1550:
1547:
1544:
1539:
1536:
1532:
1531:
1528:
1525:
1522:
1519:
1514:
1511:
1507:
1506:
1503:
1500:
1497:
1494:
1489:
1486:
1482:
1481:
1478:
1475:
1472:
1469:
1464:
1461:
1457:
1456:
1453:
1450:
1447:
1444:
1439:
1436:
1432:
1431:
1428:
1425:
1422:
1419:
1414:
1411:
1407:
1406:
1403:
1400:
1397:
1394:
1391:
1388:
1384:
1383:
1380:
1377:
1374:
1371:
1368:
1365:
1361:
1360:
1359:Equivalent to
1357:
1354:
1351:
1348:
1345:
1342:
1338:
1337:
1334:
1332:
1293:Main article:
1290:
1287:
1278:
1275:
1246:
1242:
1237:
1234:
1229:
1225:
1218:
1215:
1210:
1206:
1182:
1179:
1172:
1168:
1164:
1155:
1148:
1142:
1137:
1133:
1127:
1122:
1118:
1114:
1107:
1103:
1093:
1086:
1081:
1077:
1060:
1057:
1024:
1021:
1006:Optical clocks
989:
986:
983:
982:
980:SI Brochure 9
973:
956:
949:
933:
932:
926:
922:
917:
916:
910:
907:
893:
889:
885:
881:
875:
871:
859:
858:
852:
838:
835:
822:
807:
804:
800:
796:
791:
788:
773:
772:
769:
766:
762:
761:
754:
751:
725:
722:
681:ephemeris time
660:Ephemeris time
655:
652:
560:
557:
506:
503:
488:
485:
465:Main article:
462:
459:
455:universal time
429:Main article:
426:
423:
391:speed of light
343:
340:
307:
304:
279:
276:
241:shutter speeds
217:
214:
197:
194:
178:caesium clocks
141:
84:
83:
80:
76:
75:
70:
66:
65:
60:
54:
53:
49:
48:
41:
33:
32:
15:
13:
10:
9:
6:
4:
3:
2:
4983:
4982:
4971:
4970:Units of time
4968:
4966:
4965:SI base units
4963:
4961:
4958:
4956:
4953:
4952:
4950:
4935:
4932:
4930:
4927:
4925:
4922:
4920:
4917:
4915:
4912:
4911:
4909:
4905:
4899:
4896:
4894:
4891:
4889:
4886:
4884:
4881:
4879:
4876:
4874:
4871:
4869:
4866:
4864:
4861:
4859:
4856:
4853:
4849:
4846:
4845:
4843:
4839:
4833:
4830:
4828:
4825:
4823:
4820:
4818:
4815:
4813:
4810:
4808:
4805:
4803:
4800:
4798:
4795:
4793:
4790:
4789:
4787:
4783:
4777:
4774:
4772:
4769:
4767:
4764:
4763:
4761:
4757:
4753:
4746:
4741:
4739:
4734:
4732:
4727:
4726:
4723:
4711:
4708:
4706:
4703:
4701:
4698:
4696:
4693:
4691:
4688:
4687:
4685:
4681:
4675:
4672:
4670:
4667:
4665:
4662:
4660:
4657:
4655:
4652:
4650:
4647:
4645:
4642:
4641:
4639:
4635:
4630:
4624:
4620:
4613:
4608:
4606:
4601:
4599:
4594:
4593:
4590:
4578:
4570:
4569:
4566:
4560:
4557:
4555:
4552:
4550:
4547:
4545:
4542:
4540:
4537:
4536:
4534:
4530:
4524:
4521:
4519:
4516:
4514:
4511:
4509:
4506:
4504:
4501:
4499:
4496:
4494:
4491:
4489:
4486:
4484:
4483:degree of arc
4481:
4479:
4476:
4474:
4471:
4469:
4466:
4464:
4461:
4460:
4458:
4456:
4452:
4446:
4443:
4441:
4438:
4436:
4433:
4431:
4428:
4426:
4423:
4421:
4418:
4416:
4413:
4411:
4408:
4406:
4403:
4401:
4398:
4396:
4393:
4391:
4388:
4386:
4383:
4381:
4378:
4376:
4373:
4371:
4368:
4366:
4363:
4361:
4358:
4356:
4353:
4351:
4348:
4346:
4343:
4341:
4338:
4337:
4335:
4333:
4327:
4321:
4318:
4316:
4313:
4311:
4308:
4306:
4303:
4301:
4298:
4296:
4293:
4291:
4288:
4287:
4285:
4283:
4279:
4275:
4268:
4263:
4261:
4256:
4254:
4249:
4248:
4245:
4233:
4230:
4228:
4225:
4223:
4220:
4218:
4215:
4213:
4210:
4208:
4205:
4203:
4200:
4196:
4193:
4192:
4191:
4188:
4186:
4183:
4182:
4180:
4176:
4170:
4167:
4165:
4162:
4160:
4157:
4155:
4152:
4150:
4147:
4145:
4142:
4140:
4137:
4135:
4132:
4130:
4127:
4125:
4122:
4120:
4117:
4115:
4112:
4110:
4107:
4105:
4102:
4100:
4097:
4095:
4092:
4090:
4087:
4085:
4082:
4080:
4077:
4076:
4074:
4072:
4071:units of time
4067:
4061:
4060:Sidereal time
4058:
4056:
4053:
4051:
4048:
4046:
4045:Galactic year
4043:
4042:
4040:
4038:
4034:
4028:
4025:
4023:
4020:
4018:
4015:
4014:
4012:
4008:
4002:
4001:Weekday names
3999:
3997:
3994:
3992:
3991:Tropical year
3989:
3987:
3984:
3982:
3979:
3977:
3974:
3972:
3969:
3967:
3964:
3962:
3959:
3957:
3956:Intercalation
3954:
3952:
3949:
3947:
3944:
3942:
3939:
3937:
3934:
3932:
3929:
3927:
3924:
3922:(lunar Hijri)
3921:
3918:
3916:
3913:
3911:
3908:
3906:
3903:
3901:
3898:
3897:
3895:
3893:
3889:
3883:
3880:
3878:
3875:
3873:
3870:
3868:
3865:
3863:
3860:
3858:
3855:
3851:
3848:
3847:
3846:
3843:
3841:
3838:
3836:
3833:
3831:
3828:
3826:
3823:
3821:
3818:
3816:
3813:
3811:
3808:
3806:
3803:
3801:
3798:
3797:
3795:
3793:
3789:
3783:
3780:
3778:
3775:
3773:
3770:
3768:
3765:
3763:
3762:Time dilation
3760:
3758:
3755:
3753:
3750:
3748:
3745:
3743:
3740:
3738:
3735:
3733:
3730:
3728:
3725:
3723:
3720:
3718:
3715:
3714:
3712:
3710:
3706:
3700:
3697:
3695:
3692:
3690:
3687:
3686:
3684:
3680:
3675:
3669:
3659:
3656:
3654:
3651:
3649:
3646:
3644:
3641:
3639:
3636:
3634:
3631:
3629:
3626:
3624:
3621:
3619:
3616:
3614:
3611:
3609:
3606:
3604:
3601:
3599:
3598:24-hour clock
3596:
3594:
3593:12-hour clock
3591:
3589:
3586:
3584:
3581:
3579:
3576:
3574:
3571:
3569:
3566:
3564:
3561:
3559:
3556:
3552:
3549:
3548:
3547:
3544:
3543:
3541:
3537:
3531:
3528:
3526:
3523:
3521:
3518:
3517:
3514:
3510:
3506:
3499:
3494:
3492:
3487:
3485:
3480:
3479:
3476:
3464:
3456:
3454:
3446:
3445:
3442:
3436:
3433:
3431:
3428:
3426:
3423:
3421:
3420:
3416:
3414:
3411:
3409:
3406:
3404:
3401:
3399:
3396:
3394:
3391:
3390:
3388:
3384:
3374:
3371:
3369:
3366:
3364:
3361:
3357:
3354:
3353:
3352:
3351:Chronobiology
3349:
3347:
3344:
3343:
3341:
3337:
3331:
3328:
3326:
3323:
3321:
3318:
3316:
3313:
3311:
3308:
3306:
3303:
3301:
3298:
3296:
3293:
3291:
3288:
3286:
3285:Arrow of time
3283:
3281:
3278:
3277:
3275:
3273:
3269:
3263:
3260:
3258:
3257:Geochronology
3255:
3251:
3248:
3246:
3243:
3241:
3238:
3236:
3233:
3231:
3228:
3226:
3223:
3222:
3221:
3218:
3217:
3215:
3213:
3209:
3206:
3204:
3199:
3193:
3189:
3185:
3182:
3180:
3177:
3175:
3172:
3170:
3167:
3163:
3160:
3158:
3155:
3154:
3153:
3150:
3148:
3145:
3143:
3140:
3138:
3135:
3134:
3132:
3130:
3125:
3121:
3113:
3110:
3109:
3108:
3107:Wheel of time
3105:
3101:
3098:
3097:
3096:
3093:
3091:
3088:
3086:
3083:
3081:
3078:
3076:
3073:
3071:
3068:
3067:
3065:
3060:
3057:
3055:
3052:
3051:
3048:
3042:
3041:
3037:
3035:
3032:
3030:
3027:
3025:
3022:
3020:
3017:
3015:
3012:
3010:
3007:
3005:
3002:
3000:
2997:
2995:
2992:
2990:
2987:
2985:
2982:
2980:
2977:
2976:
2974:
2972:
2968:
2962:
2959:
2957:
2954:
2952:
2951:Periodization
2949:
2947:
2944:
2942:
2939:
2937:
2934:
2932:
2929:
2928:
2926:
2921:
2918:
2916:
2913:
2912:
2909:
2897:
2896:
2892:
2891:
2890:
2889:
2885:
2883:
2880:
2878:
2877:Digital clock
2875:
2873:
2870:
2866:
2863:
2859:
2856:
2854:
2851:
2850:
2849:
2846:
2844:
2841:
2839:
2836:
2834:
2831:
2827:
2824:
2823:
2822:
2819:
2815:
2812:
2811:
2810:
2807:
2806:
2805:
2802:
2801:
2799:
2797:
2793:
2787:
2786:
2782:
2780:
2777:
2775:
2772:
2770:
2767:
2765:
2762:
2760:
2757:
2755:
2752:
2750:
2747:
2745:
2742:
2738:
2735:
2733:
2730:
2728:
2725:
2724:
2723:
2720:
2719:
2717:
2715:
2711:
2705:
2702:
2700:
2697:
2695:
2692:
2690:
2687:
2685:
2682:
2680:
2677:
2675:
2672:
2670:
2667:
2665:
2662:
2660:
2657:
2655:
2654:Relative hour
2652:
2650:
2649:24-hour clock
2647:
2645:
2644:12-hour clock
2642:
2640:
2637:
2635:
2632:
2631:
2629:
2627:
2621:
2615:
2612:
2610:
2607:
2605:
2602:
2600:
2597:
2595:
2592:
2591:
2589:
2587:
2583:
2580:
2578:
2573:
2569:
2563:
2560:
2558:
2555:
2553:
2550:
2548:
2545:
2544:
2542:
2538:
2534:
2527:
2522:
2520:
2515:
2513:
2508:
2507:
2504:
2498:
2495:
2493:
2492:
2488:
2486:
2483:
2481:
2478:
2476:
2474:
2469:
2467:
2466:
2461:
2459:
2457:
2453:
2451:
2450:
2445:
2444:
2440:
2422:
2418:
2411:
2408:
2403:
2399:
2395:
2391:
2386:
2381:
2377:
2373:
2369:
2365:
2361:
2354:
2352:
2348:
2343:
2339:
2335:
2331:
2327:
2323:
2319:
2315:
2311:
2307:
2300:
2297:
2293:
2289:
2284:
2281:
2276:
2272:
2266:
2263:
2247:
2243:
2239:
2232:
2226:
2223:
2219:
2217:
2212:, p. 9,
2211:
2210:
2202:
2199:
2186:
2182:
2178:
2172:
2170:
2168:
2164:
2151:
2147:
2146:
2141:
2135:
2132:
2119:
2115:
2113:0-7923-4066-3
2109:
2105:
2104:
2099:
2093:
2090:
2084:
2082:0-8037-4475-7
2078:
2073:
2072:
2063:
2060:
2055:
2053:0-674-76802-7
2049:
2045:
2044:
2039:
2033:
2031:
2029:
2025:
2020:
2018:1-85506-856-7
2014:
2010:
2006:
1999:
1996:
1983:
1979:
1978:
1973:
1967:
1964:
1951:
1947:
1943:
1936:
1933:
1928:
1924:
1918:
1916:
1914:
1912:
1908:
1900:September 20,
1896:
1892:
1886:
1883:
1878:
1874:
1870:
1866:
1861:
1856:
1852:
1848:
1844:
1840:
1836:
1829:
1826:
1810:
1806:
1802:
1795:
1789:
1786:
1779:
1768:
1765:
1761:
1757:
1753:
1749:
1745:
1741:
1737:
1731:
1728:
1724:
1720:
1716:
1712:
1709:In 1000, the
1706:
1703:
1699:
1695:
1690:
1687:
1680:
1676:
1675:Time standard
1673:
1671:
1668:
1666:
1663:
1661:
1658:
1657:
1653:
1646:
1644:quettasecond
1643:
1640:
1637:
1635:quectosecond
1634:
1631:
1628:
1627:
1623:
1620:
1617:
1614:
1611:
1608:
1605:
1604:
1600:
1597:
1594:
1591:
1588:
1585:
1582:
1581:
1577:
1574:
1571:
1568:
1565:
1562:
1559:
1558:
1554:
1551:
1548:
1545:
1543:
1540:
1537:
1534:
1533:
1529:
1526:
1523:
1520:
1518:
1515:
1512:
1509:
1508:
1505:31,700 years
1504:
1501:
1498:
1495:
1493:
1490:
1487:
1484:
1483:
1479:
1476:
1473:
1470:
1468:
1465:
1462:
1459:
1458:
1454:
1451:
1448:
1445:
1443:
1440:
1437:
1434:
1433:
1429:
1426:
1423:
1420:
1418:
1415:
1412:
1409:
1408:
1404:
1401:
1398:
1395:
1392:
1389:
1386:
1385:
1381:
1378:
1375:
1372:
1369:
1366:
1363:
1362:
1358:
1355:
1352:
1349:
1346:
1343:
1340:
1339:
1331:Submultiples
1329:
1323:
1321:
1317:
1313:
1309:
1305:
1301:
1296:
1288:
1286:
1285:
1284:fiber-optics.
1276:
1274:
1272:
1267:121.5 nm
1262:
1244:
1240:
1235:
1232:
1223:
1216:
1213:
1208:
1204:
1180:
1177:
1170:
1166:
1162:
1153:
1146:
1140:
1135:
1131:
1125:
1120:
1116:
1112:
1105:
1101:
1091:
1084:
1075:
1066:
1058:
1056:
1046:
1038:
1022:
1007:
1003:
987:
981:
977:
974:
972:
968:
964:
960:
955:
950:
948:
944:
940:
935:
934:
931:
927:
923:
919:
918:
915:
911:
908:
891:
887:
883:
879:
873:
870:
861:
860:
857:
853:
837:31556925.9747
836:
833:
823:
821:
805:
802:
798:
794:
789:
786:
775:
774:
770:
767:
764:
763:
758:
752:
750:
748:
747:time standard
743:
740:
736:
732:
723:
721:
719:
715:
701:
696:
694:
693:tropical year
690:
686:
685:sidereal year
682:
678:
677:
670:
668:
661:
653:
651:
639:
635:
631:
627:
623:
618:
616:
615:John Harrison
611:
606:
603:
599:
595:
591:
583:
577:
575:
572:displayed by
571:
570:apparent time
567:
558:
556:
553:
504:
502:
500:
494:
486:
484:
482:
478:
474:
468:
460:
458:
456:
451:
449:
445:
440:
438:
432:
431:Time standard
424:
422:
420:
416:
412:
408:
404:
400:
396:
392:
388:
384:
383:SI base units
379:
377:
373:
369:
365:
361:
357:
353:
349:
341:
339:
335:
333:
329:
325:
321:
316:
314:
305:
303:
299:
297:
293:
292:apparent time
289:
285:
277:
275:
273:
272:atomic clocks
268:
264:
242:
237:
233:
229:
226:
222:
221:Analog clocks
215:
213:
210:
204:
195:
193:
191:
187:
183:
179:
173:
171:
154:
150:
147:
140:
134:
132:
127:
125:
122:, then to 60
121:
117:
103:
99:
95:
91:
81:
77:
74:
71:
67:
64:
61:
59:
55:
50:
45:
39:
34:
29:
26:
22:
4775:
4689:
4488:electronvolt
4319:
4207:Decimal time
4098:
3936:Astronomical
3815:Complication
3810:Atomic clock
3425:Time capsule
3419:Tempus fugit
3417:
3339:Other fields
3038:
3019:Perdurantism
2941:Calendar era
2893:
2886:
2872:Cuckoo clock
2809:astronomical
2783:
2609:Unit of time
2540:Key concepts
2490:
2472:
2464:
2455:
2448:
2427:February 18,
2425:. Retrieved
2421:the original
2410:
2367:
2363:
2309:
2305:
2299:
2283:
2274:
2265:
2253:. Retrieved
2237:
2225:
2213:
2208:
2201:
2191:November 22,
2189:. Retrieved
2156:February 23,
2154:. Retrieved
2144:
2134:
2124:February 23,
2122:. Retrieved
2102:
2092:
2070:
2062:
2041:
2004:
1998:
1988:February 23,
1986:. Retrieved
1976:
1966:
1954:. Retrieved
1945:
1935:
1926:
1898:. Retrieved
1894:
1885:
1842:
1838:
1828:
1816:. Retrieved
1800:
1788:
1767:
1759:
1755:
1751:
1747:
1743:
1730:
1718:
1705:
1689:
1621:ronnasecond
1612:rontosecond
1598:yottasecond
1589:yoctosecond
1575:zettasecond
1566:zeptosecond
1402:hectosecond
1393:centisecond
1320:Julian years
1298:
1289:SI multiples
1280:
1277:Requirements
1263:
1062:
1004:
991:
979:
975:
969:
965:
961:
953:
951:
945:
941:
938:
929:
913:
855:
777:
771:Information
744:
727:
697:
675:
671:
667:Metrologists
663:
619:
607:
578:
569:
565:
562:
554:
508:
496:
470:
452:
448:leap seconds
441:
434:
380:
364:acceleration
350:measured in
345:
336:
328:leap seconds
317:
309:
300:
291:
283:
281:
265:
235:
230:
219:
199:
175:
155:atom, to be
146:ground-state
138:
136:
128:
93:
89:
87:
69:Unit of
25:
4919:statcoulomb
4674:millisecond
4669:microsecond
4654:femtosecond
4217:System time
4212:Metric time
3931:Solar Hijri
3857:Water clock
3840:Radio clock
3772:Time domain
3752:Proper time
3638:Leap second
3520:Chronometry
3435:Time travel
3413:System time
3320:Time domain
3305:Proper time
3129:use of time
3100:Father Time
3080:Immortality
3070:Ages of Man
2999:Endurantism
2956:Regnal year
2936:Big History
2865:water-based
2764:Solar Hijri
2674:Hexadecimal
2624:Measurement
2586:Chronometry
2572:Measurement
2290:of the 27.
1956:January 26,
1801:SI Brochure
1736:Roger Bacon
1527:petasecond
1517:femtosecond
1502:terasecond
1480:31.7 years
1477:gigasecond
1452:megasecond
1442:microsecond
1427:kilosecond
1417:millisecond
1382:10 seconds
1379:decasecond
1370:decisecond
1300:SI prefixes
787:12960276813
739:caesium-133
602:Tycho Brahe
590:Taqi al-Din
332:Julian year
267:Sexagesimal
232:SI prefixes
186:leap second
153:caesium 133
58:Unit system
4949:Categories
4914:statampere
4766:centimetre
4759:Base units
4705:gigasecond
4700:megasecond
4695:kilosecond
4664:nanosecond
4659:picosecond
4649:attosecond
4282:Base units
4232:Timekeeper
4185:Chronology
4169:Millennium
4055:Precession
3961:Julian day
3782:T-symmetry
3643:Solar time
3613:Civil time
3137:Chronemics
3112:Kalachakra
3024:Presentism
3009:Eternalism
2915:Chronology
2853:mechanical
2804:Main types
2722:Main types
1780:References
1740:full moons
1694:Civil time
1552:exasecond
1542:attosecond
1492:picosecond
1467:nanosecond
1353:SI symbol
1344:SI symbol
1336:Multiples
1271:Lamb shift
1010:10 Hz
914:CIPM 1967
854:1956 CIPM
674:Newcomb's
658:See also:
634:CGS system
594:Jost BĂźrgi
491:See also:
320:leap years
253:second or
190:civil time
44:escapement
4858:abcoulomb
4752:CGS units
4425:steradian
4340:becquerel
4129:Fortnight
3976:Lunisolar
3966:Leap year
3900:Gregorian
3850:stopwatch
3825:Hourglass
3805:Astrarium
3722:Spacetime
3653:Time zone
3530:Metrology
3509:standards
3393:Leap year
3310:Spacetime
3184:Yesterday
3085:Dreamtime
3059:Mythology
2946:Deep time
2858:stopwatch
2833:hourglass
2814:astrarium
2744:Gregorian
2737:Lunisolar
2714:Calendars
2704:Time zone
2577:standards
1974:(1879) .
1972:Al-Biruni
1723:new moons
1715:al-Biruni
1228:∞
1217:−
1214:≈
1167:α
1117:ε
1080:∞
1039:is about
1020:Δ
803:−
795:×
790:408986496
720:in 1960.
714:January 0
620:In 1832,
566:mean time
473:strontium
419:steradian
368:becquerel
348:frequency
324:Gregorian
284:mean time
196:Etymology
149:hyperfine
92:(symbol:
4934:statvolt
4848:abampere
4577:Category
4532:See also
4305:kilogram
4274:SI units
4190:Duration
4164:Saeculum
4144:Olympiad
3986:Solstice
3915:Holocene
3892:Calendar
3792:Horology
3583:ISO 8601
3578:ISO 31-1
3453:Category
3201:Time in
3192:Tomorrow
3054:Religion
2994:Duration
2961:Timeline
2895:Timeline
2694:Sidereal
2562:Eternity
2394:21930568
2334:21930568
2246:Archived
2185:Archived
2150:Archived
2118:Archived
2040:(1983).
1982:Archived
1950:Archived
1946:TheVerge
1869:21930568
1809:Archived
1713:scholar
1654:See also
1037:Q-factor
937:fields.
574:sundials
395:kilogram
374:such as
263:second.
4929:statohm
4924:statmho
4898:oersted
4893:maxwell
4888:gilbert
4863:abhenry
4493:hectare
4478:decibel
4420:sievert
4415:siemens
4345:coulomb
4295:candela
4159:Century
4149:Lustrum
4079:Instant
3951:Equinox
3920:Islamic
3862:Sundial
3727:Chronon
3463:Commons
3386:Related
3300:Instant
3290:Chronon
3272:Physics
3212:Geology
3203:science
3075:Destiny
2920:History
2888:History
2843:sundial
2826:quantum
2769:Chinese
2759:Islamic
2669:Decimal
2664:Chinese
2626:systems
2552:Present
2402:6896025
2372:Bibcode
2342:6896025
2314:Bibcode
2255:May 23,
1877:6896025
1847:Bibcode
1818:May 23,
1752:secunda
1711:Persian
1308:minutes
1055:atoms.
731:periods
707:⁄
645:⁄
582:Orpheus
550:
538:
531:
519:
499:caesium
407:candela
358:or s),
288:sundial
258:⁄
248:⁄
225:watches
124:minutes
109:⁄
100:in the
4878:abvolt
4822:kayser
4812:kelvin
4776:second
4690:second
4631:of ten
4629:powers
4508:minute
4468:dalton
4410:radian
4405:pascal
4395:newton
4320:second
4300:kelvin
4290:ampere
4154:Decade
4109:Moment
4104:Minute
4099:Second
4069:Other
3926:Julian
3905:Hebrew
3551:offset
3403:Moment
3398:Memory
3250:period
2838:marine
2821:atomic
2796:Clocks
2754:Hebrew
2749:Julian
2684:Metric
2557:Future
2471:NIST:
2400:
2392:
2340:
2332:
2110:
2079:
2050:
2015:
1875:
1867:
1772:marks.
1760:quarta
1758:, and
1756:tertia
1748:minuta
1719:second
1350:Value
1341:Value
647:86,400
628:. The
535:
516:
512:
510:second
415:radian
405:, and
403:kelvin
399:ampere
236:second
90:second
79:Symbol
31:second
4883:gauss
4873:abohm
4868:abmho
4832:stilb
4817:poise
4792:barye
4523:tonne
4518:neper
4503:litre
4445:weber
4430:tesla
4385:lumen
4380:katal
4375:joule
4370:hertz
4365:henry
4355:farad
4310:metre
4195:music
4134:Month
4094:Jiffy
4089:Shake
4084:Flick
3981:Solar
3971:Lunar
3946:Epact
3910:Hindu
3845:Watch
3800:Clock
3408:Space
3240:epoch
3230:chron
3188:Today
3157:tempo
3152:Music
3014:Event
2848:watch
2732:Lunar
2727:Solar
2699:Solar
2689:Roman
2679:Hindu
2398:S2CID
2338:S2CID
2249:(PDF)
2234:(PDF)
1873:S2CID
1812:(PDF)
1797:(PDF)
1744:horae
1681:Notes
1638:10 s
1629:10 s
1615:10 s
1606:10 s
1592:10 s
1583:10 s
1569:10 s
1560:10 s
1546:10 s
1535:10 s
1521:10 s
1510:10 s
1496:10 s
1485:10 s
1471:10 s
1460:10 s
1446:10 s
1435:10 s
1421:10 s
1410:10 s
1396:10 s
1387:10 s
1373:10 s
1364:10 s
1356:Name
1347:Name
1312:hours
1047:with
753:Table
700:epoch
622:Gauss
586:1570.
547:60Ă60
528:60Ă60
387:meter
360:speed
352:hertz
296:orbit
120:hours
114:of a
111:86400
4852:biot
4827:phot
4797:dyne
4771:gram
4498:hour
4440:watt
4435:volt
4360:gray
4315:mole
4139:Year
4124:Week
4114:Hour
3568:DUT1
3507:and
3127:and
3090:KÄla
2785:List
2779:Maya
2575:and
2547:Past
2533:Time
2429:2007
2390:PMID
2330:PMID
2257:2019
2242:BIPM
2193:2015
2158:2016
2126:2016
2108:ISBN
2077:ISBN
2048:ISBN
2013:ISBN
1990:2016
1958:2018
1902:2021
1865:PMID
1820:2019
1805:BIPM
1376:das
1316:days
541:hour
417:and
411:mole
376:jerk
260:1000
223:and
216:Uses
184:, a
98:time
88:The
73:time
4807:gal
4802:erg
4627:by
4473:day
4400:ohm
4390:lux
4119:Day
3245:era
3235:eon
3225:age
2604:TAI
2594:UTC
2380:doi
2368:369
2322:doi
2310:369
1855:doi
1843:369
1641:Qs
1632:qs
1618:Rs
1609:rs
1595:Ys
1586:ys
1572:Zs
1563:zs
1549:Es
1538:as
1524:Ps
1513:fs
1499:Ts
1488:ps
1474:Gs
1463:ns
1449:Ms
1438:Îźs
1424:ks
1413:ms
1399:hs
1390:cs
1367:ds
689:IAU
638:MKS
522:day
477:THz
165:770
162:631
159:192
116:day
4951::
3563:ÎT
3558:UT
3190:â
3186:â
2599:UT
2396:.
2388:.
2378:.
2366:.
2362:.
2350:^
2336:.
2328:.
2320:.
2308:.
2240:.
2236:.
2183:.
2166:^
2116:.
2027:^
1948:.
1944:.
1910:^
1893:.
1871:.
1863:.
1853:.
1841:.
1837:.
1803:.
1799:.
1754:,
1750:,
1746:,
1322:.
1314:,
1310:,
1306::
1261:.
1053:10
1049:10
1041:10
999:10
957:Cs
799:10
483:.
401:,
397:,
250:30
170:Hz
142:Cs
63:SI
4854:)
4850:(
4744:e
4737:t
4730:v
4611:e
4604:t
4597:v
4266:e
4259:t
4252:v
3497:e
3490:t
3483:v
2525:e
2518:t
2511:v
2431:.
2404:.
2382::
2374::
2344:.
2324::
2316::
2259:.
2195:.
2160:.
2128:.
2085:.
2056:.
2021:.
1992:.
1960:.
1904:.
1879:.
1857::
1849::
1822:.
1245:2
1241:n
1236:h
1233:c
1224:R
1209:n
1205:E
1181:h
1178:2
1171:2
1163:c
1158:e
1154:m
1147:=
1141:c
1136:3
1132:h
1126:2
1121:0
1113:8
1106:4
1102:e
1096:e
1092:m
1085:=
1076:R
1051:â
1023:f
997:Ă
995:5
954:ν
892:2
888:/
884:1
880:S
874:2
834:1
806:9
705:1
643:1
544:/
525:/
514:=
354:(
256:1
246:1
157:9
139:ν
107:1
94:s
82:s
23:.
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
