2733:
643:
compensations, for refraction, aberration, precession, nutation and proper motion). It is well known that observations of the Sun pose substantial obstacles to the achievement of accuracy in measurement. In former times, before the distribution of accurate time signals, it was part of the routine work at any observatory to observe the sidereal times of meridian transit of selected 'clock stars' (of well-known position and movement), and to use these to correct observatory clocks running local mean sidereal time; but nowadays local sidereal time is usually generated by computer, based on time signals.
767:(TDT), which maintained continuity with it. TDT is a uniform atomic time scale, whose unit is the SI second. TDT is tied in its rate to the SI second, as is International Atomic Time (TAI), but because TAI was somewhat arbitrarily defined at its inception in 1958 to be initially equal to a refined version of UT, TDT was offset from TAI, by a constant 32.184 seconds. The offset provided a continuity from Ephemeris Time to TDT. TDT has since been redefined as
2727:
2508:
2518:
778:(TDB) was officially recommended to replace ET. TDB is similar to TDT but includes relativistic corrections that move the origin to the barycenter, hence it is a dynamical time at the barycenter. TDB differs from TT only in periodic terms. The difference is at most 2 milliseconds. Deficiencies were found in the definition of TDB (though not affecting T
679:. GMT either by that name or as 'mean time at Greenwich' used to be an international time standard, but is no longer so; it was initially renamed in 1928 as Universal Time (UT) (partly as a result of ambiguities arising from the changed practice of starting the astronomical day at midnight instead of at noon, adopted as from 1 January 1925).
642:
in the sky. For accurate astronomical work on land, it was usual to observe sidereal time rather than solar time to measure mean solar time, because the observations of 'fixed' stars could be measured and reduced more accurately than observations of the Sun (in spite of the need to make various small
347:
is a count of days elapsed since
Greenwich mean noon on 1 January 4713 B.C., Julian proleptic calendar. The Julian Date is the Julian day number followed by the fraction of the day elapsed since the preceding noon. Conveniently for astronomers, this avoids the date skip during an observation night.
34:
Historically, time standards were often based on the Earth's rotational period. From the late 18 century to the 19th century it was assumed that the Earth's daily rotational rate was constant. Astronomical observations of several kinds, including eclipse records, studied in the 19th century, raised
23:
is a specification for measuring time: either the rate at which time passes or points in time or both. In modern times, several time specifications have been officially recognized as standards, where formerly they were matters of custom and practice. An example of a kind of time standard can be a
370:
Conversions between atomic time systems (TAI, GPST, and UTC) are for the most part exact. However, GPS time is a measured value as opposed to a computed "paper" scale. As such it may differ from UTC(USNO) by a few hundred nanoseconds, which in turn may differ from official UTC by as much as 26
721:(ET) and its successor time scales described below have all been intended for astronomical use, e.g. in planetary motion calculations, with aims including uniformity, in particular, freedom from irregularities of Earth rotation. Some of these standards are examples of
348:
Modified Julian day (MJD) is defined as MJD = JD - 2400000.5. An MJD day thus begins at midnight, civil date. Julian dates can be expressed in UT1, TAI, TT, etc. and so for precise applications the timescale should be specified, e.g. MJD 49135.3824 TAI.
619:
is time by the stars. A sidereal rotation is the time it takes the Earth to make one revolution with rotation to the stars, approximately 23 hours 56 minutes 4 seconds. A mean solar day is about 3 minutes 56 seconds longer than a mean sidereal day, or
289:
at 0° longitude. At high precision, Earth's rotation is irregular and is determined from the positions of distant quasars using long baseline interferometry, laser ranging of the Moon and artificial satellites, as well as GPS satellite orbits.
609:, the apparent solar day varies a few dozen seconds above or below the mean value of 24 hours. As the variation accumulates over a few weeks, there are differences as large as 16 minutes between apparent solar time and mean solar time (see
745:; its length has been closely duplicated, to within 1 part in 10, in the size of the current SI second referred to atomic time. This Ephemeris Time standard was non-relativistic and did not fulfil growing needs for relativistic
1401:(1988) 'Comparisons of ET(Solar), ET(Lunar), UT and TDT', in (eds.) A K Babcock & G A Wilkins, 'The Earth's Rotation and Reference Frames for Geodesy and Geophysics', IAU Symposia #128 (1988), at pp 413-418.
89:
duration as a quantity characterizing a time interval. As a quantity, it has a value, such as a number of minutes, or may be described in terms of the quantities (such as times and dates) of its beginning and
296:(UTC) is an atomic time scale designed to approximate UT1. UTC differs from TAI by an integral number of seconds. UTC is kept within 0.9 second of UT1 by the introduction of one-second steps to UTC, the "
1217:
GPS time is automatically steered to UTC(USNO) on a daily basis to keep system time within one microsecond of UTC(USNO), but during the last several years has been within a few hundred nanoseconds.
576:
and TDB differs from TT in small, mostly periodic terms. Neglecting these terms (on the order of 2 milliseconds for several millennia around the present epoch), TCB is related to TT by: TCB − TT =
737:
based on the orbital motion of the Earth around the Sun, from which the ephemeris second was derived as a defined fraction of the tropical year. This ephemeris second was the standard for the
2631:
605:) and the next. A solar day is approximately 24 hours of mean time. Because the Earth's orbit around the Sun is elliptical, and because of the obliquity of the Earth's axis relative to the
2554:
653:, which compensated for two known irregularities in the length of the day, caused by the ellipticity of the Earth's orbit and the obliquity of the Earth's equator and polar axis to the
56:
Various types of second and day are used as the basic time interval for most time scales. Other intervals of time (minutes, hours, and years) are usually defined in terms of these two.
315:(GPST) to UTC. It was defined with a constant offset from TAI: GPST = TAI - 19 s. The GPS time standard is maintained independently but regularly synchronized with or from, UTC time.
133:
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 caesium atomic clock.
801:
and TDT/TT; and the same is true, to a lesser extent, of TCG. The ephemerides of Sun, Moon and planets in current widespread and official use continue to be those calculated at the
749:
scales. It was in use for the official almanacs and planetary ephemerides from 1960 to 1983, and was replaced in official almanacs for 1984 and after, by numerically integrated
691:(UTC) (an atomic-based time scale which is always kept within 0.9 second of UT1) is in common actual use in the UK, and the name GMT is often used to refer to it. (See articles
53:
has led to the replacement of older and purely astronomical time standards, for most practical purposes, by newer time standards based wholly or partly on atomic time.
750:
371:
nanoseconds. Conversions for UT1 and TT rely on published difference tables which as of 2022 are specified to 10 microseconds and 0.1 nanoseconds respectively.
2547:
248:
77:
as a quantity characterising an instant. As a quantity, it has a value which may be expressed in a variety of ways, for example "2014-04-26T09:42:36,75" in
613:). However, these variations cancel out over a year. There are also other perturbations such as Earth's wobble, but these are less than a second per year.
649:
was a time standard used especially at sea for navigational purposes, calculated by observing apparent solar time and then adding to it a correction, the
3323:
39:
rotates is gradually slowing and also shows small-scale irregularities, and this was confirmed in the early twentieth century. Time standards based on
797:, a specific fixed linear transformation of TCB. As defined, TCB (as observed from the Earth's surface) is of divergent rate relative to all of ET, T
3085:
2540:
2117:
1953:
1582:
986:
24:
time scale, specifying a method for measuring divisions of time. A standard for civil time can specify both time intervals and time-of-day.
3054:
1239:
1044:
1128:
2805:
1503:
672:
222:). The SI second is the basis of all atomic timescales, e.g. coordinated universal time, GPS time, International Atomic Time, etc.
730:
337:
meridian. Alternatively the difference is not really fixed, but it changes twice a year by a round amount, usually one hour, see
3819:
3814:
2067:
1722:
1531:
1003:
165:
also knew that Earth's orbit around the Sun (a year) was much more stable than Earth's rotation. This led to the definition of
255:
around the world, each corrected for environmental and relativistic effects (both gravitational and because of speed, like in
237:
having its spatial origin at the center of Earth's mass. TCG is a theoretical ideal, and any particular realization will have
31:
to count periods of some period changes, which may be either the changes of a natural phenomenon or of an artificial machine.
3316:
2878:
1946:
1176:
601:
or true solar time is based on the solar day, which is the period between one solar noon (passage of the real Sun across the
49:
standard based on the Earth's orbital period and in practice on the motion of the Moon. The invention in 1955 of the caesium
1095:
3799:
3059:
188:
2029:
161:
In the late 1940s, quartz crystal oscillator clocks could measure time more accurately than the rotation of the Earth.
3014:
2994:
2940:
2825:
2661:
2320:
1554:
1147:
1069:
953:
783:
668:
351:
1539:
1007:
2232:
1470:
Fig. 1 at p.835, a graph giving an overview of the rate differences and offsets between various standard time scales
3332:
2681:
2666:
2604:
2583:
1672:
1652:
787:
775:
764:
700:
688:
573:
293:
260:
230:
86:
time interval as an object – part of the time axis limited by two instants. Being an object, it has no value;
136:
In early history, clocks were not accurate enough to track seconds. After the invention of mechanical clocks, the
3309:
2835:
2646:
2383:
2112:
1662:
1575:
802:
304:
244:
2082:
3835:
3510:
3436:
3095:
2873:
2775:
2691:
2686:
2338:
1989:
1264:
333:, usually UTC. The offset is chosen such that a new day starts approximately while the Sun is crossing the
114:
and its life. Chronology, periodization, and interpretation of the past are together known as the study of
1692:
3248:
2153:
2098:
2052:
2037:
1682:
827:
267:(TT), a theoretical timescale that is a rescaling of TCG such that the time rate approximately matches
1555:
Why is a minute divided into 60 seconds, an hour into 60 minutes, yet there are only 24 hours in a day
915:
IEC 60050-113:2011, item 113-01-012: "mark attributed to an instant by means of a specified time scale
3861:
3856:
3350:
3075:
2989:
2815:
2676:
2404:
2373:
1822:
1717:
1568:
1427:
1365:
734:
722:
602:
530:
338:
282:
256:
687:
but is still the legal time in the UK in winter (and as adjusted by one hour for summer time). But
3804:
3791:
3285:
3080:
2935:
2800:
2752:
2621:
2278:
1737:
1697:
872:
692:
664:
598:
207:
141:
107:
40:
3809:
3734:
3626:
3514:
3432:
3370:
3260:
3034:
2958:
2888:
2227:
2205:
2072:
1896:
1867:
1802:
1795:
1411:
1201:
842:
1521:
1461:
194:
Most recently, atomic clocks have been developed that offer improved accuracy. Since 1967, the
3108:
2973:
2790:
2308:
2187:
2087:
1940:
1843:
1747:
1499:
1443:
1398:
1381:
1349:
982:
852:
837:
238:
3499:
2521:
1295:
3253:
2999:
2978:
2930:
2893:
2706:
2426:
2414:
2242:
2210:
2042:
1911:
1827:
1817:
1732:
1435:
1373:
1232:
768:
650:
610:
264:
2984:
2963:
2795:
2767:
2488:
2353:
2330:
2298:
2250:
2237:
2200:
2182:
1812:
1807:
1543:
1415:
1132:
1029:
746:
726:
646:
355:
234:
1431:
1369:
3730:
3630:
3366:
3280:
3039:
3029:
2968:
2925:
2757:
2747:
2716:
2616:
2588:
2431:
2421:
2220:
2092:
2062:
2047:
1832:
1790:
1785:
1657:
1548:
877:
862:
791:
754:
718:
707:
696:
676:
658:
330:
278:
272:
166:
162:
155:
45:
43:
were replaced (or initially supplemented) for astronomical use from 1952 onwards by an
3492:
3486:
3481:
3476:
3471:
3466:
3461:
3455:
3449:
3444:
3422:
3417:
3411:
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3389:
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3346:
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3118:
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2409:
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2303:
2293:
2283:
2165:
2009:
1935:
1884:
1837:
1752:
1712:
1707:
1702:
1282:
867:
616:
318:
215:
170:
103:
74:
729:
scales. Ephemeris Time was from 1952 to 1976 an official time scale standard of the
657:(which is the plane of the Earth's orbit around the sun). It has been superseded by
64:
The term "time" is generally used for many close but different concepts, including:
3301:
3265:
3152:
3147:
3142:
3129:
2868:
2483:
2477:
2143:
2077:
1999:
1930:
1879:
1727:
1667:
832:
822:
742:
359:
329:
deviates a fixed, round amount, usually a whole number of hours, from some form of
252:
195:
50:
1469:
1356:; Parry, J. V. L. (1958-08-01). "Frequency of Cesium in Terms of Ephemeris Time".
534:
521:
71:
as an object – one point on the time axis. Being an object, it has no value;
2532:
1116:
3783:
3275:
3270:
2915:
2898:
2830:
2810:
2696:
2578:
2493:
2471:
2378:
2363:
2158:
2138:
2128:
2057:
2014:
1994:
1923:
1742:
1644:
1353:
1087:
857:
847:
639:
308:
297:
268:
211:
247:(TAI) is the primary physically realized time standard. TAI is produced by the
3762:
3757:
3752:
3747:
3742:
3719:
3713:
3708:
3703:
3697:
3691:
3686:
3680:
3673:
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3648:
3643:
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3610:
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3593:
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3554:
3547:
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3535:
3528:
3522:
3342:
3290:
3243:
3227:
3113:
3019:
2840:
2701:
2671:
2609:
2388:
2288:
2195:
2170:
1973:
1757:
1377:
544:
344:
322:
95:
1517:
1447:
1385:
1321:
300:". To date these steps (and difference "TAI-UTC") have always been positive.
3776:
3187:
3024:
2908:
2883:
2863:
2780:
2732:
2726:
2711:
2451:
2368:
2004:
1916:
1891:
1872:
1762:
741:
second from 1956 to 1967, and it was also the source for calibration of the
684:
671:(RGO). The principal meridian of that observatory was chosen in 1884 by the
631:
326:
219:
203:
184:
1151:
957:
933:
IEC 60050-113:2011, item 113-01-013: "range of a time interval (113-01-10)"
1536:
1233:"IAU 2006 Resolution B3: Re-definition of Barycentric Dynamical Time, TDB"
999:
3222:
3202:
3044:
2950:
2850:
2641:
2636:
2019:
1780:
1772:
1630:
1620:
654:
606:
312:
78:
1177:"International Time Scales and the B.I.P.M. — Naval Oceanography Portal"
667:
was originally mean time deduced from meridian observations made at the
187:
at 12 hours ephemeris time". This definition was adopted as part of the
3217:
3207:
3137:
3009:
2920:
2785:
2358:
2348:
2270:
2261:
2246:
2148:
2133:
1978:
1901:
1610:
1439:
763:
For applications at the Earth's surface, ET's official replacement was
115:
68:
1527:
3212:
3162:
3157:
2456:
1615:
128:
3192:
3004:
2903:
2858:
2466:
2215:
1906:
1862:
1854:
1491:(3rd ed.). Mill Valley, California: University Science Books.
806:
334:
111:
36:
28:
206:
of the radiation corresponding to the transition between the two
3197:
3182:
3172:
2626:
2563:
1605:
1591:
1296:'Astronomy: Principles and Practice' (4th edition, 2003) at p.89
1091:
1040:
710:
such as UT0 and UT2 have been defined but are no longer in use.
635:
540:
526:
99:
3305:
2536:
1564:
924:
IEC 60050-113:2011, item 113-01-010; ISO 80000-3:2006, item 3–7
3177:
680:
558:× (JD − 2443144.5) × 86400 seconds, with the scale difference
137:
110:, which is a system of periodizing the events that shaped the
106:). One of the most important systems of periodization is the
81:
format, or more colloquially such as "today, 9:42 a.m.";
683:
is still in reality mean time at
Greenwich. Today, GMT is a
753:
DE200 (based on the JPL relativistic coordinate time scale
738:
590:
has been defined by the IAU to be 1.550519768e-08 exactly.
199:
2632:
International Earth
Rotation and Reference Systems Service
1537:
USNO article on the definition of seconds and leap seconds
202:
second, defined as exactly "the duration of 9,192,631,770
583:× (JD − 2443144.5) × 86400 seconds. The scale difference
285:(ERA) linearly scaled to match historical definitions of
1418:(1990). "Relativistic time scales in the solar system".
173:, and the ephemeris second was defined as "the fraction
1560:
1498:
P. K. Seidelmann, ed., University
Science Books, 1992,
358:
having its spatial origin at the center of mass of the
1530:
by
Demetrios Matsakis, Director, Time Service Dept.,
102:. Chronologies can be put into chronological groups (
1557:
Ask the
Experts – March 5, 2021. SCIENTIFIC AMERICAN
1202:"USNO GPS Time Transfer — Naval Oceanography Portal"
158:. MKS was adopted internationally during the 1940s.
3828:
3790:
3775:
3729:
3625:
3509:
3431:
3365:
3340:
3236:
3127:
3094:
3068:
2949:
2849:
2766:
2740:
2597:
2444:
2397:
2329:
2269:
2259:
2181:
2108:
2028:
1969:
1853:
1771:
1681:
1643:
1629:
1598:
1496:
Explanatory
Supplement to the Astronomical Almanac,
251:(BIPM), and is based on the combined input of many
1489:Explanatory Supplement to the Astronomical Almanac
1487:Urban, Sean; Seidelmann, P. Kenneth, eds. (2013).
311:worldwide, along with instructions for converting
714:Time standards for planetary motion calculations
27:Standardized time measurements are made using a
1307:
751:Jet Propulsion Laboratory Development Ephemeris
1322:"Time Scales: UT1, UTC, TAI, ET, TT, GPS time"
3317:
2548:
1576:
1227:
1225:
1171:
1169:
551:TCG is linearly related to TT as: TCG − TT =
8:
1283:"The Simpler Aspects of Celestial Mechanics"
249:International Bureau of Weights and Measures
1420:Celestial Mechanics and Dynamical Astronomy
1074:Time: From Earth Rotation to Atomic Physics
3362:
3324:
3310:
3302:
2555:
2541:
2533:
2266:
1640:
1583:
1569:
1561:
1285:, in Popular Astronomy 44 (1936), 533-541.
981:(ed. Ruth Northey), London 2012, p. 1131,
634:, sidereal time is used to predict when a
1468:vol.265 (1992), pages 833-838, including
1460:P K Seidelmann & T Fukushima (1992),
3086:International Commission on Stratigraphy
373:
263:directly but rather is a realization of
1472:, present and past, defined by the IAU.
899:
539:DTT = TT − TAI − 32.184 s published in
98:, an ordered sequence of events in the
594:Time standards based on Earth rotation
452:UT1 = TT − 32.184 s − DTT − LS + DUT1
412:TT = UT1 − DUT1 + LS + 32.184 s + DTT
1549:A history of astronomical time scales
7:
2517:
1337:UT2 is nowadays considered obsolete.
1076:. Weinheim: Wiley. pp. 231–232.
774:For the calculation of ephemerides,
286:
1010:from the original on March 12, 2015
520:LS = TAI − UTC = leap seconds from
129:Second § History of definition
1098:from the original on 17 April 2011
906:IEC 60050-113:2011, item 113-01-08
630:more than a mean sidereal day. In
572:TCB is a linear transformation of
362:, which is called the barycenter.
35:suspicions that the rate at which
14:
3357:Italics: historical or unofficial
2806:Discrete time and continuous time
1072:; Seidelmann, P. Kenneth (2009).
673:International Meridian Conference
607:plane of the orbit (the ecliptic)
2731:
2725:
2516:
2507:
2506:
1050:from the original on May 3, 2019
782:), and TDB has been replaced by
731:International Astronomical Union
16:Specification for measuring time
3820:Daylight saving time by country
1532:United States Naval Observatory
1265:"IAU (1991) RECOMMENDATION III"
1245:from the original on 2022-10-09
1088:"Base unit definitions: Second"
1004:United States Naval Observatory
455:UTC = TT − 32.184 s − DTT − LS
435:TT = UTC + LS + 32.184 s + DTT
2879:History of timekeeping devices
878:Orbital period as unit of time
183:of the tropical year for 1900
1:
792:JPL ephemeris time argument T
498:UT1 = GPS + 19 s − LS + DUT1
418:GPS = UT1 − DUT1 + LS − 19 s
189:International System of Units
1466:Astronomy & Astrophysics
703:and the sources they cite.)
2826:Gravitational time dilation
2662:Barycentric Coordinate Time
2321:Geological history of Earth
1308:Urban & Seidelmann 2013
1002:. Time Service Department,
790:(TCG), and redefined to be
784:Barycentric Coordinate Time
669:Royal Greenwich Observatory
352:Barycentric Coordinate Time
214:atom" (at a temperature of
210:of the ground state of the
144:both defined the second as
3878:
3333:Coordinated Universal Time
2682:Geocentric Coordinate Time
2667:Barycentric Dynamical Time
2605:Coordinated Universal Time
1673:Orders of magnitude (time)
1129:"BIPM - clock comparisons"
942:ISO 80000-3:2006, item 3–7
788:Geocentric Coordinate Time
776:Barycentric Dynamical Time
765:Terrestrial Dynamical Time
701:Coordinated Universal Time
689:Coordinated Universal Time
522:USNO Table of Leap Seconds
504:TT = GPS + 51.184 s + DTT
481:TT = TAI + 32.184 s + DTT
464:GPS = TT − 51.184 s − DTT
461:TAI = TT − 32.184 s − DTT
307:broadcasts a very precise
294:Coordinated Universal Time
231:Geocentric Coordinate Time
126:
2836:Time-translation symmetry
2723:
2647:International Atomic Time
2574:
2502:
2384:Time translation symmetry
1378:10.1103/PhysRevLett.1.105
805:(updated as from 2003 to
803:Jet Propulsion Laboratory
535:U.S. Naval Observatory EO
529:= UT1 − UTC published in
305:Global Positioning System
259:). TAI is not related to
245:International Atomic Time
123:Definitions of the second
3805:Time zones by UTC offset
952:U.S. Naval Observatory.
3836:Abolition of time zones
3815:Time zone abbreviations
3096:Astronomical chronology
3069:Archaeology and geology
2776:Absolute space and time
2692:IERS Reference Meridian
2687:International Date Line
2598:International standards
2339:Absolute space and time
1990:Astronomical chronology
1358:Physical Review Letters
1037:SI Brochure 8th Edition
979:Whitaker's Almanac 2013
2389:Time reversal symmetry
1693:Italian six-hour clock
1524:(get the current time)
1462:"Why new time scales?"
565:defined as 6.969290134
501:UTC = GPS + 19 s − LS
475:UT1 = TAI − LS + DUT1
441:GPS = UTC + LS − 19 s
415:TAI = UT1 − DUT1 + LS
226:Current time standards
3800:Time zones by country
3055:Weekday determination
2941:Sundial markup schema
2154:Time and fate deities
2099:The Unreality of Time
2038:A series and B series
1146:Matsakis, Demetrios.
828:Clock synchronization
809:) using as argument T
723:dynamical time scales
3351:Daylight saving time
3076:Chronological dating
2816:Theory of relativity
2677:Daylight saving time
2405:Chronological dating
2374:Theory of relativity
1718:Daylight saving time
1030:"SI Brochure (2006)"
743:caesium atomic clock
735:dynamical time scale
339:Daylight saving time
283:Earth Rotation Angle
3792:Lists of time zones
3286:Time value of money
3081:Geologic time scale
2936:History of sundials
2801:Cosmological decade
2753:Greenwich Mean Time
2584:Orders of magnitude
1698:Thai six-hour clock
1432:1990CeMDA..48...23B
1370:1958PhRvL...1..105M
1326:www.stjarnhimlen.se
1294:A E Roy, D Clarke,
1070:McCarthy, Dennis D.
873:Timekeeping on Mars
693:Greenwich Mean Time
665:Greenwich Mean Time
599:Apparent solar time
142:MKS system of units
108:geologic time scale
3810:Military time zone
3261:Mental chronometry
2889:Marine chronometer
2741:Obsolete standards
2228:Rosy retrospection
2206:Mental chronometry
2030:Philosophy of time
1542:2012-06-11 at the
1440:10.1007/BF00050674
1352:; Hall, R. Glenn;
843:Frequency standard
3844:
3843:
3771:
3770:
3299:
3298:
3109:Nuclear timescale
2791:Continuous signal
2530:
2529:
2440:
2439:
2415:Circadian rhythms
2233:Tense–aspect–mood
2088:Temporal finitism
1965:
1964:
1941:Grandfather clock
1520:according to the
1206:www.usno.navy.mil
1181:www.usno.navy.mil
1148:"Systems of time"
987:978-1-4081-7207-0
853:Time in astronomy
838:Epoch (astronomy)
514:
513:
507:TAI = GPS + 19 s
487:GPS = TAI − 19 s
449:Terrestrial Time
429:UT1 = UTC + DUT1
409:UTC = UT1 − DUT1
345:Julian day number
239:measurement error
3869:
3363:
3359:
3326:
3319:
3312:
3303:
3000:Dominical letter
2931:Equation of time
2894:Marine sandglass
2735:
2729:
2707:Terrestrial Time
2564:Time measurement
2557:
2550:
2543:
2534:
2520:
2519:
2510:
2509:
2427:Glottochronology
2267:
2183:Human experience
2043:B-theory of time
1641:
1585:
1578:
1571:
1562:
1492:
1473:
1458:
1452:
1451:
1408:
1402:
1396:
1390:
1389:
1346:
1340:
1339:
1334:
1332:
1320:Schlyter, Paul.
1317:
1311:
1305:
1299:
1292:
1286:
1281:See H A Harvey,
1279:
1273:
1272:
1261:
1255:
1254:
1252:
1250:
1244:
1237:
1229:
1220:
1219:
1214:
1212:
1198:
1192:
1191:
1189:
1187:
1173:
1164:
1163:
1161:
1159:
1150:. Archived from
1143:
1137:
1136:
1131:. Archived from
1125:
1119:
1114:
1108:
1107:
1105:
1103:
1084:
1078:
1077:
1066:
1060:
1059:
1057:
1055:
1049:
1034:
1026:
1020:
1019:
1017:
1015:
996:
990:
976:
970:
969:
967:
965:
956:. Archived from
949:
943:
940:
934:
931:
925:
922:
916:
913:
907:
904:
769:Terrestrial Time
651:equation of time
629:
628:
624:
611:Equation of time
568:
403:Mean Solar Time
374:
265:Terrestrial Time
208:hyperfine levels
198:for time is the
182:
181:
177:
153:
152:
148:
3877:
3876:
3872:
3871:
3870:
3868:
3867:
3866:
3847:
3846:
3845:
3840:
3824:
3786:
3767:
3725:
3621:
3505:
3427:
3355:
3354:
3341:
3336:
3330:
3300:
3295:
3232:
3123:
3090:
3064:
2945:
2845:
2796:Coordinate time
2768:Time in physics
2762:
2736:
2730:
2721:
2593:
2570:
2561:
2531:
2526:
2498:
2489:Time immemorial
2436:
2393:
2354:Coordinate time
2325:
2279:Geological time
2255:
2238:Time management
2201:Generation time
2185:
2177:
2122:
2104:
2024:
1983:
1961:
1849:
1767:
1684:
1677:
1633:
1625:
1594:
1589:
1544:Wayback Machine
1528:Systems of Time
1514:
1509:
1486:
1482:
1477:
1476:
1459:
1455:
1416:Kopejkin, S. M.
1412:Brumberg, V. A.
1410:
1409:
1405:
1397:
1393:
1348:
1347:
1343:
1330:
1328:
1319:
1318:
1314:
1306:
1302:
1293:
1289:
1280:
1276:
1263:
1262:
1258:
1248:
1246:
1242:
1235:
1231:
1230:
1223:
1210:
1208:
1200:
1199:
1195:
1185:
1183:
1175:
1174:
1167:
1157:
1155:
1145:
1144:
1140:
1127:
1126:
1122:
1115:
1111:
1101:
1099:
1086:
1085:
1081:
1068:
1067:
1063:
1053:
1051:
1047:
1043:. p. 112.
1032:
1028:
1027:
1023:
1013:
1011:
998:
997:
993:
977:
973:
963:
961:
951:
950:
946:
941:
937:
932:
928:
923:
919:
914:
910:
905:
901:
896:
891:
886:
819:
812:
800:
795:
781:
758:
747:coordinate time
727:coordinate time
716:
647:Mean solar time
638:will reach its
626:
622:
621:
596:
589:
588:
582:
581:
566:
564:
563:
557:
556:
545:TT(BIPM) tables
478:UTC = TAI − LS
438:TAI = UTC + LS
368:
356:coordinate time
287:mean solar time
235:coordinate time
228:
180:31,556,925.9747
179:
175:
174:
150:
146:
145:
131:
125:
62:
17:
12:
11:
5:
3875:
3873:
3865:
3864:
3859:
3849:
3848:
3842:
3841:
3839:
3838:
3832:
3830:
3829:Related topics
3826:
3825:
3823:
3822:
3817:
3812:
3807:
3802:
3796:
3794:
3788:
3787:
3782:
3780:
3773:
3772:
3769:
3768:
3766:
3765:
3760:
3755:
3750:
3745:
3739:
3737:
3727:
3726:
3724:
3723:
3716:
3711:
3706:
3701:
3694:
3689:
3684:
3677:
3670:
3665:
3658:
3651:
3646:
3641:
3635:
3633:
3623:
3622:
3620:
3619:
3614:
3607:
3602:
3597:
3590:
3585:
3580:
3575:
3570:
3563:
3558:
3551:
3544:
3539:
3532:
3525:
3519:
3517:
3507:
3506:
3504:
3503:
3496:
3489:
3484:
3479:
3474:
3469:
3464:
3459:
3452:
3447:
3441:
3439:
3429:
3428:
3426:
3425:
3420:
3415:
3408:
3403:
3398:
3393:
3386:
3381:
3375:
3373:
3360:
3338:
3337:
3331:
3329:
3328:
3321:
3314:
3306:
3297:
3296:
3294:
3293:
3288:
3283:
3281:Time metrology
3278:
3273:
3268:
3263:
3258:
3257:
3256:
3246:
3240:
3238:
3237:Related topics
3234:
3233:
3231:
3230:
3225:
3220:
3215:
3210:
3205:
3200:
3195:
3190:
3185:
3180:
3175:
3170:
3165:
3160:
3155:
3150:
3145:
3140:
3134:
3132:
3125:
3124:
3122:
3121:
3116:
3111:
3106:
3100:
3098:
3092:
3091:
3089:
3088:
3083:
3078:
3072:
3070:
3066:
3065:
3063:
3062:
3057:
3052:
3047:
3042:
3037:
3032:
3027:
3022:
3017:
3012:
3007:
3002:
2997:
2992:
2987:
2982:
2976:
2971:
2966:
2961:
2955:
2953:
2947:
2946:
2944:
2943:
2938:
2933:
2928:
2926:Dialing scales
2923:
2918:
2913:
2912:
2911:
2901:
2896:
2891:
2886:
2881:
2876:
2871:
2866:
2861:
2855:
2853:
2847:
2846:
2844:
2843:
2838:
2833:
2828:
2823:
2818:
2813:
2808:
2803:
2798:
2793:
2788:
2783:
2778:
2772:
2770:
2764:
2763:
2761:
2760:
2758:Prime meridian
2755:
2750:
2748:Ephemeris time
2744:
2742:
2738:
2737:
2724:
2722:
2720:
2719:
2717:180th meridian
2714:
2709:
2704:
2699:
2694:
2689:
2684:
2679:
2674:
2669:
2664:
2659:
2654:
2649:
2644:
2639:
2634:
2629:
2624:
2619:
2614:
2613:
2612:
2601:
2599:
2595:
2594:
2592:
2591:
2586:
2581:
2575:
2572:
2571:
2562:
2560:
2559:
2552:
2545:
2537:
2528:
2527:
2525:
2524:
2514:
2503:
2500:
2499:
2497:
2496:
2491:
2486:
2481:
2474:
2469:
2464:
2459:
2454:
2448:
2446:
2442:
2441:
2438:
2437:
2435:
2434:
2432:Time geography
2429:
2424:
2422:Clock reaction
2419:
2418:
2417:
2407:
2401:
2399:
2395:
2394:
2392:
2391:
2386:
2381:
2376:
2371:
2366:
2361:
2356:
2351:
2346:
2341:
2335:
2333:
2327:
2326:
2324:
2323:
2318:
2313:
2312:
2311:
2306:
2301:
2296:
2291:
2286:
2275:
2273:
2264:
2257:
2256:
2254:
2253:
2240:
2235:
2230:
2225:
2224:
2223:
2221:time signature
2218:
2208:
2203:
2198:
2192:
2190:
2179:
2178:
2176:
2175:
2174:
2173:
2163:
2162:
2161:
2151:
2146:
2141:
2136:
2131:
2125:
2123:
2121:
2120:
2115:
2109:
2106:
2105:
2103:
2102:
2095:
2093:Temporal parts
2090:
2085:
2080:
2075:
2070:
2065:
2063:Eternal return
2060:
2055:
2050:
2048:Chronocentrism
2045:
2040:
2034:
2032:
2026:
2025:
2023:
2022:
2017:
2012:
2007:
2002:
1997:
1992:
1986:
1984:
1982:
1981:
1976:
1970:
1967:
1966:
1963:
1962:
1960:
1959:
1958:
1957:
1943:
1938:
1933:
1928:
1927:
1926:
1921:
1920:
1919:
1914:
1904:
1899:
1894:
1889:
1888:
1887:
1877:
1876:
1875:
1859:
1857:
1851:
1850:
1848:
1847:
1840:
1835:
1833:Hindu Panchang
1830:
1825:
1820:
1815:
1810:
1805:
1800:
1799:
1798:
1793:
1788:
1777:
1775:
1769:
1768:
1766:
1765:
1760:
1755:
1750:
1745:
1740:
1735:
1730:
1725:
1720:
1715:
1710:
1705:
1700:
1695:
1689:
1687:
1679:
1678:
1676:
1675:
1670:
1665:
1660:
1655:
1649:
1647:
1638:
1627:
1626:
1624:
1623:
1618:
1613:
1608:
1602:
1600:
1596:
1595:
1590:
1588:
1587:
1580:
1573:
1565:
1559:
1558:
1552:
1551:by Steve Allen
1546:
1534:
1525:
1513:
1512:External links
1510:
1508:
1507:
1493:
1483:
1481:
1478:
1475:
1474:
1453:
1403:
1391:
1364:(3): 105–107.
1341:
1312:
1300:
1287:
1274:
1256:
1221:
1193:
1165:
1138:
1135:on 2019-08-10.
1120:
1109:
1079:
1061:
1021:
1000:"Leap Seconds"
991:
971:
954:"Leap Seconds"
944:
935:
926:
917:
908:
898:
897:
895:
892:
890:
887:
885:
882:
881:
880:
875:
870:
865:
863:Time metrology
860:
855:
850:
845:
840:
835:
830:
825:
818:
815:
810:
798:
793:
779:
756:
719:Ephemeris time
715:
712:
708:Universal Time
697:Universal Time
677:Prime Meridian
659:Universal Time
595:
592:
586:
584:
579:
577:
561:
559:
554:
552:
549:
548:
537:
531:IERS Bulletins
524:
512:
511:
508:
505:
502:
499:
496:
493:
489:
488:
485:
482:
479:
476:
473:
470:
466:
465:
462:
459:
456:
453:
450:
447:
443:
442:
439:
436:
433:
430:
427:
424:
420:
419:
416:
413:
410:
407:
404:
401:
397:
396:
393:
390:
387:
384:
381:
378:
367:
364:
331:Universal Time
279:Universal Time
273:mean sea level
227:
224:
167:ephemeris time
156:mean solar day
127:Main article:
124:
121:
120:
119:
93:
92:
91:
84:
83:
82:
61:
58:
46:ephemeris time
41:Earth rotation
15:
13:
10:
9:
6:
4:
3:
2:
3874:
3863:
3860:
3858:
3855:
3854:
3852:
3837:
3834:
3833:
3831:
3827:
3821:
3818:
3816:
3813:
3811:
3808:
3806:
3803:
3801:
3798:
3797:
3795:
3793:
3789:
3785:
3781:
3778:
3774:
3764:
3761:
3759:
3756:
3754:
3751:
3749:
3746:
3744:
3741:
3740:
3738:
3736:
3732:
3728:
3722:
3721:
3717:
3715:
3712:
3710:
3707:
3705:
3702:
3700:
3699:
3695:
3693:
3690:
3688:
3685:
3683:
3682:
3678:
3676:
3675:
3671:
3669:
3666:
3664:
3663:
3659:
3657:
3656:
3652:
3650:
3647:
3645:
3642:
3640:
3637:
3636:
3634:
3632:
3628:
3624:
3618:
3615:
3613:
3612:
3608:
3606:
3603:
3601:
3598:
3596:
3595:
3591:
3589:
3586:
3584:
3581:
3579:
3576:
3574:
3571:
3569:
3568:
3564:
3562:
3559:
3557:
3556:
3552:
3550:
3549:
3545:
3543:
3540:
3538:
3537:
3533:
3531:
3530:
3526:
3524:
3521:
3520:
3518:
3516:
3512:
3508:
3502:
3501:
3497:
3495:
3494:
3490:
3488:
3485:
3483:
3480:
3478:
3475:
3473:
3470:
3468:
3465:
3463:
3460:
3458:
3457:
3453:
3451:
3448:
3446:
3443:
3442:
3440:
3438:
3434:
3430:
3424:
3421:
3419:
3416:
3414:
3413:
3409:
3407:
3404:
3402:
3399:
3397:
3394:
3392:
3391:
3387:
3385:
3382:
3380:
3377:
3376:
3374:
3372:
3368:
3364:
3361:
3358:
3352:
3348:
3347:standard time
3344:
3339:
3334:
3327:
3322:
3320:
3315:
3313:
3308:
3307:
3304:
3292:
3289:
3287:
3284:
3282:
3279:
3277:
3274:
3272:
3269:
3267:
3264:
3262:
3259:
3255:
3252:
3251:
3250:
3247:
3245:
3242:
3241:
3239:
3235:
3229:
3226:
3224:
3221:
3219:
3216:
3214:
3211:
3209:
3206:
3204:
3201:
3199:
3196:
3194:
3191:
3189:
3186:
3184:
3181:
3179:
3176:
3174:
3171:
3169:
3166:
3164:
3161:
3159:
3156:
3154:
3151:
3149:
3146:
3144:
3141:
3139:
3136:
3135:
3133:
3131:
3130:units of time
3126:
3120:
3119:Sidereal time
3117:
3115:
3112:
3110:
3107:
3105:
3104:Galactic year
3102:
3101:
3099:
3097:
3093:
3087:
3084:
3082:
3079:
3077:
3074:
3073:
3071:
3067:
3061:
3060:Weekday names
3058:
3056:
3053:
3051:
3050:Tropical year
3048:
3046:
3043:
3041:
3038:
3036:
3033:
3031:
3028:
3026:
3023:
3021:
3018:
3016:
3015:Intercalation
3013:
3011:
3008:
3006:
3003:
3001:
2998:
2996:
2993:
2991:
2988:
2986:
2983:
2981:(lunar Hijri)
2980:
2977:
2975:
2972:
2970:
2967:
2965:
2962:
2960:
2957:
2956:
2954:
2952:
2948:
2942:
2939:
2937:
2934:
2932:
2929:
2927:
2924:
2922:
2919:
2917:
2914:
2910:
2907:
2906:
2905:
2902:
2900:
2897:
2895:
2892:
2890:
2887:
2885:
2882:
2880:
2877:
2875:
2872:
2870:
2867:
2865:
2862:
2860:
2857:
2856:
2854:
2852:
2848:
2842:
2839:
2837:
2834:
2832:
2829:
2827:
2824:
2822:
2821:Time dilation
2819:
2817:
2814:
2812:
2809:
2807:
2804:
2802:
2799:
2797:
2794:
2792:
2789:
2787:
2784:
2782:
2779:
2777:
2774:
2773:
2771:
2769:
2765:
2759:
2756:
2754:
2751:
2749:
2746:
2745:
2743:
2739:
2734:
2728:
2718:
2715:
2713:
2710:
2708:
2705:
2703:
2700:
2698:
2695:
2693:
2690:
2688:
2685:
2683:
2680:
2678:
2675:
2673:
2670:
2668:
2665:
2663:
2660:
2658:
2657:24-hour clock
2655:
2653:
2652:12-hour clock
2650:
2648:
2645:
2643:
2640:
2638:
2635:
2633:
2630:
2628:
2625:
2623:
2620:
2618:
2615:
2611:
2608:
2607:
2606:
2603:
2602:
2600:
2596:
2590:
2587:
2585:
2582:
2580:
2577:
2576:
2573:
2569:
2565:
2558:
2553:
2551:
2546:
2544:
2539:
2538:
2535:
2523:
2515:
2513:
2505:
2504:
2501:
2495:
2492:
2490:
2487:
2485:
2482:
2480:
2479:
2475:
2473:
2470:
2468:
2465:
2463:
2460:
2458:
2455:
2453:
2450:
2449:
2447:
2443:
2433:
2430:
2428:
2425:
2423:
2420:
2416:
2413:
2412:
2411:
2410:Chronobiology
2408:
2406:
2403:
2402:
2400:
2396:
2390:
2387:
2385:
2382:
2380:
2377:
2375:
2372:
2370:
2367:
2365:
2362:
2360:
2357:
2355:
2352:
2350:
2347:
2345:
2344:Arrow of time
2342:
2340:
2337:
2336:
2334:
2332:
2328:
2322:
2319:
2317:
2316:Geochronology
2314:
2310:
2307:
2305:
2302:
2300:
2297:
2295:
2292:
2290:
2287:
2285:
2282:
2281:
2280:
2277:
2276:
2274:
2272:
2268:
2265:
2263:
2258:
2252:
2248:
2244:
2241:
2239:
2236:
2234:
2231:
2229:
2226:
2222:
2219:
2217:
2214:
2213:
2212:
2209:
2207:
2204:
2202:
2199:
2197:
2194:
2193:
2191:
2189:
2184:
2180:
2172:
2169:
2168:
2167:
2166:Wheel of time
2164:
2160:
2157:
2156:
2155:
2152:
2150:
2147:
2145:
2142:
2140:
2137:
2135:
2132:
2130:
2127:
2126:
2124:
2119:
2116:
2114:
2111:
2110:
2107:
2101:
2100:
2096:
2094:
2091:
2089:
2086:
2084:
2081:
2079:
2076:
2074:
2071:
2069:
2066:
2064:
2061:
2059:
2056:
2054:
2051:
2049:
2046:
2044:
2041:
2039:
2036:
2035:
2033:
2031:
2027:
2021:
2018:
2016:
2013:
2011:
2010:Periodization
2008:
2006:
2003:
2001:
1998:
1996:
1993:
1991:
1988:
1987:
1985:
1980:
1977:
1975:
1972:
1971:
1968:
1956:
1955:
1951:
1950:
1949:
1948:
1944:
1942:
1939:
1937:
1936:Digital clock
1934:
1932:
1929:
1925:
1922:
1918:
1915:
1913:
1910:
1909:
1908:
1905:
1903:
1900:
1898:
1895:
1893:
1890:
1886:
1883:
1882:
1881:
1878:
1874:
1871:
1870:
1869:
1866:
1865:
1864:
1861:
1860:
1858:
1856:
1852:
1846:
1845:
1841:
1839:
1836:
1834:
1831:
1829:
1826:
1824:
1821:
1819:
1816:
1814:
1811:
1809:
1806:
1804:
1801:
1797:
1794:
1792:
1789:
1787:
1784:
1783:
1782:
1779:
1778:
1776:
1774:
1770:
1764:
1761:
1759:
1756:
1754:
1751:
1749:
1746:
1744:
1741:
1739:
1736:
1734:
1731:
1729:
1726:
1724:
1721:
1719:
1716:
1714:
1713:Relative hour
1711:
1709:
1708:24-hour clock
1706:
1704:
1703:12-hour clock
1701:
1699:
1696:
1694:
1691:
1690:
1688:
1686:
1680:
1674:
1671:
1669:
1666:
1664:
1661:
1659:
1656:
1654:
1651:
1650:
1648:
1646:
1642:
1639:
1637:
1632:
1628:
1622:
1619:
1617:
1614:
1612:
1609:
1607:
1604:
1603:
1601:
1597:
1593:
1586:
1581:
1579:
1574:
1572:
1567:
1566:
1563:
1556:
1553:
1550:
1547:
1545:
1541:
1538:
1535:
1533:
1529:
1526:
1523:
1519:
1516:
1515:
1511:
1505:
1504:0-935702-68-7
1501:
1497:
1494:
1490:
1485:
1484:
1479:
1471:
1467:
1463:
1457:
1454:
1449:
1445:
1441:
1437:
1433:
1429:
1425:
1421:
1417:
1413:
1407:
1404:
1400:
1395:
1392:
1387:
1383:
1379:
1375:
1371:
1367:
1363:
1359:
1355:
1351:
1350:Markowitz, W.
1345:
1342:
1338:
1327:
1323:
1316:
1313:
1310:, p. 81.
1309:
1304:
1301:
1297:
1291:
1288:
1284:
1278:
1275:
1270:
1266:
1260:
1257:
1241:
1238:. p. 2.
1234:
1228:
1226:
1222:
1218:
1207:
1203:
1197:
1194:
1182:
1178:
1172:
1170:
1166:
1154:on 2019-09-30
1153:
1149:
1142:
1139:
1134:
1130:
1124:
1121:
1118:
1113:
1110:
1097:
1093:
1089:
1083:
1080:
1075:
1071:
1065:
1062:
1046:
1042:
1038:
1031:
1025:
1022:
1009:
1005:
1001:
995:
992:
988:
984:
980:
975:
972:
960:on 2019-10-19
959:
955:
948:
945:
939:
936:
930:
927:
921:
918:
912:
909:
903:
900:
893:
888:
883:
879:
876:
874:
871:
869:
868:Time transfer
866:
864:
861:
859:
856:
854:
851:
849:
846:
844:
841:
839:
836:
834:
831:
829:
826:
824:
821:
820:
816:
814:
808:
804:
796:
789:
785:
777:
772:
770:
766:
761:
759:
752:
748:
744:
740:
736:
732:
728:
724:
720:
713:
711:
709:
704:
702:
698:
694:
690:
686:
682:
678:
674:
670:
666:
662:
660:
656:
652:
648:
644:
641:
640:highest point
637:
633:
618:
617:Sidereal time
614:
612:
608:
604:
600:
593:
591:
575:
570:
546:
542:
538:
536:
532:
528:
525:
523:
519:
518:
517:
516:Definitions:
509:
506:
503:
500:
497:
494:
491:
490:
486:
483:
480:
477:
474:
471:
468:
467:
463:
460:
457:
454:
451:
448:
445:
444:
440:
437:
434:
431:
428:
425:
422:
421:
417:
414:
411:
408:
405:
402:
399:
398:
394:
391:
388:
385:
382:
379:
376:
375:
372:
365:
363:
361:
357:
353:
349:
346:
342:
340:
336:
332:
328:
324:
320:
319:Standard time
316:
314:
310:
306:
301:
299:
295:
291:
288:
284:
281:(UT1) is the
280:
276:
274:
270:
266:
262:
258:
254:
253:atomic clocks
250:
246:
242:
240:
236:
232:
225:
223:
221:
217:
213:
209:
205:
201:
197:
192:
190:
186:
172:
171:tropical year
168:
164:
159:
157:
143:
139:
134:
130:
122:
117:
113:
109:
105:
104:periodization
101:
97:
94:
88:
87:
85:
80:
76:
73:
72:
70:
67:
66:
65:
59:
57:
54:
52:
48:
47:
42:
38:
32:
30:
25:
22:
21:time standard
3779:data sources
3718:
3696:
3679:
3672:
3660:
3653:
3609:
3592:
3565:
3553:
3546:
3534:
3527:
3498:
3491:
3454:
3410:
3388:
3356:
3266:Decimal time
2995:Astronomical
2874:Complication
2869:Atomic clock
2567:
2484:Time capsule
2478:Tempus fugit
2476:
2398:Other fields
2097:
2078:Perdurantism
2000:Calendar era
1952:
1945:
1931:Cuckoo clock
1868:astronomical
1842:
1668:Unit of time
1635:
1599:Key concepts
1518:Current time
1495:
1488:
1465:
1456:
1426:(1): 23–44.
1423:
1419:
1406:
1399:Wm Markowitz
1394:
1361:
1357:
1344:
1336:
1329:. Retrieved
1325:
1315:
1303:
1290:
1277:
1269:www.iers.org
1268:
1259:
1247:. Retrieved
1216:
1209:. Retrieved
1205:
1196:
1184:. Retrieved
1180:
1158:30 September
1156:. Retrieved
1152:the original
1141:
1133:the original
1123:
1112:
1100:. Retrieved
1082:
1073:
1064:
1052:. Retrieved
1036:
1024:
1014:November 22,
1012:. Retrieved
994:
978:
974:
962:. Retrieved
958:the original
947:
938:
929:
920:
911:
902:
833:Clock signal
823:Atomic clock
773:
762:
717:
706:Versions of
705:
663:
645:
615:
597:
571:
569:10 exactly.
550:
515:
472:Atomic Time
380:Description
369:
360:Solar System
350:
343:
317:
302:
292:
277:
243:
229:
218:and at mean
196:SI base unit
193:
163:Metrologists
160:
135:
132:
79:ISO standard
63:
55:
51:atomic clock
44:
33:
26:
20:
18:
3862:Timekeeping
3857:Time scales
3784:tz database
3276:System time
3271:Metric time
2990:Solar Hijri
2916:Water clock
2899:Radio clock
2831:Time domain
2811:Proper time
2697:Leap second
2579:Chronometry
2494:Time travel
2472:System time
2379:Time domain
2364:Proper time
2188:use of time
2159:Father Time
2139:Immortality
2129:Ages of Man
2058:Endurantism
2015:Regnal year
1995:Big History
1924:water-based
1823:Solar Hijri
1733:Hexadecimal
1683:Measurement
1645:Chronometry
1631:Measurement
858:Time signal
848:Radio clock
733:; it was a
426:Civil Time
366:Conversions
354:(TCB) is a
309:time signal
298:leap second
269:proper time
233:(TCG) is a
212:caesium-133
60:Terminology
3851:Categories
3343:UTC offset
3291:Timekeeper
3244:Chronology
3228:Millennium
3114:Precession
3020:Julian day
2841:T-symmetry
2702:Solar time
2672:Civil time
2196:Chronemics
2171:Kalachakra
2083:Presentism
2068:Eternalism
1974:Chronology
1912:mechanical
1863:Main types
1781:Main types
1522:bservatory
964:19 October
889:References
786:(TCB) and
725:and/or of
675:to be the
323:civil time
138:CGS system
96:chronology
3777:Time zone
3500:−00:25:21
3188:Fortnight
3035:Lunisolar
3025:Leap year
2959:Gregorian
2909:stopwatch
2884:Hourglass
2864:Astrarium
2781:Spacetime
2712:Time zone
2589:Metrology
2568:standards
2452:Leap year
2369:Spacetime
2243:Yesterday
2144:Dreamtime
2118:Mythology
2005:Deep time
1917:stopwatch
1892:hourglass
1873:astrarium
1803:Gregorian
1796:Lunisolar
1773:Calendars
1763:Time zone
1636:standards
1448:0923-2958
1386:0031-9007
1354:Essen, L.
1271:. Note 1.
894:Citations
685:time zone
632:astronomy
495:GPS Time
327:time zone
220:sea level
191:in 1960.
185:January 0
3249:Duration
3223:Saeculum
3203:Olympiad
3045:Solstice
2974:Holocene
2951:Calendar
2851:Horology
2642:ISO 8601
2637:ISO 31-1
2512:Category
2260:Time in
2251:Tomorrow
2113:Religion
2053:Duration
2020:Timeline
1954:Timeline
1753:Sidereal
1621:Eternity
1540:Archived
1331:21 March
1240:Archived
1211:23 March
1186:23 March
1096:Archived
1045:Archived
1008:Archived
817:See also
655:ecliptic
603:meridian
313:GPS time
216:0 K
169:and the
3218:Century
3208:Lustrum
3138:Instant
3010:Equinox
2979:Islamic
2921:Sundial
2786:Chronon
2522:Commons
2445:Related
2359:Instant
2349:Chronon
2331:Physics
2271:Geology
2262:science
2134:Destiny
1979:History
1947:History
1902:sundial
1885:quantum
1828:Chinese
1818:Islamic
1728:Decimal
1723:Chinese
1685:systems
1611:Present
1480:Sources
1428:Bibcode
1366:Bibcode
1249:4 April
1102:9 April
1054:May 23,
625:⁄
377:System
204:periods
178:⁄
149:⁄
116:history
69:instant
3763:+14:00
3758:+13:45
3753:+13:00
3748:+12:45
3743:+12:00
3720:+11:30
3714:+11:00
3709:+10:30
3704:+10:00
3698:+09:45
3692:+09:30
3687:+09:00
3681:+08:45
3674:+08:30
3668:+08:00
3662:+07:30
3655:+07:20
3649:+07:00
3644:+06:30
3639:+06:00
3617:+05:45
3611:+05:40
3605:+05:30
3600:+05:00
3594:+04:51
3588:+04:30
3583:+04:00
3578:+03:30
3573:+03:00
3567:+02:30
3561:+02:00
3555:+01:30
3548:+01:24
3542:+01:00
3536:+00:30
3529:+00:20
3523:+00:00
3493:−00:44
3487:−01:00
3482:−02:00
3477:−02:30
3472:−03:00
3467:−03:30
3462:−04:00
3456:−04:30
3450:−05:00
3445:−06:00
3423:−07:00
3418:−08:00
3412:−08:30
3406:−09:00
3401:−09:30
3396:−10:00
3390:−10:30
3384:−11:00
3379:−12:00
3213:Decade
3168:Moment
3163:Minute
3158:Second
3128:Other
2985:Julian
2964:Hebrew
2610:offset
2462:Moment
2457:Memory
2309:period
1897:marine
1880:atomic
1855:Clocks
1813:Hebrew
1808:Julian
1743:Metric
1616:Future
1502:
1446:
1384:
985:
771:(TT).
151:86,400
3353:(DST)
3335:(UTC)
3254:music
3193:Month
3153:Jiffy
3148:Shake
3143:Flick
3040:Solar
3030:Lunar
3005:Epact
2969:Hindu
2904:Watch
2859:Clock
2467:Space
2299:epoch
2289:chron
2247:Today
2216:tempo
2211:Music
2073:Event
1907:watch
1791:Lunar
1786:Solar
1758:Solar
1748:Roman
1738:Hindu
1243:(PDF)
1236:(PDF)
1048:(PDF)
1033:(PDF)
884:Notes
807:DE405
335:nadir
325:in a
154:of a
112:Earth
37:Earth
29:clock
3735:90°W
3731:180°
3631:180°
3627:90°E
3515:90°E
3433:90°W
3371:90°W
3369:to
3367:180°
3349:and
3345:for
3198:Year
3183:Week
3173:Hour
2627:DUT1
2566:and
2186:and
2149:Kāla
1844:List
1838:Maya
1634:and
1606:Past
1592:Time
1500:ISBN
1444:ISSN
1382:ISSN
1333:2022
1251:2022
1213:2022
1188:2022
1160:2019
1104:2011
1092:NIST
1056:2019
1041:BIPM
1016:2015
983:ISBN
966:2019
636:star
541:BIPM
527:DUT1
510:GPS
492:GPS
484:TAI
469:TAI
432:UTC
423:UTC
406:UT1
400:UT1
395:GPS
392:TAI
386:UTC
383:UT1
303:The
257:GNSS
140:and
100:past
90:end.
75:date
3733:to
3629:to
3513:to
3435:to
3178:Day
2304:era
2294:eon
2284:age
1663:TAI
1653:UTC
1436:doi
1374:doi
1117:TAI
811:eph
799:eph
794:eph
780:eph
760:).
757:eph
681:UT1
627:366
574:TDB
543:'s
533:or
458:TT
446:TT
389:TT
321:or
271:at
261:TCG
3853::
3511:0°
3437:0°
2622:ΔT
2617:UT
2249:–
2245:–
1658:UT
1464:,
1442:.
1434:.
1424:48
1422:.
1414:;
1380:.
1372:.
1360:.
1335:.
1324:.
1267:.
1224:^
1215:.
1204:.
1179:.
1168:^
1094:.
1090:.
1039:.
1035:.
1006:.
813:.
739:SI
699:,
695:,
661:.
341:.
275:.
241:.
200:SI
19:A
3325:e
3318:t
3311:v
2556:e
2549:t
2542:v
1584:e
1577:t
1570:v
1506:.
1450:.
1438::
1430::
1388:.
1376::
1368::
1362:1
1298:.
1253:.
1190:.
1162:.
1106:.
1058:.
1018:.
989:.
968:.
755:T
623:1
587:B
585:L
580:B
578:L
567:×
562:G
560:L
555:G
553:L
547:.
176:1
147:1
118:.
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.