Введение
Дополнительная секунда, вставленная для синхронизации гражданского времени с вращением Земли.
A leap second is a one second adjustment that is occasionally applied to Coordinated Universal Time (UTC), to accommodate the difference between precise time (International Atomic Time (TAI), as measured by atomic clocks) and imprecise observed solar time (UT1), which varies due to irregularities and long term slowdown in the Earth's rotation. The UTC time standard, widely used for international timekeeping and as the reference for civil time in most countries, uses TAI and consequently would run ahead of observed solar time unless it is reset to UT1 as needed. The leap second facility exists to provide this adjustment. The leap second was introduced in 1972. Since then, 27 leap seconds have been added to UTC, with the most recent occurring on December 31, 2016. Because the Earth's rotational speed varies in response to climatic and geological events, UTC leap seconds are irregularly spaced and unpredictable. Insertion of each UTC leap second is usually decided about six months in advance by the International Earth Rotation and Reference Systems Service (IERS), to ensure that the difference between the UTC and UT1 readings will never exceed 0.9 seconds. This practice has proven disruptive, particularly in the twenty first century and especially in services that depend on precise timestamping or time critical process control. And since not all computers are adjusted by leap second, they will display times differing from those that have been adjusted. After many years of discussions by different standards bodies, in November 2022, at the 27th General Conference on Weights and Measures, it was decided to abandon the leap second by or before 2035. Muslim scholars, including al Biruni in 1000, subdivided the mean solar day into 24 equinoctial hours, each of which was subdivided sexagesimally, that is into the units of minute, second, third, fourth and fifth, creating the modern second as of the mean solar day in the process. With this definition, the second was proposed in 1874 as the base unit of time in the CGS system of units. Soon afterwards Simon Newcomb and others discovered that Earth's rotation period varied irregularly, so in 1952, the International Astronomical Union (IAU) defined the second as a fraction of the sidereal year. In 1955, considering the tropical year to be more fundamental than the sidereal year, the IAU redefined the second as the fraction 1/31,556,925.975 of the 1900.0 mean tropical year. In 1956, a slightly more precise value of 1/31,556,925.9747 was adopted for the definition of the second by the International Committee for Weights and Measures, and in 1960 by the General Conference on Weights and Measures, becoming a part of the International System of Units (SI). Eventually, this definition too was found to be inadequate for precise time measurements, so in 1967, the SI second was again redefined as 9,192,631,770 periods of the radiation emitted by a caesium 133 atom in the transition between the two hyperfine levels of its ground state. That value agreed to 1 part in 1010 with the astronomical (ephemeris) second then in use. It was also close to 1/86,400 of the mean solar day as averaged between years 1750 and 1892. However, for the past several centuries, the length of the mean solar day has been increasing by about 1.4–1.7 ms per century, depending on the averaging time. By 1961, the mean solar day was already a millisecond or two longer than 86400 SI seconds. Therefore, time standards that change the date after precisely 86400 SI seconds, such as the International Atomic Time (TAI), would become increasingly ahead of time standards tied to the mean solar day, such as Universal Time (UT). When the Coordinated Universal Time (UTC) standard was instituted in 1960, based on atomic clocks, it was felt necessary to maintain agreement with UT, which, until then, had been the reference for broadcast time services. From 1960 to 1971, the rate of UTC atomic clocks was offset from a pure atomic time scale by the BIH to remain synchronized with UT2, a practice known as the "rubber second". The rate of UTC was decided at the start of each year, and was offset from the rate of atomic time by −150 parts per 10 for 1960–1962, by −130 parts per 10 for 1962–63, by −150 parts per 10 again for 1964–65, and by −300 parts per 10 for 1966–1971. Alongside the shift in rate, an occasional 0.1 s step (0.05 s before 1963) was needed. This predominantly frequency shifted rate of UTC was broadcast by MSF, WWV, and CHU among other time stations. In 1966, the CCIR approved "stepped atomic time" (SAT), which adjusted atomic time with more frequent 0.2 s adjustments to keep it within 0.1 s of UT2, because it had no rate adjustments. SAT was broadcast by WWVB among other time stations. |
! Year ! ! 30 Jun ! ! 31 Dec
|
! 1972
|bgcolor="lime"| +1 ||bgcolor="lime"| +1
|
! 1973
| 0 ||bgcolor="lime"| +1
|
! 1974
| 0 ||bgcolor="lime"| +1
|
! 1975
| 0 ||bgcolor="lime"| +1
|
! 1976
| 0 ||bgcolor="lime"| +1
|
! 1977
| 0 ||bgcolor="lime"| +1
|
! 1978
| 0 ||bgcolor="lime"| +1
|
! 1979
| 0 ||bgcolor="lime"| +1
|
! 1980
| 0 || 0
|
! 1981
|bgcolor="lime"| +1 || 0
|
! 1982
|bgcolor="lime"| +1 || 0
|
! 1983
|bgcolor="lime"| +1 || 0
|
! 1984
| 0 || 0
|
! 1985
|bgcolor="lime"| +1 || 0
|
! 1986
| 0 || 0
|
! 1987
| 0 ||bgcolor="lime"| +1
|
! 1988
| 0 || 0
|
! 1989
| 0 ||bgcolor="lime"| +1
|
! 1990
| 0 ||bgcolor="lime"| +1
|
! 1991
| 0 || 0
|
! 1992
|bgcolor="lime"| +1 || 0
|
! 1993
|bgcolor="lime"| +1 || 0
|
! 1994
|bgcolor="lime"| +1 || 0
|
! 1995
| 0 ||bgcolor="lime"| +1
|
! 1996
| 0 || 0
|
! 1997
|bgcolor="lime"| +1 || 0
|
! 1998
| 0 ||bgcolor="lime"| +1
|
! 1999
| 0 || 0
|
! 2000
| 0 || 0
|
! 2001
| 0 || 0
|
! 2002
| 0 || 0
|
! 2003
| 0 || 0
|
! 2004
| 0 || 0
|
! 2005
| 0 ||bgcolor="lime"| +1
|
! 2006
| 0 || 0
|
! 2007
| 0 || 0
|
! 2008
| 0 ||bgcolor="lime"| +1
|
! 2009
| 0 || 0
|
! 2010
| 0 || 0
|
! 2011
| 0 || 0
|
! 2012
|bgcolor="lime"| +1 || 0
|
! 2013
| 0 || 0
|
! 2014
| 0 || 0
|
! 2015
|bgcolor="lime"| +1 || 0
|
! 2016
| 0 ||bgcolor="lime"| +1
|
! 2017
| 0 || 0
|
! 2018
| 0 || 0
|
! 2019
| 0 || 0
|
! 2020
| 0 || 0
|
! 2021
| 0 || 0
|
! 2022
| 0 || 0
|
! 2023
| 0 || 0
|
! 2024
| 0 ||
|
! Year ! ! 30 Jun ! ! 31 Dec
|
!rowspan="2"| Total
| 11 || 16
|
|colspan="2"| 27
|
!colspan="3"| Current TAI − UTC
|
|colspan="3"| 37
|}
The scheduling of leap seconds was initially delegated to the Bureau International de l'Heure (BIH), but passed to the International Earth Rotation and Reference Systems Service (IERS) on 1 January 1988. IERS usually decides to apply a leap second whenever the difference between UTC and UT1 approaches 0.6 s, in order to keep the difference between UTC and UT1 from exceeding 0.9 s.
The UTC standard allows leap seconds to be applied at the end of any UTC month, with first preference to June and December and second preference to March and September. as of May 2023, all of them have been inserted at the end of either 30 June or 31 December. IERS publishes announcements every six months, whether leap seconds are to occur or not, in its "Bulletin C". Such announcements are typically published well in advance of each possible leap second date – usually in early January for 30 June and in early July for 31 December. Some time signal broadcasts give voice announcements of an impending leap second. Between 1972 and 2020, a leap second has been inserted about every 21 months, on average. However, the spacing is quite irregular and apparently increasing: there were no leap seconds in the six year interval between 1 January 1999 and 31 December 31, 2004 but there were nine leap seconds in the eight years 1972–1979. Since the introduction of leap seconds, 1972 has been the longest year on record: 366 days and two seconds. Unlike leap days, which begin after 28 February, 23:59:59 local time, UTC leap seconds occur simultaneously worldwide; for example, the leap second on 31 December 2005, 23:59:60 UTC was 31 December 2005, 18:59:60 (6:59:60 p. m.) in U. S. Eastern Standard Time and 1 January 2006, 08:59:60 (a. m.) in Japan Standard Time.
Високосная секунда — это односекундная корректировка, которая периодически применяется к Координированному универсальному времени (UTC), чтобы учесть разницу между точным временем (Международное атомное время (TAI), измеряемое атомными часами) и неточным наблюдаемым солнечным временем (UT1), которое изменяется из-за нерегулярностей и долгосрочного замедления вращения Земли. Стандарт времени UTC, широко используемый для международного отсчета времени и в качестве эталона для гражданского времени в большинстве стран, использует TAI и, следовательно, опережал бы наблюдаемое солнечное время, если бы не корректировался до UT1 по мере необходимости. Механизм високосной секунды существует для обеспечения этой корректировки. Високосная секунда была введена в 1972 году. С тех пор к UTC было добавлено 27 високосных секунд, последняя из которых произошла 31 декабря 2016 года. Поскольку скорость вращения Земли меняется в зависимости от климатических и геологических событий, високосные секунды UTC располагаются неравномерно и непредсказуемо. О вставке каждой високосной секунды UTC обычно решается примерно за шесть месяцев Международной службой по вращению Земли и системам отсчета (IERS), чтобы гарантировать, что разница между показаниями UTC и UT1 никогда не превысит 0,9 секунды. Эта практика оказалась проблематичной, особенно в двадцать первом веке и особенно в службах, зависящих от точного отметки времени или критически важного по времени управления процессами. Поскольку не все компьютеры корректируются с учетом високосной секунды, они будут отображать время, отличающееся от скорректированного. После многолетних обсуждений различными организациями по стандартизации, в ноябре 2022 года на 27-й Генеральной конференции по мерам и весам было принято решение отказаться от високосной секунды к 2035 году или ранее. Мусульманские ученые, включая аль-Бируни в 1000 году, разделили средний солнечный день на 24 равноденственных часа, каждый из которых был разделен по шестидесятеричной системе, то есть на минуты, секунды, третьи, четвертые и пятые, тем самым создав современную секунду как часть среднего солнечного дня. С этим определением секунда была предложена в 1874 году в качестве основной единицы времени в системе единиц CGS. Вскоре после этого Саймон Ньюкомб и другие обнаружили, что период вращения Земли меняется нерегулярно, поэтому в 1952 году Международный астрономический союз (IAU) определил секунду как долю звездного года. В 1955 году, считая тропический год более фундаментальным, чем звездный год, IAU переопределил секунду как долю 1/31 556 925,975 среднего тропического года 1900 года. В 1956 году Международный комитет по мерам и весам принял немного более точное значение 1/31 556 925,9747 для определения секунды, а в 1960 году Генеральная конференция по мерам и весам, включив ее в Международную систему единиц (СИ). В конечном итоге это определение также оказалось недостаточным для точных измерений времени, поэтому в 1967 году секунда СИ была вновь переопределена как 9 192 631 770 периодов излучения, испускаемого атомом цезия-133 при переходе между двумя сверхтонкими уровнями его основного состояния. Это значение соответствовало 1 части из 10^10 астрономической (эфемеридной) секунды, используемой в то время. Оно также было близко к 1/86 400 среднего солнечного дня, усредненного за период с 1750 по 1892 год. Однако за последние несколько столетий продолжительность среднего солнечного дня увеличивается примерно на 1,4–1,7 мс в столетие, в зависимости от времени усреднения. К 1961 году средний солнечный день уже был на одну-две миллисекунды длиннее 86 400 секунд СИ. Поэтому временные стандарты, которые меняют дату после точно 86 400 секунд СИ, такие как Международное атомное время (TAI), будут все больше опережать временные стандарты, связанные со средним солнечным днем, такие как Всемирное время (UT). Когда в 1960 году был введен стандарт Координированного универсального времени (UTC), основанный на атомных часах, было сочтено необходимым поддерживать согласованность с UT, который до этого времени был эталоном для служб радиовещания времени. С 1960 по 1971 год скорость атомных часов UTC была скорректирована относительно чистой атомной шкалы времени BIH, чтобы оставаться синхронизированной с UT2, что известно как "резиновая секунда". Скорость UTC определялась в начале каждого года и отличалась от скорости атомного времени на −150 частей на 10 для 1960–1962 годов, на −130 частей на 10 для 1962–1963 годов, на −150 частей на 10 снова для 1964–1965 годов и на −300 частей на 10 для 1966–1971 годов. Наряду со сдвигом скорости требовалась случайная корректировка на 0,1 с (0,05 с до 1963 года). Эта преимущественно частотно-смещенная скорость UTC транслировалась MSF, WWV и CHU, среди других станций времени. В 1966 году CCIR одобрил "ступенчатое атомное время" (SAT), которое корректировало атомное время с более частыми корректировками на 0,2 с, чтобы поддерживать его в пределах 0,1 с от UT2, поскольку оно не имело корректировок скорости. SAT транслировался WWVB, среди других станций времени.
A leap second is a one second adjustment that is occasionally applied to Coordinated Universal Time (UTC), to accommodate the difference between precise time (International Atomic Time (TAI), as measured by atomic clocks) and imprecise observed solar time (UT1), which varies due to irregularities and long term slowdown in the Earth's rotation. The UTC time standard, widely used for international timekeeping and as the reference for civil time in most countries, uses TAI and consequently would run ahead of observed solar time unless it is reset to UT1 as needed. The leap second facility exists to provide this adjustment. The leap second was introduced in 1972. Since then, 27 leap seconds have been added to UTC, with the most recent occurring on December 31, 2016. Because the Earth's rotational speed varies in response to climatic and geological events, UTC leap seconds are irregularly spaced and unpredictable. Insertion of each UTC leap second is usually decided about six months in advance by the International Earth Rotation and Reference Systems Service (IERS), to ensure that the difference between the UTC and UT1 readings will never exceed 0.9 seconds. This practice has proven disruptive, particularly in the twenty first century and especially in services that depend on precise timestamping or time critical process control. And since not all computers are adjusted by leap second, they will display times differing from those that have been adjusted. After many years of discussions by different standards bodies, in November 2022, at the 27th General Conference on Weights and Measures, it was decided to abandon the leap second by or before 2035. Muslim scholars, including al Biruni in 1000, subdivided the mean solar day into 24 equinoctial hours, each of which was subdivided sexagesimally, that is into the units of minute, second, third, fourth and fifth, creating the modern second as of the mean solar day in the process. With this definition, the second was proposed in 1874 as the base unit of time in the CGS system of units. Soon afterwards Simon Newcomb and others discovered that Earth's rotation period varied irregularly, so in 1952, the International Astronomical Union (IAU) defined the second as a fraction of the sidereal year. In 1955, considering the tropical year to be more fundamental than the sidereal year, the IAU redefined the second as the fraction 1/31,556,925.975 of the 1900.0 mean tropical year. In 1956, a slightly more precise value of 1/31,556,925.9747 was adopted for the definition of the second by the International Committee for Weights and Measures, and in 1960 by the General Conference on Weights and Measures, becoming a part of the International System of Units (SI). Eventually, this definition too was found to be inadequate for precise time measurements, so in 1967, the SI second was again redefined as 9,192,631,770 periods of the radiation emitted by a caesium 133 atom in the transition between the two hyperfine levels of its ground state. That value agreed to 1 part in 1010 with the astronomical (ephemeris) second then in use. It was also close to 1/86,400 of the mean solar day as averaged between years 1750 and 1892. However, for the past several centuries, the length of the mean solar day has been increasing by about 1.4–1.7 ms per century, depending on the averaging time. By 1961, the mean solar day was already a millisecond or two longer than 86400 SI seconds. Therefore, time standards that change the date after precisely 86400 SI seconds, such as the International Atomic Time (TAI), would become increasingly ahead of time standards tied to the mean solar day, such as Universal Time (UT). When the Coordinated Universal Time (UTC) standard was instituted in 1960, based on atomic clocks, it was felt necessary to maintain agreement with UT, which, until then, had been the reference for broadcast time services. From 1960 to 1971, the rate of UTC atomic clocks was offset from a pure atomic time scale by the BIH to remain synchronized with UT2, a practice known as the "rubber second". The rate of UTC was decided at the start of each year, and was offset from the rate of atomic time by −150 parts per 10 for 1960–1962, by −130 parts per 10 for 1962–63, by −150 parts per 10 again for 1964–65, and by −300 parts per 10 for 1966–1971. Alongside the shift in rate, an occasional 0.1 s step (0.05 s before 1963) was needed. This predominantly frequency shifted rate of UTC was broadcast by MSF, WWV, and CHU among other time stations. In 1966, the CCIR approved "stepped atomic time" (SAT), which adjusted atomic time with more frequent 0.2 s adjustments to keep it within 0.1 s of UT2, because it had no rate adjustments. SAT was broadcast by WWVB among other time stations. |
! Year ! ! 30 Jun ! ! 31 Dec
|
! 1972
|bgcolor="lime"| +1 ||bgcolor="lime"| +1
|
! 1973
| 0 ||bgcolor="lime"| +1
|
! 1974
| 0 ||bgcolor="lime"| +1
|
! 1975
| 0 ||bgcolor="lime"| +1
|
! 1976
| 0 ||bgcolor="lime"| +1
|
! 1977
| 0 ||bgcolor="lime"| +1
|
! 1978
| 0 ||bgcolor="lime"| +1
|
! 1979
| 0 ||bgcolor="lime"| +1
|
! 1980
| 0 || 0
|
! 1981
|bgcolor="lime"| +1 || 0
|
! 1982
|bgcolor="lime"| +1 || 0
|
! 1983
|bgcolor="lime"| +1 || 0
|
! 1984
| 0 || 0
|
! 1985
|bgcolor="lime"| +1 || 0
|
! 1986
| 0 || 0
|
! 1987
| 0 ||bgcolor="lime"| +1
|
! 1988
| 0 || 0
|
! 1989
| 0 ||bgcolor="lime"| +1
|
! 1990
| 0 ||bgcolor="lime"| +1
|
! 1991
| 0 || 0
|
! 1992
|bgcolor="lime"| +1 || 0
|
! 1993
|bgcolor="lime"| +1 || 0
|
! 1994
|bgcolor="lime"| +1 || 0
|
! 1995
| 0 ||bgcolor="lime"| +1
|
! 1996
| 0 || 0
|
! 1997
|bgcolor="lime"| +1 || 0
|
! 1998
| 0 ||bgcolor="lime"| +1
|
! 1999
| 0 || 0
|
! 2000
| 0 || 0
|
! 2001
| 0 || 0
|
! 2002
| 0 || 0
|
! 2003
| 0 || 0
|
! 2004
| 0 || 0
|
! 2005
| 0 ||bgcolor="lime"| +1
|
! 2006
| 0 || 0
|
! 2007
| 0 || 0
|
! 2008
| 0 ||bgcolor="lime"| +1
|
! 2009
| 0 || 0
|
! 2010
| 0 || 0
|
! 2011
| 0 || 0
|
! 2012
|bgcolor="lime"| +1 || 0
|
! 2013
| 0 || 0
|
! 2014
| 0 || 0
|
! 2015
|bgcolor="lime"| +1 || 0
|
! 2016
| 0 ||bgcolor="lime"| +1
|
! 2017
| 0 || 0
|
! 2018
| 0 || 0
|
! 2019
| 0 || 0
|
! 2020
| 0 || 0
|
! 2021
| 0 || 0
|
! 2022
| 0 || 0
|
! 2023
| 0 || 0
|
! 2024
| 0 ||
|
! Year ! ! 30 Jun ! ! 31 Dec
|
!rowspan="2"| Total
| 11 || 16
|
|colspan="2"| 27
|
!colspan="3"| Current TAI − UTC
|
|colspan="3"| 37
|}
The scheduling of leap seconds was initially delegated to the Bureau International de l'Heure (BIH), but passed to the International Earth Rotation and Reference Systems Service (IERS) on 1 January 1988. IERS usually decides to apply a leap second whenever the difference between UTC and UT1 approaches 0.6 s, in order to keep the difference between UTC and UT1 from exceeding 0.9 s.
The UTC standard allows leap seconds to be applied at the end of any UTC month, with first preference to June and December and second preference to March and September. as of May 2023, all of them have been inserted at the end of either 30 June or 31 December. IERS publishes announcements every six months, whether leap seconds are to occur or not, in its "Bulletin C". Such announcements are typically published well in advance of each possible leap second date – usually in early January for 30 June and in early July for 31 December. Some time signal broadcasts give voice announcements of an impending leap second. Between 1972 and 2020, a leap second has been inserted about every 21 months, on average. However, the spacing is quite irregular and apparently increasing: there were no leap seconds in the six year interval between 1 January 1999 and 31 December 31, 2004 but there were nine leap seconds in the eight years 1972–1979. Since the introduction of leap seconds, 1972 has been the longest year on record: 366 days and two seconds. Unlike leap days, which begin after 28 February, 23:59:59 local time, UTC leap seconds occur simultaneously worldwide; for example, the leap second on 31 December 2005, 23:59:60 UTC was 31 December 2005, 18:59:60 (6:59:60 p. m.) in U. S. Eastern Standard Time and 1 January 2006, 08:59:60 (a. m.) in Japan Standard Time.
| Год | 30 июня | 31 декабря |
|---|---|---|
| 1972 | +1 | +1 |
| 1973 | 0 | +1 |
| 1974 | 0 | +1 |
| 1975 | 0 | +1 |
| 1976 | 0 | +1 |
| 1977 | 0 | +1 |
| 1978 | 0 | +1 |
| 1979 | 0 | +1 |
| 1980 | 0 | 0 |
| 1981 | +1 | 0 |
| 1982 | +1 | 0 |
| 1983 | +1 | 0 |
| 1984 | 0 | 0 |
| 1985 | +1 | 0 |
| 1986 | 0 | 0 |
| 1987 | 0 | +1 |
| 1988 | 0 | 0 |
| 1989 | 0 | +1 |
| 1990 | 0 | +1 |
| 1991 | 0 | 0 |
| 1992 | +1 | 0 |
| 1993 | +1 | 0 |
| 1994 | +1 | 0 |
| 1995 | 0 | +1 |
| 1996 | 0 | 0 |
| 1997 | +1 | 0 |
| 1998 | 0 | +1 |
| 1999 | 0 | 0 |
| 2000 | 0 | 0 |
| 2001 | 0 | 0 |
| 2002 | 0 | 0 |
| 2003 | 0 | 0 |
| 2004 | 0 | 0 |
| 2005 | 0 | +1 |
| 2006 | 0 | 0 |
| 2007 | 0 | 0 |
| 2008 | 0 | +1 |
| 2009 | 0 | 0 |
| 2010 | 0 | 0 |
| 2011 | 0 | 0 |
| 2012 | +1 | 0 |
| 2013 | 0 | 0 |
| 2014 | 0 | 0 |
| 2015 | +1 | 0 |
| 2016 | 0 | +1 |
| 2017 | 0 | 0 |
| 2018 | 0 | 0 |
| 2019 | 0 | 0 |
| 2020 | 0 | 0 |
| 2021 | 0 | 0 |
| 2022 | 0 | 0 |
| 2023 | 0 | 0 |
| 2024 | 0 | |
A leap second is a one second adjustment that is occasionally applied to Coordinated Universal Time (UTC), to accommodate the difference between precise time (International Atomic Time (TAI), as measured by atomic clocks) and imprecise observed solar time (UT1), which varies due to irregularities and long term slowdown in the Earth's rotation. The UTC time standard, widely used for international timekeeping and as the reference for civil time in most countries, uses TAI and consequently would run ahead of observed solar time unless it is reset to UT1 as needed. The leap second facility exists to provide this adjustment. The leap second was introduced in 1972. Since then, 27 leap seconds have been added to UTC, with the most recent occurring on December 31, 2016. Because the Earth's rotational speed varies in response to climatic and geological events, UTC leap seconds are irregularly spaced and unpredictable. Insertion of each UTC leap second is usually decided about six months in advance by the International Earth Rotation and Reference Systems Service (IERS), to ensure that the difference between the UTC and UT1 readings will never exceed 0.9 seconds. This practice has proven disruptive, particularly in the twenty first century and especially in services that depend on precise timestamping or time critical process control. And since not all computers are adjusted by leap second, they will display times differing from those that have been adjusted. After many years of discussions by different standards bodies, in November 2022, at the 27th General Conference on Weights and Measures, it was decided to abandon the leap second by or before 2035. Muslim scholars, including al Biruni in 1000, subdivided the mean solar day into 24 equinoctial hours, each of which was subdivided sexagesimally, that is into the units of minute, second, third, fourth and fifth, creating the modern second as of the mean solar day in the process. With this definition, the second was proposed in 1874 as the base unit of time in the CGS system of units. Soon afterwards Simon Newcomb and others discovered that Earth's rotation period varied irregularly, so in 1952, the International Astronomical Union (IAU) defined the second as a fraction of the sidereal year. In 1955, considering the tropical year to be more fundamental than the sidereal year, the IAU redefined the second as the fraction 1/31,556,925.975 of the 1900.0 mean tropical year. In 1956, a slightly more precise value of 1/31,556,925.9747 was adopted for the definition of the second by the International Committee for Weights and Measures, and in 1960 by the General Conference on Weights and Measures, becoming a part of the International System of Units (SI). Eventually, this definition too was found to be inadequate for precise time measurements, so in 1967, the SI second was again redefined as 9,192,631,770 periods of the radiation emitted by a caesium 133 atom in the transition between the two hyperfine levels of its ground state. That value agreed to 1 part in 1010 with the astronomical (ephemeris) second then in use. It was also close to 1/86,400 of the mean solar day as averaged between years 1750 and 1892. However, for the past several centuries, the length of the mean solar day has been increasing by about 1.4–1.7 ms per century, depending on the averaging time. By 1961, the mean solar day was already a millisecond or two longer than 86400 SI seconds. Therefore, time standards that change the date after precisely 86400 SI seconds, such as the International Atomic Time (TAI), would become increasingly ahead of time standards tied to the mean solar day, such as Universal Time (UT). When the Coordinated Universal Time (UTC) standard was instituted in 1960, based on atomic clocks, it was felt necessary to maintain agreement with UT, which, until then, had been the reference for broadcast time services. From 1960 to 1971, the rate of UTC atomic clocks was offset from a pure atomic time scale by the BIH to remain synchronized with UT2, a practice known as the "rubber second". The rate of UTC was decided at the start of each year, and was offset from the rate of atomic time by −150 parts per 10 for 1960–1962, by −130 parts per 10 for 1962–63, by −150 parts per 10 again for 1964–65, and by −300 parts per 10 for 1966–1971. Alongside the shift in rate, an occasional 0.1 s step (0.05 s before 1963) was needed. This predominantly frequency shifted rate of UTC was broadcast by MSF, WWV, and CHU among other time stations. In 1966, the CCIR approved "stepped atomic time" (SAT), which adjusted atomic time with more frequent 0.2 s adjustments to keep it within 0.1 s of UT2, because it had no rate adjustments. SAT was broadcast by WWVB among other time stations. |
! Year ! ! 30 Jun ! ! 31 Dec
|
! 1972
|bgcolor="lime"| +1 ||bgcolor="lime"| +1
|
! 1973
| 0 ||bgcolor="lime"| +1
|
! 1974
| 0 ||bgcolor="lime"| +1
|
! 1975
| 0 ||bgcolor="lime"| +1
|
! 1976
| 0 ||bgcolor="lime"| +1
|
! 1977
| 0 ||bgcolor="lime"| +1
|
! 1978
| 0 ||bgcolor="lime"| +1
|
! 1979
| 0 ||bgcolor="lime"| +1
|
! 1980
| 0 || 0
|
! 1981
|bgcolor="lime"| +1 || 0
|
! 1982
|bgcolor="lime"| +1 || 0
|
! 1983
|bgcolor="lime"| +1 || 0
|
! 1984
| 0 || 0
|
! 1985
|bgcolor="lime"| +1 || 0
|
! 1986
| 0 || 0
|
! 1987
| 0 ||bgcolor="lime"| +1
|
! 1988
| 0 || 0
|
! 1989
| 0 ||bgcolor="lime"| +1
|
! 1990
| 0 ||bgcolor="lime"| +1
|
! 1991
| 0 || 0
|
! 1992
|bgcolor="lime"| +1 || 0
|
! 1993
|bgcolor="lime"| +1 || 0
|
! 1994
|bgcolor="lime"| +1 || 0
|
! 1995
| 0 ||bgcolor="lime"| +1
|
! 1996
| 0 || 0
|
! 1997
|bgcolor="lime"| +1 || 0
|
! 1998
| 0 ||bgcolor="lime"| +1
|
! 1999
| 0 || 0
|
! 2000
| 0 || 0
|
! 2001
| 0 || 0
|
! 2002
| 0 || 0
|
! 2003
| 0 || 0
|
! 2004
| 0 || 0
|
! 2005
| 0 ||bgcolor="lime"| +1
|
! 2006
| 0 || 0
|
! 2007
| 0 || 0
|
! 2008
| 0 ||bgcolor="lime"| +1
|
! 2009
| 0 || 0
|
! 2010
| 0 || 0
|
! 2011
| 0 || 0
|
! 2012
|bgcolor="lime"| +1 || 0
|
! 2013
| 0 || 0
|
! 2014
| 0 || 0
|
! 2015
|bgcolor="lime"| +1 || 0
|
! 2016
| 0 ||bgcolor="lime"| +1
|
! 2017
| 0 || 0
|
! 2018
| 0 || 0
|
! 2019
| 0 || 0
|
! 2020
| 0 || 0
|
! 2021
| 0 || 0
|
! 2022
| 0 || 0
|
! 2023
| 0 || 0
|
! 2024
| 0 ||
|
! Year ! ! 30 Jun ! ! 31 Dec
|
!rowspan="2"| Total
| 11 || 16
|
|colspan="2"| 27
|
!colspan="3"| Current TAI − UTC
|
|colspan="3"| 37
|}
The scheduling of leap seconds was initially delegated to the Bureau International de l'Heure (BIH), but passed to the International Earth Rotation and Reference Systems Service (IERS) on 1 January 1988. IERS usually decides to apply a leap second whenever the difference between UTC and UT1 approaches 0.6 s, in order to keep the difference between UTC and UT1 from exceeding 0.9 s.
The UTC standard allows leap seconds to be applied at the end of any UTC month, with first preference to June and December and second preference to March and September. as of May 2023, all of them have been inserted at the end of either 30 June or 31 December. IERS publishes announcements every six months, whether leap seconds are to occur or not, in its "Bulletin C". Such announcements are typically published well in advance of each possible leap second date – usually in early January for 30 June and in early July for 31 December. Some time signal broadcasts give voice announcements of an impending leap second. Between 1972 and 2020, a leap second has been inserted about every 21 months, on average. However, the spacing is quite irregular and apparently increasing: there were no leap seconds in the six year interval between 1 January 1999 and 31 December 31, 2004 but there were nine leap seconds in the eight years 1972–1979. Since the introduction of leap seconds, 1972 has been the longest year on record: 366 days and two seconds. Unlike leap days, which begin after 28 February, 23:59:59 local time, UTC leap seconds occur simultaneously worldwide; for example, the leap second on 31 December 2005, 23:59:60 UTC was 31 December 2005, 18:59:60 (6:59:60 p. m.) in U. S. Eastern Standard Time and 1 January 2006, 08:59:60 (a. m.) in Japan Standard Time.
Расписание високосных секунд первоначально было делегировано Бюро международных часов (BIH), но перешло в Международную службу по вращению Земли и системам отсчета (IERS) 1 января 1988 года. IERS обычно решает добавлять високосную секунду, когда разница между UTC и UT1 приближается к 0,6 с, чтобы разница между UTC и UT1 не превышала 0,9 с.
A leap second is a one second adjustment that is occasionally applied to Coordinated Universal Time (UTC), to accommodate the difference between precise time (International Atomic Time (TAI), as measured by atomic clocks) and imprecise observed solar time (UT1), which varies due to irregularities and long term slowdown in the Earth's rotation. The UTC time standard, widely used for international timekeeping and as the reference for civil time in most countries, uses TAI and consequently would run ahead of observed solar time unless it is reset to UT1 as needed. The leap second facility exists to provide this adjustment. The leap second was introduced in 1972. Since then, 27 leap seconds have been added to UTC, with the most recent occurring on December 31, 2016. Because the Earth's rotational speed varies in response to climatic and geological events, UTC leap seconds are irregularly spaced and unpredictable. Insertion of each UTC leap second is usually decided about six months in advance by the International Earth Rotation and Reference Systems Service (IERS), to ensure that the difference between the UTC and UT1 readings will never exceed 0.9 seconds. This practice has proven disruptive, particularly in the twenty first century and especially in services that depend on precise timestamping or time critical process control. And since not all computers are adjusted by leap second, they will display times differing from those that have been adjusted. After many years of discussions by different standards bodies, in November 2022, at the 27th General Conference on Weights and Measures, it was decided to abandon the leap second by or before 2035. Muslim scholars, including al Biruni in 1000, subdivided the mean solar day into 24 equinoctial hours, each of which was subdivided sexagesimally, that is into the units of minute, second, third, fourth and fifth, creating the modern second as of the mean solar day in the process. With this definition, the second was proposed in 1874 as the base unit of time in the CGS system of units. Soon afterwards Simon Newcomb and others discovered that Earth's rotation period varied irregularly, so in 1952, the International Astronomical Union (IAU) defined the second as a fraction of the sidereal year. In 1955, considering the tropical year to be more fundamental than the sidereal year, the IAU redefined the second as the fraction 1/31,556,925.975 of the 1900.0 mean tropical year. In 1956, a slightly more precise value of 1/31,556,925.9747 was adopted for the definition of the second by the International Committee for Weights and Measures, and in 1960 by the General Conference on Weights and Measures, becoming a part of the International System of Units (SI). Eventually, this definition too was found to be inadequate for precise time measurements, so in 1967, the SI second was again redefined as 9,192,631,770 periods of the radiation emitted by a caesium 133 atom in the transition between the two hyperfine levels of its ground state. That value agreed to 1 part in 1010 with the astronomical (ephemeris) second then in use. It was also close to 1/86,400 of the mean solar day as averaged between years 1750 and 1892. However, for the past several centuries, the length of the mean solar day has been increasing by about 1.4–1.7 ms per century, depending on the averaging time. By 1961, the mean solar day was already a millisecond or two longer than 86400 SI seconds. Therefore, time standards that change the date after precisely 86400 SI seconds, such as the International Atomic Time (TAI), would become increasingly ahead of time standards tied to the mean solar day, such as Universal Time (UT). When the Coordinated Universal Time (UTC) standard was instituted in 1960, based on atomic clocks, it was felt necessary to maintain agreement with UT, which, until then, had been the reference for broadcast time services. From 1960 to 1971, the rate of UTC atomic clocks was offset from a pure atomic time scale by the BIH to remain synchronized with UT2, a practice known as the "rubber second". The rate of UTC was decided at the start of each year, and was offset from the rate of atomic time by −150 parts per 10 for 1960–1962, by −130 parts per 10 for 1962–63, by −150 parts per 10 again for 1964–65, and by −300 parts per 10 for 1966–1971. Alongside the shift in rate, an occasional 0.1 s step (0.05 s before 1963) was needed. This predominantly frequency shifted rate of UTC was broadcast by MSF, WWV, and CHU among other time stations. In 1966, the CCIR approved "stepped atomic time" (SAT), which adjusted atomic time with more frequent 0.2 s adjustments to keep it within 0.1 s of UT2, because it had no rate adjustments. SAT was broadcast by WWVB among other time stations. |
! Year ! ! 30 Jun ! ! 31 Dec
|
! 1972
|bgcolor="lime"| +1 ||bgcolor="lime"| +1
|
! 1973
| 0 ||bgcolor="lime"| +1
|
! 1974
| 0 ||bgcolor="lime"| +1
|
! 1975
| 0 ||bgcolor="lime"| +1
|
! 1976
| 0 ||bgcolor="lime"| +1
|
! 1977
| 0 ||bgcolor="lime"| +1
|
! 1978
| 0 ||bgcolor="lime"| +1
|
! 1979
| 0 ||bgcolor="lime"| +1
|
! 1980
| 0 || 0
|
! 1981
|bgcolor="lime"| +1 || 0
|
! 1982
|bgcolor="lime"| +1 || 0
|
! 1983
|bgcolor="lime"| +1 || 0
|
! 1984
| 0 || 0
|
! 1985
|bgcolor="lime"| +1 || 0
|
! 1986
| 0 || 0
|
! 1987
| 0 ||bgcolor="lime"| +1
|
! 1988
| 0 || 0
|
! 1989
| 0 ||bgcolor="lime"| +1
|
! 1990
| 0 ||bgcolor="lime"| +1
|
! 1991
| 0 || 0
|
! 1992
|bgcolor="lime"| +1 || 0
|
! 1993
|bgcolor="lime"| +1 || 0
|
! 1994
|bgcolor="lime"| +1 || 0
|
! 1995
| 0 ||bgcolor="lime"| +1
|
! 1996
| 0 || 0
|
! 1997
|bgcolor="lime"| +1 || 0
|
! 1998
| 0 ||bgcolor="lime"| +1
|
! 1999
| 0 || 0
|
! 2000
| 0 || 0
|
! 2001
| 0 || 0
|
! 2002
| 0 || 0
|
! 2003
| 0 || 0
|
! 2004
| 0 || 0
|
! 2005
| 0 ||bgcolor="lime"| +1
|
! 2006
| 0 || 0
|
! 2007
| 0 || 0
|
! 2008
| 0 ||bgcolor="lime"| +1
|
! 2009
| 0 || 0
|
! 2010
| 0 || 0
|
! 2011
| 0 || 0
|
! 2012
|bgcolor="lime"| +1 || 0
|
! 2013
| 0 || 0
|
! 2014
| 0 || 0
|
! 2015
|bgcolor="lime"| +1 || 0
|
! 2016
| 0 ||bgcolor="lime"| +1
|
! 2017
| 0 || 0
|
! 2018
| 0 || 0
|
! 2019
| 0 || 0
|
! 2020
| 0 || 0
|
! 2021
| 0 || 0
|
! 2022
| 0 || 0
|
! 2023
| 0 || 0
|
! 2024
| 0 ||
|
! Year ! ! 30 Jun ! ! 31 Dec
|
!rowspan="2"| Total
| 11 || 16
|
|colspan="2"| 27
|
!colspan="3"| Current TAI − UTC
|
|colspan="3"| 37
|}
The scheduling of leap seconds was initially delegated to the Bureau International de l'Heure (BIH), but passed to the International Earth Rotation and Reference Systems Service (IERS) on 1 January 1988. IERS usually decides to apply a leap second whenever the difference between UTC and UT1 approaches 0.6 s, in order to keep the difference between UTC and UT1 from exceeding 0.9 s.
The UTC standard allows leap seconds to be applied at the end of any UTC month, with first preference to June and December and second preference to March and September. as of May 2023, all of them have been inserted at the end of either 30 June or 31 December. IERS publishes announcements every six months, whether leap seconds are to occur or not, in its "Bulletin C". Such announcements are typically published well in advance of each possible leap second date – usually in early January for 30 June and in early July for 31 December. Some time signal broadcasts give voice announcements of an impending leap second. Between 1972 and 2020, a leap second has been inserted about every 21 months, on average. However, the spacing is quite irregular and apparently increasing: there were no leap seconds in the six year interval between 1 January 1999 and 31 December 31, 2004 but there were nine leap seconds in the eight years 1972–1979. Since the introduction of leap seconds, 1972 has been the longest year on record: 366 days and two seconds. Unlike leap days, which begin after 28 February, 23:59:59 local time, UTC leap seconds occur simultaneously worldwide; for example, the leap second on 31 December 2005, 23:59:60 UTC was 31 December 2005, 18:59:60 (6:59:60 p. m.) in U. S. Eastern Standard Time and 1 January 2006, 08:59:60 (a. m.) in Japan Standard Time.
Стандарт UTC допускает добавление високосных секунд в конце любого месяца UTC, с предпочтением июня и декабря и вторичным предпочтением марта и сентября. По состоянию на май 2023 года все они были добавлены в конце 30 июня или 31 декабря. IERS публикует объявления каждые шесть месяцев, независимо от того, будут ли добавлены високосные секунды, в своем "Бюллетене C". Такие объявления обычно публикуются задолго до каждой возможной даты високосной секунды — обычно в начале января для 30 июня и в начале июля для 31 декабря. Некоторые радиосигналы времени объявляют о предстоящей високосной секунде. В период с 1972 по 2020 год високосная секунда добавлялась примерно каждые 21 месяц в среднем. Однако интервалы довольно нерегулярны и, по-видимому, увеличиваются: не было високосных секунд в шестилетний интервал между 1 января 1999 года и 31 декабря 2004 года, но было девять високосных секунд за восемь лет с 1972 по 1979 год. С момента введения високосных секунд 1972 год был самым продолжительным годом в истории: 366 дней и две секунды. В отличие от високосных дней, которые начинаются после 28 февраля 23:59:59 по местному времени, UTC...
A leap second is a one second adjustment that is occasionally applied to Coordinated Universal Time (UTC), to accommodate the difference between precise time (International Atomic Time (TAI), as measured by atomic clocks) and imprecise observed solar time (UT1), which varies due to irregularities and long term slowdown in the Earth's rotation. The UTC time standard, widely used for international timekeeping and as the reference for civil time in most countries, uses TAI and consequently would run ahead of observed solar time unless it is reset to UT1 as needed. The leap second facility exists to provide this adjustment. The leap second was introduced in 1972. Since then, 27 leap seconds have been added to UTC, with the most recent occurring on December 31, 2016. Because the Earth's rotational speed varies in response to climatic and geological events, UTC leap seconds are irregularly spaced and unpredictable. Insertion of each UTC leap second is usually decided about six months in advance by the International Earth Rotation and Reference Systems Service (IERS), to ensure that the difference between the UTC and UT1 readings will never exceed 0.9 seconds. This practice has proven disruptive, particularly in the twenty first century and especially in services that depend on precise timestamping or time critical process control. And since not all computers are adjusted by leap second, they will display times differing from those that have been adjusted. After many years of discussions by different standards bodies, in November 2022, at the 27th General Conference on Weights and Measures, it was decided to abandon the leap second by or before 2035. Muslim scholars, including al Biruni in 1000, subdivided the mean solar day into 24 equinoctial hours, each of which was subdivided sexagesimally, that is into the units of minute, second, third, fourth and fifth, creating the modern second as of the mean solar day in the process. With this definition, the second was proposed in 1874 as the base unit of time in the CGS system of units. Soon afterwards Simon Newcomb and others discovered that Earth's rotation period varied irregularly, so in 1952, the International Astronomical Union (IAU) defined the second as a fraction of the sidereal year. In 1955, considering the tropical year to be more fundamental than the sidereal year, the IAU redefined the second as the fraction 1/31,556,925.975 of the 1900.0 mean tropical year. In 1956, a slightly more precise value of 1/31,556,925.9747 was adopted for the definition of the second by the International Committee for Weights and Measures, and in 1960 by the General Conference on Weights and Measures, becoming a part of the International System of Units (SI). Eventually, this definition too was found to be inadequate for precise time measurements, so in 1967, the SI second was again redefined as 9,192,631,770 periods of the radiation emitted by a caesium 133 atom in the transition between the two hyperfine levels of its ground state. That value agreed to 1 part in 1010 with the astronomical (ephemeris) second then in use. It was also close to 1/86,400 of the mean solar day as averaged between years 1750 and 1892. However, for the past several centuries, the length of the mean solar day has been increasing by about 1.4–1.7 ms per century, depending on the averaging time. By 1961, the mean solar day was already a millisecond or two longer than 86400 SI seconds. Therefore, time standards that change the date after precisely 86400 SI seconds, such as the International Atomic Time (TAI), would become increasingly ahead of time standards tied to the mean solar day, such as Universal Time (UT). When the Coordinated Universal Time (UTC) standard was instituted in 1960, based on atomic clocks, it was felt necessary to maintain agreement with UT, which, until then, had been the reference for broadcast time services. From 1960 to 1971, the rate of UTC atomic clocks was offset from a pure atomic time scale by the BIH to remain synchronized with UT2, a practice known as the "rubber second". The rate of UTC was decided at the start of each year, and was offset from the rate of atomic time by −150 parts per 10 for 1960–1962, by −130 parts per 10 for 1962–63, by −150 parts per 10 again for 1964–65, and by −300 parts per 10 for 1966–1971. Alongside the shift in rate, an occasional 0.1 s step (0.05 s before 1963) was needed. This predominantly frequency shifted rate of UTC was broadcast by MSF, WWV, and CHU among other time stations. In 1966, the CCIR approved "stepped atomic time" (SAT), which adjusted atomic time with more frequent 0.2 s adjustments to keep it within 0.1 s of UT2, because it had no rate adjustments. SAT was broadcast by WWVB among other time stations. |
! Year ! ! 30 Jun ! ! 31 Dec
|
! 1972
|bgcolor="lime"| +1 ||bgcolor="lime"| +1
|
! 1973
| 0 ||bgcolor="lime"| +1
|
! 1974
| 0 ||bgcolor="lime"| +1
|
! 1975
| 0 ||bgcolor="lime"| +1
|
! 1976
| 0 ||bgcolor="lime"| +1
|
! 1977
| 0 ||bgcolor="lime"| +1
|
! 1978
| 0 ||bgcolor="lime"| +1
|
! 1979
| 0 ||bgcolor="lime"| +1
|
! 1980
| 0 || 0
|
! 1981
|bgcolor="lime"| +1 || 0
|
! 1982
|bgcolor="lime"| +1 || 0
|
! 1983
|bgcolor="lime"| +1 || 0
|
! 1984
| 0 || 0
|
! 1985
|bgcolor="lime"| +1 || 0
|
! 1986
| 0 || 0
|
! 1987
| 0 ||bgcolor="lime"| +1
|
! 1988
| 0 || 0
|
! 1989
| 0 ||bgcolor="lime"| +1
|
! 1990
| 0 ||bgcolor="lime"| +1
|
! 1991
| 0 || 0
|
! 1992
|bgcolor="lime"| +1 || 0
|
! 1993
|bgcolor="lime"| +1 || 0
|
! 1994
|bgcolor="lime"| +1 || 0
|
! 1995
| 0 ||bgcolor="lime"| +1
|
! 1996
| 0 || 0
|
! 1997
|bgcolor="lime"| +1 || 0
|
! 1998
| 0 ||bgcolor="lime"| +1
|
! 1999
| 0 || 0
|
! 2000
| 0 || 0
|
! 2001
| 0 || 0
|
! 2002
| 0 || 0
|
! 2003
| 0 || 0
|
! 2004
| 0 || 0
|
! 2005
| 0 ||bgcolor="lime"| +1
|
! 2006
| 0 || 0
|
! 2007
| 0 || 0
|
! 2008
| 0 ||bgcolor="lime"| +1
|
! 2009
| 0 || 0
|
! 2010
| 0 || 0
|
! 2011
| 0 || 0
|
! 2012
|bgcolor="lime"| +1 || 0
|
! 2013
| 0 || 0
|
! 2014
| 0 || 0
|
! 2015
|bgcolor="lime"| +1 || 0
|
! 2016
| 0 ||bgcolor="lime"| +1
|
! 2017
| 0 || 0
|
! 2018
| 0 || 0
|
! 2019
| 0 || 0
|
! 2020
| 0 || 0
|
! 2021
| 0 || 0
|
! 2022
| 0 || 0
|
! 2023
| 0 || 0
|
! 2024
| 0 ||
|
! Year ! ! 30 Jun ! ! 31 Dec
|
!rowspan="2"| Total
| 11 || 16
|
|colspan="2"| 27
|
!colspan="3"| Current TAI − UTC
|
|colspan="3"| 37
|}
The scheduling of leap seconds was initially delegated to the Bureau International de l'Heure (BIH), but passed to the International Earth Rotation and Reference Systems Service (IERS) on 1 January 1988. IERS usually decides to apply a leap second whenever the difference between UTC and UT1 approaches 0.6 s, in order to keep the difference between UTC and UT1 from exceeding 0.9 s.
The UTC standard allows leap seconds to be applied at the end of any UTC month, with first preference to June and December and second preference to March and September. as of May 2023, all of them have been inserted at the end of either 30 June or 31 December. IERS publishes announcements every six months, whether leap seconds are to occur or not, in its "Bulletin C". Such announcements are typically published well in advance of each possible leap second date – usually in early January for 30 June and in early July for 31 December. Some time signal broadcasts give voice announcements of an impending leap second. Between 1972 and 2020, a leap second has been inserted about every 21 months, on average. However, the spacing is quite irregular and apparently increasing: there were no leap seconds in the six year interval between 1 January 1999 and 31 December 31, 2004 but there were nine leap seconds in the eight years 1972–1979. Since the introduction of leap seconds, 1972 has been the longest year on record: 366 days and two seconds. Unlike leap days, which begin after 28 February, 23:59:59 local time, UTC leap seconds occur simultaneously worldwide; for example, the leap second on 31 December 2005, 23:59:60 UTC was 31 December 2005, 18:59:60 (6:59:60 p. m.) in U. S. Eastern Standard Time and 1 January 2006, 08:59:60 (a. m.) in Japan Standard Time.
Процесс
Когда это требуется, положительная високосная секунда вставляется между 23:59:59 выбранной даты по UTC и 00:00:00 следующей даты. Определение UTC указывает, что предпочтительными являются последний день декабря и июня, затем – последний день марта или сентября, и, в последнюю очередь, – последний день любого другого месяца. Все високосные секунды (по состоянию на 2019 год) были запланированы на 30 июня или 31 декабря. Дополнительная секунда отображается на часах UTC как 23:59:60. На часах, показывающих местное время, привязанное к UTC, високосная секунда может быть вставлена в конце другого часа (или получаса, или четверти часа), в зависимости от местного часового пояса. Отрицательная високосная секунда привела бы к исключению секунды 23:59:59 последнего дня выбранного месяца, так что за секундой 23:59:58 этой даты немедленно следовала бы секунда 00:00:00 следующей даты. С момента введения високосных секунд средние солнечные сутки опережали атомное время лишь в течение очень коротких периодов и не приводили к возникновению отрицательной високосной секунды.
Замедление вращения Земли
Высокосные секунды располагаются неравномерно, поскольку скорость вращения Земли меняется нерегулярно. Действительно, вращение Земли довольно непредсказуемо в долгосрочной перспективе, что объясняет, почему о високосных секундах объявляется лишь за шесть месяцев. Математическая модель вариаций длины солнечного дня была разработана Ф. Р. Стивенсоном и Л. В. Моррисоном.
Основная причина замедления вращения Земли – приливное трение, которое само по себе удлиняет день на 2,3 мс/век. Однако, ошибочно рассматривать високосные секунды как индикаторы замедления скорости вращения Земли; они являются индикаторами накопленной разницы между атомным временем и временем, определяемым вращением Земли. График в начале этого раздела показывает, что в 1972 году средняя продолжительность суток составляла приблизительно 86400,003 секунды, а в 2016 году – приблизительно 86400,001 секунды, что указывает на общее увеличение скорости вращения Земли за этот период. Положительные високосные секунды вводились в течение этого времени, поскольку среднегодовая продолжительность суток оставалась больше 86400 секунд СИ, а не из-за какого-либо замедления скорости вращения Земли. В 2021 году было сообщено, что Земля вращалась быстрее в 2020 году и пережила 28 самых коротких дней с 1960 года, каждый из которых длился менее 86399,999 секунды. Это побудило инженеров по всему миру обсудить отрицательную високосную секунду и другие возможные меры учёта времени, некоторые из которых могли бы упразднить високосные секунды.
Будущее високосных секунд
Временные шкалы TAI и UT1 точно определены: первая – атомными часами (и, следовательно, не зависит от вращения Земли), а вторая – астрономическими наблюдениями (измеряющими фактическое вращение планеты и, таким образом, солнечное время на Гринвичском меридиане). UTC (который обычно используется как основа для гражданского времени) является компромиссом: он ведется с использованием атомных секунд, но периодически корректируется вставкой високосной секунды для согласования с UT1. Неровность и непредсказуемость високосных секунд UTC создают проблемы для ряда областей, особенно в области вычислительной техники (см. ниже). В связи с растущими требованиями к точности меток времени в системах, таких как автоматизация процессов и высокочастотная торговля, это порождает ряд вопросов. В результате, устоявшаяся практика вставки високосных секунд пересматривается соответствующим международным органом по стандартизации.
Расчет разницы во времени и последовательность событий
Для вычисления прошедшего времени в секундах между двумя заданными датами UTC необходимо использовать таблицу високосных секунд, которую требуется обновлять каждый раз, когда объявляется новая високосная секунда. Поскольку информация о високосных секундах становится известна только за 6 месяцев до их введения, вычисление временных интервалов для дат UTC в более отдалённом будущем невозможно.
Отсутствие объявления о високосных секундах
Хотя BIPM объявляет о вставке секунды за 6 месяцев, большинство систем распространения времени (SNTP, IRIG B, PTP) сообщают о вставке секунды не более чем за 12 часов, иногда только за минуту до события, а некоторые даже не сообщают о ней вовсе (DNP 03).
Различия в применении
Не все часы реализуют скачковые секунды одинаково. В Unix-времени скачковые секунды обычно реализуются путем повторения 23:59:59 или добавления временной метки 23:59:60. Протокол сетевого времени (SNTP) останавливает время во время скачковой секунды, а некоторые серверы времени объявляют о "состоянии тревоги". Другие схемы "размазывают" время вблизи скачковой секунды, распределяя изменение времени на более длительный период. Это делается для того, чтобы избежать негативных последствий значительного (по современным меркам) скачка времени.
Текстовое представление високосной секунды
Текстовое представление високосной секунды определяется BIPM как "23:59:60". Существуют программы, которые не поддерживают этот формат и могут выдавать ошибку при работе с такими данными.
Бинарное представление високосной секунды
Большинство компьютерных операционных систем и большинство систем распространения времени представляют время в виде двоичного счетчика, указывающего количество секунд, прошедших с произвольной эпохи; например, с 1 января 1970 года 00:00:00 в системах POSIX или с 1 января 1900 года 00:00:00 в NTP. Этот счетчик не учитывает положительные високосные секунды и не содержит индикатора вставки високосной секунды, поэтому две последовательные секунды могут иметь одинаковое значение счетчика. Некоторые компьютерные операционные системы, в частности Linux, присваивают високосной секунде значение предыдущей секунды 23:59:59 (последовательность 59–59–0), в то время как другие компьютеры (и система распространения времени IRIG B) присваивают високосной секунде значение следующей секунды 00:00:00 (последовательность 59–0–0). Поскольку не существует стандарта, регулирующего эту последовательность, временные метки значений, полученных в точности в один и тот же момент времени, могут отличаться на одну секунду. Это может объяснять недостатки в системах, критичных ко времени, которые полагаются на значения с временными метками.
Обходные пути для задач с пересеченной секундой
Наиболее очевидным решением является использование шкалы TAI для всех операционных целей и преобразование в UTC для текста, удобного для чтения человеком. UTC всегда можно получить из TAI с помощью подходящей таблицы високосных секунд. Общество инженеров кино и телевидения (SMPTE) выбрало TAI для получения временных меток медиафайлов. IEC/IEEE 60802 (Временные сети) определяет TAI для всех операций. Автоматизация электросетей планирует перейти на TAI для глобального распространения событий в электрических сетях. Bluetooth Mesh также использует TAI. Вместо вставки високосной секунды в конце дня серверы Google реализуют "размытие високосной секунды", незначительно увеличивая продолжительность секунд в течение 24-часового периода, центрированного вокруг момента високосной секунды. Amazon последовал аналогичной, но несколько отличающейся схеме при введении високосной секунды 30 июня 2015 года, что привело к очередному случаю распространения различных шкал времени. Позже они выпустили NTP-сервис для экземпляров EC2, который выполняет размытие високосной секунды. UTC SLS был предложен как версия UTC с линейным размытием високосной секунды, но так и не стал стандартом. Было предложено, чтобы медиа-клиенты, использующие протокол Real time Transport Protocol, блокировали генерацию или использование NTP-меток времени во время високосной секунды и секунды, предшествующей ей. NIST создал специальный NTP-сервер времени для предоставления UT1 вместо UTC. Такой сервер будет особенно полезен в случае принятия резолюции МСЭ и прекращения вставки високосных секунд. Астрономические обсерватории и другие пользователи, которым требуется UT1, могут использовать UT1, хотя во многих случаях эти пользователи уже загружают UT1 UTC из IERS и применяют поправки в программном обеспечении.