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Diffstat (limited to 'contrib/tzdata/leap-seconds.list')
| -rw-r--r-- | contrib/tzdata/leap-seconds.list | 373 |
1 files changed, 119 insertions, 254 deletions
diff --git a/contrib/tzdata/leap-seconds.list b/contrib/tzdata/leap-seconds.list index 0f43115c8e53..e52effc257b2 100644 --- a/contrib/tzdata/leap-seconds.list +++ b/contrib/tzdata/leap-seconds.list @@ -1,255 +1,120 @@ +# ATOMIC TIME. +# The Coordinated Universal Time (UTC) is the reference time scale derived +# from The "Temps Atomique International" (TAI) calculated by the Bureau +# International des Poids et Mesures (BIPM) using a worldwide network of atomic +# clocks. UTC differs from TAI by an integer number of seconds; it is the basis +# of all activities in the world. # -# In the following text, the symbol '#' introduces -# a comment, which continues from that symbol until -# the end of the line. A plain comment line has a -# whitespace character following the comment indicator. -# There are also special comment lines defined below. -# A special comment will always have a non-whitespace -# character in column 2. -# -# A blank line should be ignored. -# -# The following table shows the corrections that must -# be applied to compute International Atomic Time (TAI) -# from the Coordinated Universal Time (UTC) values that -# are transmitted by almost all time services. -# -# The first column shows an epoch as a number of seconds -# since 1 January 1900, 00:00:00 (1900.0 is also used to -# indicate the same epoch.) Both of these time stamp formats -# ignore the complexities of the time scales that were -# used before the current definition of UTC at the start -# of 1972. (See note 3 below.) -# The second column shows the number of seconds that -# must be added to UTC to compute TAI for any timestamp -# at or after that epoch. The value on each line is -# valid from the indicated initial instant until the -# epoch given on the next one or indefinitely into the -# future if there is no next line. -# (The comment on each line shows the representation of -# the corresponding initial epoch in the usual -# day-month-year format. The epoch always begins at -# 00:00:00 UTC on the indicated day. See Note 5 below.) -# -# Important notes: -# -# 1. Coordinated Universal Time (UTC) is often referred to -# as Greenwich Mean Time (GMT). The GMT time scale is no -# longer used, and the use of GMT to designate UTC is -# discouraged. -# -# 2. The UTC time scale is realized by many national -# laboratories and timing centers. Each laboratory -# identifies its realization with its name: Thus -# UTC(NIST), UTC(USNO), etc. The differences among -# these different realizations are typically on the -# order of a few nanoseconds (i.e., 0.000 000 00x s) -# and can be ignored for many purposes. These differences -# are tabulated in Circular T, which is published monthly -# by the International Bureau of Weights and Measures -# (BIPM). See www.bipm.org for more information. -# -# 3. The current definition of the relationship between UTC -# and TAI dates from 1 January 1972. A number of different -# time scales were in use before that epoch, and it can be -# quite difficult to compute precise timestamps and time -# intervals in those "prehistoric" days. For more information, -# consult: -# -# The Explanatory Supplement to the Astronomical -# Ephemeris. -# or -# Terry Quinn, "The BIPM and the Accurate Measurement -# of Time," Proc. of the IEEE, Vol. 79, pp. 894-905, -# July, 1991. <http://dx.doi.org/10.1109/5.84965> -# reprinted in: -# Christine Hackman and Donald B Sullivan (eds.) -# Time and Frequency Measurement -# American Association of Physics Teachers (1996) -# <http://tf.nist.gov/general/pdf/1168.pdf>, pp. 75-86 -# -# 4. The decision to insert a leap second into UTC is currently -# the responsibility of the International Earth Rotation and -# Reference Systems Service. (The name was changed from the -# International Earth Rotation Service, but the acronym IERS -# is still used.) -# -# Leap seconds are announced by the IERS in its Bulletin C. -# -# See www.iers.org for more details. -# -# Every national laboratory and timing center uses the -# data from the BIPM and the IERS to construct UTC(lab), -# their local realization of UTC. -# -# Although the definition also includes the possibility -# of dropping seconds ("negative" leap seconds), this has -# never been done and is unlikely to be necessary in the -# foreseeable future. -# -# 5. If your system keeps time as the number of seconds since -# some epoch (e.g., NTP timestamps), then the algorithm for -# assigning a UTC time stamp to an event that happens during a positive -# leap second is not well defined. The official name of that leap -# second is 23:59:60, but there is no way of representing that time -# in these systems. -# Many systems of this type effectively stop the system clock for -# one second during the leap second and use a time that is equivalent -# to 23:59:59 UTC twice. For these systems, the corresponding TAI -# timestamp would be obtained by advancing to the next entry in the -# following table when the time equivalent to 23:59:59 UTC -# is used for the second time. Thus the leap second which -# occurred on 30 June 1972 at 23:59:59 UTC would have TAI -# timestamps computed as follows: -# -# ... -# 30 June 1972 23:59:59 (2287785599, first time): TAI= UTC + 10 seconds -# 30 June 1972 23:59:60 (2287785599,second time): TAI= UTC + 11 seconds -# 1 July 1972 00:00:00 (2287785600) TAI= UTC + 11 seconds -# ... -# -# If your system realizes the leap second by repeating 00:00:00 UTC twice -# (this is possible but not usual), then the advance to the next entry -# in the table must occur the second time that a time equivalent to -# 00:00:00 UTC is used. Thus, using the same example as above: -# -# ... -# 30 June 1972 23:59:59 (2287785599): TAI= UTC + 10 seconds -# 30 June 1972 23:59:60 (2287785600, first time): TAI= UTC + 10 seconds -# 1 July 1972 00:00:00 (2287785600,second time): TAI= UTC + 11 seconds -# ... -# -# in both cases the use of timestamps based on TAI produces a smooth -# time scale with no discontinuity in the time interval. However, -# although the long-term behavior of the time scale is correct in both -# methods, the second method is technically not correct because it adds -# the extra second to the wrong day. -# -# This complexity would not be needed for negative leap seconds (if they -# are ever used). The UTC time would skip 23:59:59 and advance from -# 23:59:58 to 00:00:00 in that case. The TAI offset would decrease by -# 1 second at the same instant. This is a much easier situation to deal -# with, since the difficulty of unambiguously representing the epoch -# during the leap second does not arise. -# -# Some systems implement leap seconds by amortizing the leap second -# over the last few minutes of the day. The frequency of the local -# clock is decreased (or increased) to realize the positive (or -# negative) leap second. This method removes the time step described -# above. Although the long-term behavior of the time scale is correct -# in this case, this method introduces an error during the adjustment -# period both in time and in frequency with respect to the official -# definition of UTC. -# -# Questions or comments to: -# Judah Levine -# Time and Frequency Division -# NIST -# Boulder, Colorado -# Judah.Levine@nist.gov -# -# Last Update of leap second values: 8 July 2016 -# -# The following line shows this last update date in NTP timestamp -# format. This is the date on which the most recent change to -# the leap second data was added to the file. This line can -# be identified by the unique pair of characters in the first two -# columns as shown below. -# -#$ 3676924800 -# -# The NTP timestamps are in units of seconds since the NTP epoch, -# which is 1 January 1900, 00:00:00. The Modified Julian Day number -# corresponding to the NTP time stamp, X, can be computed as -# -# X/86400 + 15020 -# -# where the first term converts seconds to days and the second -# term adds the MJD corresponding to the time origin defined above. -# The integer portion of the result is the integer MJD for that -# day, and any remainder is the time of day, expressed as the -# fraction of the day since 0 hours UTC. The conversion from day -# fraction to seconds or to hours, minutes, and seconds may involve -# rounding or truncation, depending on the method used in the -# computation. -# -# The data in this file will be updated periodically as new leap -# seconds are announced. In addition to being entered on the line -# above, the update time (in NTP format) will be added to the basic -# file name leap-seconds to form the name leap-seconds.<NTP TIME>. -# In addition, the generic name leap-seconds.list will always point to -# the most recent version of the file. -# -# This update procedure will be performed only when a new leap second -# is announced. -# -# The following entry specifies the expiration date of the data -# in this file in units of seconds since the origin at the instant -# 1 January 1900, 00:00:00. This expiration date will be changed -# at least twice per year whether or not a new leap second is -# announced. These semi-annual changes will be made no later -# than 1 June and 1 December of each year to indicate what -# action (if any) is to be taken on 30 June and 31 December, -# respectively. (These are the customary effective dates for new -# leap seconds.) This expiration date will be identified by a -# unique pair of characters in columns 1 and 2 as shown below. -# In the unlikely event that a leap second is announced with an -# effective date other than 30 June or 31 December, then this -# file will be edited to include that leap second as soon as it is -# announced or at least one month before the effective date -# (whichever is later). -# If an announcement by the IERS specifies that no leap second is -# scheduled, then only the expiration date of the file will -# be advanced to show that the information in the file is still -# current -- the update time stamp, the data and the name of the file -# will not change. -# -# Updated through IERS Bulletin C63 -# File expires on: 28 December 2022 -# -#@ 3881174400 -# -2272060800 10 # 1 Jan 1972 -2287785600 11 # 1 Jul 1972 -2303683200 12 # 1 Jan 1973 -2335219200 13 # 1 Jan 1974 -2366755200 14 # 1 Jan 1975 -2398291200 15 # 1 Jan 1976 -2429913600 16 # 1 Jan 1977 -2461449600 17 # 1 Jan 1978 -2492985600 18 # 1 Jan 1979 -2524521600 19 # 1 Jan 1980 -2571782400 20 # 1 Jul 1981 -2603318400 21 # 1 Jul 1982 -2634854400 22 # 1 Jul 1983 -2698012800 23 # 1 Jul 1985 -2776982400 24 # 1 Jan 1988 -2840140800 25 # 1 Jan 1990 -2871676800 26 # 1 Jan 1991 -2918937600 27 # 1 Jul 1992 -2950473600 28 # 1 Jul 1993 -2982009600 29 # 1 Jul 1994 -3029443200 30 # 1 Jan 1996 -3076704000 31 # 1 Jul 1997 -3124137600 32 # 1 Jan 1999 -3345062400 33 # 1 Jan 2006 -3439756800 34 # 1 Jan 2009 -3550089600 35 # 1 Jul 2012 -3644697600 36 # 1 Jul 2015 -3692217600 37 # 1 Jan 2017 -# -# the following special comment contains the -# hash value of the data in this file computed -# use the secure hash algorithm as specified -# by FIPS 180-1. See the files in ~/pub/sha for -# the details of how this hash value is -# computed. Note that the hash computation -# ignores comments and whitespace characters -# in data lines. It includes the NTP values -# of both the last modification time and the -# expiration time of the file, but not the -# white space on those lines. -# the hash line is also ignored in the -# computation. -# -#h 732b2044 5863a938 b7e43179 1339c710 ded63837 +# +# ASTRONOMICAL TIME (UT1) is the time scale based on the rate of rotation of the earth. +# It is now mainly derived from Very Long Baseline Interferometry (VLBI). The various +# irregular fluctuations progressively detected in the rotation rate of the Earth lead +# in 1972 to the replacement of UT1 by UTC as the reference time scale. +# +# +# LEAP SECOND +# Atomic clocks are more stable than the rate of the earth rotation since the latter +# undergoes a full range of geophysical perturbations at various time scales: lunisolar +# and core-mantle torques, atmospheric and oceanic effetcs, etc. +# Leap seconds are needed to keep the two time scales in agreement, i.e. UT1-UTC smaller +# than 0.9 second. Therefore, when necessary a "leap second" is applied to UTC. +# Since the adoption of this system in 1972 it has been necessary to add a number of seconds to UTC, +# firstly due to the initial choice of the value of the second (1/86400 mean solar day of +# the year 1820) and secondly to the general slowing down of the Earth's rotation. It is +# theorically possible to have a negative leap second (a second removed from UTC), but so far, +# all leap seconds have been positive (a second has been added to UTC). Based on what we know about +# the earth's rotation, it is unlikely that we will ever have a negative leap second. +# +# +# HISTORY +# The first leap second was added on June 30, 1972. Until yhe year 2000, it was necessary in average to add a +# leap second at a rate of 1 to 2 years. Since the year 2000 leap seconds are introduced with an +# average interval of 3 to 4 years due to the acceleration of the Earth rotation speed. +# +# +# RESPONSABILITY OF THE DECISION TO INTRODUCE A LEAP SECOND IN UTC +# The decision to introduce a leap second in UTC is the responsibility of the Earth Orientation Center of +# the International Earth Rotation and reference System Service (IERS). This center is located at Paris +# Observatory. According to international agreements, leap seconds should only be scheduled for certain dates: +# first preference is given to the end of December and June, and second preference at the end of March +# and September. Since the introduction of leap seconds in 1972, only dates in June and December were used. +# +# Questions or comments to: +# Christian Bizouard: christian.bizouard@obspm.fr +# Earth orientation Center of the IERS +# Paris Observatory, France +# +# +# +# COPYRIGHT STATUS OF THIS FILE +# This file is in the public domain. +# +# +# VALIDITY OF THE FILE +# It is important to express the validity of the file. These next two dates are +# given in units of seconds since 1900.0. +# +# 1) Last update of the file. +# +# Updated through IERS Bulletin C (https://hpiers.obspm.fr/iers/bul/bulc/bulletinc.dat) +# +# The following line shows the last update of this file in NTP timestamp: +# +#$ 3913697179 +# +# 2) Expiration date of the file given on a semi-annual basis: last June or last December +# +# File expires on 28 December 2024 +# +# Expire date in NTP timestamp: +# +#@ 3944332800 +# +# +# LIST OF LEAP SECONDS +# NTP timestamp (X parameter) is the number of seconds since 1900.0 +# +# MJD: The Modified Julian Day number. MJD = X/86400 + 15020 +# +# DTAI: The difference DTAI= TAI-UTC in units of seconds +# It is the quantity to add to UTC to get the time in TAI +# +# Day Month Year : epoch in clear +# +#NTP Time DTAI Day Month Year +# +2272060800 10 # 1 Jan 1972 +2287785600 11 # 1 Jul 1972 +2303683200 12 # 1 Jan 1973 +2335219200 13 # 1 Jan 1974 +2366755200 14 # 1 Jan 1975 +2398291200 15 # 1 Jan 1976 +2429913600 16 # 1 Jan 1977 +2461449600 17 # 1 Jan 1978 +2492985600 18 # 1 Jan 1979 +2524521600 19 # 1 Jan 1980 +2571782400 20 # 1 Jul 1981 +2603318400 21 # 1 Jul 1982 +2634854400 22 # 1 Jul 1983 +2698012800 23 # 1 Jul 1985 +2776982400 24 # 1 Jan 1988 +2840140800 25 # 1 Jan 1990 +2871676800 26 # 1 Jan 1991 +2918937600 27 # 1 Jul 1992 +2950473600 28 # 1 Jul 1993 +2982009600 29 # 1 Jul 1994 +3029443200 30 # 1 Jan 1996 +3076704000 31 # 1 Jul 1997 +3124137600 32 # 1 Jan 1999 +3345062400 33 # 1 Jan 2006 +3439756800 34 # 1 Jan 2009 +3550089600 35 # 1 Jul 2012 +3644697600 36 # 1 Jul 2015 +3692217600 37 # 1 Jan 2017 +# +# A hash code has been generated to be able to verify the integrity +# of this file. For more information about using this hash code, +# please see the readme file in the 'source' directory : +# https://hpiers.obspm.fr/iers/bul/bulc/ntp/sources/README +# +#h 9dac5845 8acd32c0 2947d462 daf4a943 f58d9391 |