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diff --git a/tz/leap-seconds.list b/tz/leap-seconds.list new file mode 100644 index 0000000..3198d65 --- /dev/null +++ b/tz/leap-seconds.list @@ -0,0 +1,255 @@ +# +# 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 C61 +# File expires on: 28 December 2021 +# +#@ 3849638400 +# +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 2ab8253d d4380d28 75f01343 381504f8 8f8a4bfc |