leap-seconds.list revision 273438
1178354Ssam# 2178354Ssam# In the following text, the symbol '#' introduces 3178354Ssam# a comment, which continues from that symbol until 4178354Ssam# the end of the line. A plain comment line has a 5178354Ssam# whitespace character following the comment indicator. 6178354Ssam# There are also special comment lines defined below. 7178354Ssam# A special comment will always have a non-whitespace 8178354Ssam# character in column 2. 9178354Ssam# 10178354Ssam# A blank line should be ignored. 11178354Ssam# 12178354Ssam# The following table shows the corrections that must 13178354Ssam# be applied to compute International Atomic Time (TAI) 14178354Ssam# from the Coordinated Universal Time (UTC) values that 15178354Ssam# are transmitted by almost all time services. 16178354Ssam# 17178354Ssam# The first column shows an epoch as a number of seconds 18178354Ssam# since 1 January 1900, 00:00:00 (1900.0 is also used to 19178354Ssam# indicate the same epoch.) Both of these time stamp formats 20178354Ssam# ignore the complexities of the time scales that were 21178354Ssam# used before the current definition of UTC at the start 22178354Ssam# of 1972. (See note 3 below.) 23178354Ssam# The second column shows the number of seconds that 24178354Ssam# must be added to UTC to compute TAI for any timestamp 25178354Ssam# at or after that epoch. The value on each line is 26178354Ssam# valid from the indicated initial instant until the 27178354Ssam# epoch given on the next one or indefinitely into the 28178354Ssam# future if there is no next line. 29178354Ssam# (The comment on each line shows the representation of 30178354Ssam# the corresponding initial epoch in the usual 31178354Ssam# day-month-year format. The epoch always begins at 32178354Ssam# 00:00:00 UTC on the indicated day. See Note 5 below.) 33178354Ssam# 34178354Ssam# Important notes: 35178354Ssam# 36178354Ssam# 1. Coordinated Universal Time (UTC) is often referred to 37178354Ssam# as Greenwich Mean Time (GMT). The GMT time scale is no 38178354Ssam# longer used, and the use of GMT to designate UTC is 39178354Ssam# discouraged. 40178354Ssam# 41178354Ssam# 2. The UTC time scale is realized by many national 42178354Ssam# laboratories and timing centers. Each laboratory 43178354Ssam# identifies its realization with its name: Thus 44178354Ssam# UTC(NIST), UTC(USNO), etc. The differences among 45178354Ssam# these different realizations are typically on the 46178354Ssam# order of a few nanoseconds (i.e., 0.000 000 00x s) 47178354Ssam# and can be ignored for many purposes. These differences 48178354Ssam# are tabulated in Circular T, which is published monthly 49178354Ssam# by the International Bureau of Weights and Measures 50178354Ssam# (BIPM). See www.bipm.fr for more information. 51178354Ssam# 52178354Ssam# 3. The current definition of the relationship between UTC 53178354Ssam# and TAI dates from 1 January 1972. A number of different 54178354Ssam# time scales were in use before that epoch, and it can be 55178354Ssam# quite difficult to compute precise timestamps and time 56178354Ssam# intervals in those "prehistoric" days. For more information, 57178354Ssam# consult: 58178354Ssam# 59178354Ssam# The Explanatory Supplement to the Astronomical 60190391Ssam# Ephemeris. 61190391Ssam# or 62190391Ssam# Terry Quinn, "The BIPM and the Accurate Measurement 63178354Ssam# of Time," Proc. of the IEEE, Vol. 79, pp. 894-905, 64178354Ssam# July, 1991. 65178354Ssam# 66192468Ssam# 4. The decision to insert a leap second into UTC is currently 67178354Ssam# the responsibility of the International Earth Rotation and 68192468Ssam# Reference Systems Service. (The name was changed from the 69178354Ssam# International Earth Rotation Service, but the acronym IERS 70178354Ssam# is still used.) 71178354Ssam# 72178354Ssam# Leap seconds are announced by the IERS in its Bulletin C. 73178354Ssam# 74178354Ssam# See www.iers.org for more details. 75178354Ssam# 76178354Ssam# Every national laboratory and timing center uses the 77178354Ssam# data from the BIPM and the IERS to construct UTC(lab), 78178354Ssam# their local realization of UTC. 79178354Ssam# 80178354Ssam# Although the definition also includes the possibility 81178354Ssam# of dropping seconds ("negative" leap seconds), this has 82178354Ssam# never been done and is unlikely to be necessary in the 83178354Ssam# foreseeable future. 84178354Ssam# 85178354Ssam# 5. If your system keeps time as the number of seconds since 86178354Ssam# some epoch (e.g., NTP timestamps), then the algorithm for 87178354Ssam# assigning a UTC time stamp to an event that happens during a positive 88178354Ssam# leap second is not well defined. The official name of that leap 89178354Ssam# second is 23:59:60, but there is no way of representing that time 90178354Ssam# in these systems. 91178354Ssam# Many systems of this type effectively stop the system clock for 92178354Ssam# one second during the leap second and use a time that is equivalent 93178354Ssam# to 23:59:59 UTC twice. For these systems, the corresponding TAI 94178354Ssam# timestamp would be obtained by advancing to the next entry in the 95178354Ssam# following table when the time equivalent to 23:59:59 UTC 96178354Ssam# is used for the second time. Thus the leap second which 97178354Ssam# occurred on 30 June 1972 at 23:59:59 UTC would have TAI 98178354Ssam# timestamps computed as follows: 99178354Ssam# 100195379Ssam# ... 101195379Ssam# 30 June 1972 23:59:59 (2287785599, first time): TAI= UTC + 10 seconds 102195379Ssam# 30 June 1972 23:59:60 (2287785599,second time): TAI= UTC + 11 seconds 103195379Ssam# 1 July 1972 00:00:00 (2287785600) TAI= UTC + 11 seconds 104195379Ssam# ... 105195379Ssam# 106195379Ssam# If your system realizes the leap second by repeating 00:00:00 UTC twice 107195379Ssam# (this is possible but not usual), then the advance to the next entry 108195379Ssam# in the table must occur the second time that a time equivalent to 109195379Ssam# 00:00:00 UTC is used. Thus, using the same example as above: 110195379Ssam# 111195379Ssam# ... 112195379Ssam# 30 June 1972 23:59:59 (2287785599): TAI= UTC + 10 seconds 113195379Ssam# 30 June 1972 23:59:60 (2287785600, first time): TAI= UTC + 10 seconds 114195379Ssam# 1 July 1972 00:00:00 (2287785600,second time): TAI= UTC + 11 seconds 115195379Ssam# ... 116195379Ssam# 117195379Ssam# in both cases the use of timestamps based on TAI produces a smooth 118195379Ssam# time scale with no discontinuity in the time interval. However, 119195379Ssam# although the long-term behavior of the time scale is correct in both 120195379Ssam# methods, the second method is technically not correct because it adds 121195379Ssam# the extra second to the wrong day. 122178354Ssam# 123178354Ssam# This complexity would not be needed for negative leap seconds (if they 124178354Ssam# are ever used). The UTC time would skip 23:59:59 and advance from 125178354Ssam# 23:59:58 to 00:00:00 in that case. The TAI offset would decrease by 126178354Ssam# 1 second at the same instant. This is a much easier situation to deal 127178354Ssam# with, since the difficulty of unambiguously representing the epoch 128178354Ssam# during the leap second does not arise. 129178354Ssam# 130178354Ssam# Questions or comments to: 131178354Ssam# Judah Levine 132178354Ssam# Time and Frequency Division 133178354Ssam# NIST 134178354Ssam# Boulder, Colorado 135178354Ssam# Judah.Levine@nist.gov 136178354Ssam# 137178354Ssam# Last Update of leap second values: 11 January 2012 138178354Ssam# 139178354Ssam# The following line shows this last update date in NTP timestamp 140178354Ssam# format. This is the date on which the most recent change to 141178354Ssam# the leap second data was added to the file. This line can 142178354Ssam# be identified by the unique pair of characters in the first two 143178354Ssam# columns as shown below. 144178354Ssam# 145178354Ssam#$ 3535228800 146178354Ssam# 147178354Ssam# The NTP timestamps are in units of seconds since the NTP epoch, 148178354Ssam# which is 1 January 1900, 00:00:00. The Modified Julian Day number 149178354Ssam# corresponding to the NTP time stamp, X, can be computed as 150178354Ssam# 151178354Ssam# X/86400 + 15020 152178354Ssam# 153178354Ssam# where the first term converts seconds to days and the second 154178354Ssam# term adds the MJD corresponding to the time origin defined above. 155178354Ssam# The integer portion of the result is the integer MJD for that 156178354Ssam# day, and any remainder is the time of day, expressed as the 157178354Ssam# fraction of the day since 0 hours UTC. The conversion from day 158178354Ssam# fraction to seconds or to hours, minutes, and seconds may involve 159178354Ssam# rounding or truncation, depending on the method used in the 160178354Ssam# computation. 161178354Ssam# 162178354Ssam# The data in this file will be updated periodically as new leap 163178354Ssam# seconds are announced. In addition to being entered on the line 164178354Ssam# above, the update time (in NTP format) will be added to the basic 165178354Ssam# file name leap-seconds to form the name leap-seconds.<NTP TIME>. 166178354Ssam# In addition, the generic name leap-seconds.list will always point to 167178354Ssam# the most recent version of the file. 168178354Ssam# 169178354Ssam# This update procedure will be performed only when a new leap second 170178354Ssam# is announced. 171178354Ssam# 172178354Ssam# The following entry specifies the expiration date of the data 173178354Ssam# in this file in units of seconds since the origin at the instant 174178354Ssam# 1 January 1900, 00:00:00. This expiration date will be changed 175178354Ssam# at least twice per year whether or not a new leap second is 176178354Ssam# announced. These semi-annual changes will be made no later 177178354Ssam# than 1 June and 1 December of each year to indicate what 178178354Ssam# action (if any) is to be taken on 30 June and 31 December, 179178354Ssam# respectively. (These are the customary effective dates for new 180178354Ssam# leap seconds.) This expiration date will be identified by a 181178354Ssam# unique pair of characters in columns 1 and 2 as shown below. 182178354Ssam# In the unlikely event that a leap second is announced with an 183178354Ssam# effective date other than 30 June or 31 December, then this 184178354Ssam# file will be edited to include that leap second as soon as it is 185178354Ssam# announced or at least one month before the effective date 186178354Ssam# (whichever is later). 187178354Ssam# If an announcement by the IERS specifies that no leap second is 188178354Ssam# scheduled, then only the expiration date of the file will 189178354Ssam# be advanced to show that the information in the file is still 190178354Ssam# current -- the update time stamp, the data and the name of the file 191178354Ssam# will not change. 192178354Ssam# 193178354Ssam# Updated through IERS Bulletin C48 194178354Ssam# File expires on: 28 June 2015 195178354Ssam# 196178354Ssam#@ 3644438400 197178354Ssam# 198178354Ssam2272060800 10 # 1 Jan 1972 199178354Ssam2287785600 11 # 1 Jul 1972 200178354Ssam2303683200 12 # 1 Jan 1973 201178354Ssam2335219200 13 # 1 Jan 1974 202178354Ssam2366755200 14 # 1 Jan 1975 203178354Ssam2398291200 15 # 1 Jan 1976 204178354Ssam2429913600 16 # 1 Jan 1977 205178354Ssam2461449600 17 # 1 Jan 1978 206178354Ssam2492985600 18 # 1 Jan 1979 207178354Ssam2524521600 19 # 1 Jan 1980 208178354Ssam2571782400 20 # 1 Jul 1981 209178354Ssam2603318400 21 # 1 Jul 1982 210178354Ssam2634854400 22 # 1 Jul 1983 211178354Ssam2698012800 23 # 1 Jul 1985 212178354Ssam2776982400 24 # 1 Jan 1988 213178354Ssam2840140800 25 # 1 Jan 1990 214178354Ssam2871676800 26 # 1 Jan 1991 215178354Ssam2918937600 27 # 1 Jul 1992 216178354Ssam2950473600 28 # 1 Jul 1993 217178354Ssam2982009600 29 # 1 Jul 1994 218178354Ssam3029443200 30 # 1 Jan 1996 219178354Ssam3076704000 31 # 1 Jul 1997 220195379Ssam3124137600 32 # 1 Jan 1999 221178354Ssam3345062400 33 # 1 Jan 2006 222195379Ssam3439756800 34 # 1 Jan 2009 223195379Ssam3550089600 35 # 1 Jul 2012 224178354Ssam# 225178354Ssam# the following special comment contains the 226178354Ssam# hash value of the data in this file computed 227178354Ssam# use the secure hash algorithm as specified 228178354Ssam# by FIPS 180-1. See the files in ~/pub/sha for 229178354Ssam# the details of how this hash value is 230178354Ssam# computed. Note that the hash computation 231178354Ssam# ignores comments and whitespace characters 232178354Ssam# in data lines. It includes the NTP values 233178354Ssam# of both the last modification time and the 234178354Ssam# expiration time of the file, but not the 235178354Ssam# white space on those lines. 236178354Ssam# the hash line is also ignored in the 237178354Ssam# computation. 238178354Ssam# 239178354Ssam#h a4862ccd c6f43c6 964f3604 85944a26 b5cfad4e 240178354Ssam