leap-seconds.list revision 255902
1255902Sedwin# 2255902Sedwin# In the following text, the symbol '#' introduces 3255902Sedwin# a comment, which continues from that symbol until 4255902Sedwin# the end of the line. A plain comment line has a 5255902Sedwin# whitespace character following the comment indicator. 6255902Sedwin# There are also special comment lines defined below. 7255902Sedwin# A special comment will always have a non-whitespace 8255902Sedwin# character in column 2. 9255902Sedwin# 10255902Sedwin# A blank line should be ignored. 11255902Sedwin# 12255902Sedwin# The following table shows the corrections that must 13255902Sedwin# be applied to compute International Atomic Time (TAI) 14255902Sedwin# from the Coordinated Universal Time (UTC) values that 15255902Sedwin# are transmitted by almost all time services. 16255902Sedwin# 17255902Sedwin# The first column shows an epoch as a number of seconds 18255902Sedwin# since 1900.0 and the second column shows the number of 19255902Sedwin# seconds that must be added to UTC to compute TAI for 20255902Sedwin# any timestamp at or after that epoch. The value on 21255902Sedwin# each line is valid from the indicated initial instant 22255902Sedwin# until the epoch given on the next one or indefinitely 23255902Sedwin# into the future if there is no next line. 24255902Sedwin# (The comment on each line shows the representation of 25255902Sedwin# the corresponding initial epoch in the usual 26255902Sedwin# day-month-year format. The epoch always begins at 27255902Sedwin# 00:00:00 UTC on the indicated day. See Note 5 below.) 28255902Sedwin# 29255902Sedwin# Important notes: 30255902Sedwin# 31255902Sedwin# 1. Coordinated Universal Time (UTC) is often referred to 32255902Sedwin# as Greenwich Mean Time (GMT). The GMT time scale is no 33255902Sedwin# longer used, and the use of GMT to designate UTC is 34255902Sedwin# discouraged. 35255902Sedwin# 36255902Sedwin# 2. The UTC time scale is realized by many national 37255902Sedwin# laboratories and timing centers. Each laboratory 38255902Sedwin# identifies its realization with its name: Thus 39255902Sedwin# UTC(NIST), UTC(USNO), etc. The differences among 40255902Sedwin# these different realizations are typically on the 41255902Sedwin# order of a few nanoseconds (i.e., 0.000 000 00x s) 42255902Sedwin# and can be ignored for many purposes. These differences 43255902Sedwin# are tabulated in Circular T, which is published monthly 44255902Sedwin# by the International Bureau of Weights and Measures 45255902Sedwin# (BIPM). See www.bipm.fr for more information. 46255902Sedwin# 47255902Sedwin# 3. The current defintion of the relationship between UTC 48255902Sedwin# and TAI dates from 1 January 1972. A number of different 49255902Sedwin# time scales were in use before than epoch, and it can be 50255902Sedwin# quite difficult to compute precise timestamps and time 51255902Sedwin# intervals in those "prehistoric" days. For more information, 52255902Sedwin# consult: 53255902Sedwin# 54255902Sedwin# The Explanatory Supplement to the Astronomical 55255902Sedwin# Ephemeris. 56255902Sedwin# or 57255902Sedwin# Terry Quinn, "The BIPM and the Accurate Measurement 58255902Sedwin# of Time," Proc. of the IEEE, Vol. 79, pp. 894-905, 59255902Sedwin# July, 1991. 60255902Sedwin# 61255902Sedwin# 4. The insertion of leap seconds into UTC is currently the 62255902Sedwin# responsibility of the International Earth Rotation Service, 63255902Sedwin# which is located at the Paris Observatory: 64255902Sedwin# 65255902Sedwin# Central Bureau of IERS 66255902Sedwin# 61, Avenue de l'Observatoire 67255902Sedwin# 75014 Paris, France. 68255902Sedwin# 69255902Sedwin# Leap seconds are announced by the IERS in its Bulletin C 70255902Sedwin# 71255902Sedwin# See hpiers.obspm.fr or www.iers.org for more details. 72255902Sedwin# 73255902Sedwin# All national laboratories and timing centers use the 74255902Sedwin# data from the BIPM and the IERS to construct their 75255902Sedwin# local realizations of UTC. 76255902Sedwin# 77255902Sedwin# Although the definition also includes the possibility 78255902Sedwin# of dropping seconds ("negative" leap seconds), this has 79255902Sedwin# never been done and is unlikely to be necessary in the 80255902Sedwin# foreseeable future. 81255902Sedwin# 82255902Sedwin# 5. If your system keeps time as the number of seconds since 83255902Sedwin# some epoch (e.g., NTP timestamps), then the algorithm for 84255902Sedwin# assigning a UTC time stamp to an event that happens during a positive 85255902Sedwin# leap second is not well defined. The official name of that leap 86255902Sedwin# second is 23:59:60, but there is no way of representing that time 87255902Sedwin# in these systems. 88255902Sedwin# Many systems of this type effectively stop the system clock for 89255902Sedwin# one second during the leap second and use a time that is equivalent 90255902Sedwin# to 23:59:59 UTC twice. For these systems, the corresponding TAI 91255902Sedwin# timestamp would be obtained by advancing to the next entry in the 92255902Sedwin# following table when the time equivalent to 23:59:59 UTC 93255902Sedwin# is used for the second time. Thus the leap second which 94255902Sedwin# occurred on 30 June 1972 at 23:59:59 UTC would have TAI 95255902Sedwin# timestamps computed as follows: 96255902Sedwin# 97255902Sedwin# ... 98255902Sedwin# 30 June 1972 23:59:59 (2287785599, first time): TAI= UTC + 10 seconds 99255902Sedwin# 30 June 1972 23:59:60 (2287785599,second time): TAI= UTC + 11 seconds 100255902Sedwin# 1 July 1972 00:00:00 (2287785600) TAI= UTC + 11 seconds 101255902Sedwin# ... 102255902Sedwin# 103255902Sedwin# If your system realizes the leap second by repeating 00:00:00 UTC twice 104255902Sedwin# (this is possible but not usual), then the advance to the next entry 105255902Sedwin# in the table must occur the second time that a time equivlent to 106255902Sedwin# 00:00:00 UTC is used. Thus, using the same example as above: 107255902Sedwin# 108255902Sedwin# ... 109255902Sedwin# 30 June 1972 23:59:59 (2287785599): TAI= UTC + 10 seconds 110255902Sedwin# 30 June 1972 23:59:60 (2287785600, first time): TAI= UTC + 10 seconds 111255902Sedwin# 1 July 1972 00:00:00 (2287785600,second time): TAI= UTC + 11 seconds 112255902Sedwin# ... 113255902Sedwin# 114255902Sedwin# in both cases the use of timestamps based on TAI produces a smooth 115255902Sedwin# time scale with no discontinuity in the time interval. 116255902Sedwin# 117255902Sedwin# This complexity would not be needed for negative leap seconds (if they 118255902Sedwin# are ever used). The UTC time would skip 23:59:59 and advance from 119255902Sedwin# 23:59:58 to 00:00:00 in that case. The TAI offset would decrease by 120255902Sedwin# 1 second at the same instant. This is a much easier situation to deal 121255902Sedwin# with, since the difficulty of unambiguously representing the epoch 122255902Sedwin# during the leap second does not arise. 123255902Sedwin# 124255902Sedwin# Questions or comments to: 125255902Sedwin# Judah Levine 126255902Sedwin# Time and Frequency Division 127255902Sedwin# NIST 128255902Sedwin# Boulder, Colorado 129255902Sedwin# jlevine@boulder.nist.gov 130255902Sedwin# 131255902Sedwin# Last Update of leap second values: 11 January 2012 132255902Sedwin# 133255902Sedwin# The following line shows this last update date in NTP timestamp 134255902Sedwin# format. This is the date on which the most recent change to 135255902Sedwin# the leap second data was added to the file. This line can 136255902Sedwin# be identified by the unique pair of characters in the first two 137255902Sedwin# columns as shown below. 138255902Sedwin# 139255902Sedwin#$ 3535228800 140255902Sedwin# 141255902Sedwin# The NTP timestamps are in units of seconds since the NTP epoch, 142255902Sedwin# which is 1900.0. The Modified Julian Day number corresponding 143255902Sedwin# to the NTP time stamp, X, can be computed as 144255902Sedwin# 145255902Sedwin# X/86400 + 15020 146255902Sedwin# 147255902Sedwin# where the first term converts seconds to days and the second 148255902Sedwin# term adds the MJD corresponding to 1900.0. The integer portion 149255902Sedwin# of the result is the integer MJD for that day, and any remainder 150255902Sedwin# is the time of day, expressed as the fraction of the day since 0 151255902Sedwin# hours UTC. The conversion from day fraction to seconds or to 152255902Sedwin# hours, minutes, and seconds may involve rounding or truncation, 153255902Sedwin# depending on the method used in the computation. 154255902Sedwin# 155255902Sedwin# The data in this file will be updated periodically as new leap 156255902Sedwin# seconds are announced. In addition to being entered on the line 157255902Sedwin# above, the update time (in NTP format) will be added to the basic 158255902Sedwin# file name leap-seconds to form the name leap-seconds.<NTP TIME>. 159255902Sedwin# In addition, the generic name leap-seconds.list will always point to 160255902Sedwin# the most recent version of the file. 161255902Sedwin# 162255902Sedwin# This update procedure will be performed only when a new leap second 163255902Sedwin# is announced. 164255902Sedwin# 165255902Sedwin# The following entry specifies the expiration date of the data 166255902Sedwin# in this file in units of seconds since 1900.0. This expiration date 167255902Sedwin# will be changed at least twice per year whether or not a new leap 168255902Sedwin# second is announced. These semi-annual changes will be made no 169255902Sedwin# later than 1 June and 1 December of each year to indicate what 170255902Sedwin# action (if any) is to be taken on 30 June and 31 December, 171255902Sedwin# respectively. (These are the customary effective dates for new 172255902Sedwin# leap seconds.) This expiration date will be identified by a 173255902Sedwin# unique pair of characters in columns 1 and 2 as shown below. 174255902Sedwin# In the unlikely event that a leap second is announced with an 175255902Sedwin# effective date other than 30 June or 31 December, then this 176255902Sedwin# file will be edited to include that leap second as soon as it is 177255902Sedwin# announced or at least one month before the effective date 178255902Sedwin# (whichever is later). 179255902Sedwin# If an announcement by the IERS specifies that no leap second is 180255902Sedwin# scheduled, then only the expiration date of the file will 181255902Sedwin# be advanced to show that the information in the file is still 182255902Sedwin# current -- the update time stamp, the data and the name of the file 183255902Sedwin# will not change. 184255902Sedwin# 185255902Sedwin# Updated through IERS Bulletin C46 186255902Sedwin# File expires on: 28 June 2014 187255902Sedwin# 188255902Sedwin#@ 3612902400 189255902Sedwin# 190255902Sedwin2272060800 10 # 1 Jan 1972 191255902Sedwin2287785600 11 # 1 Jul 1972 192255902Sedwin2303683200 12 # 1 Jan 1973 193255902Sedwin2335219200 13 # 1 Jan 1974 194255902Sedwin2366755200 14 # 1 Jan 1975 195255902Sedwin2398291200 15 # 1 Jan 1976 196255902Sedwin2429913600 16 # 1 Jan 1977 197255902Sedwin2461449600 17 # 1 Jan 1978 198255902Sedwin2492985600 18 # 1 Jan 1979 199255902Sedwin2524521600 19 # 1 Jan 1980 200255902Sedwin2571782400 20 # 1 Jul 1981 201255902Sedwin2603318400 21 # 1 Jul 1982 202255902Sedwin2634854400 22 # 1 Jul 1983 203255902Sedwin2698012800 23 # 1 Jul 1985 204255902Sedwin2776982400 24 # 1 Jan 1988 205255902Sedwin2840140800 25 # 1 Jan 1990 206255902Sedwin2871676800 26 # 1 Jan 1991 207255902Sedwin2918937600 27 # 1 Jul 1992 208255902Sedwin2950473600 28 # 1 Jul 1993 209255902Sedwin2982009600 29 # 1 Jul 1994 210255902Sedwin3029443200 30 # 1 Jan 1996 211255902Sedwin3076704000 31 # 1 Jul 1997 212255902Sedwin3124137600 32 # 1 Jan 1999 213255902Sedwin3345062400 33 # 1 Jan 2006 214255902Sedwin3439756800 34 # 1 Jan 2009 215255902Sedwin3550089600 35 # 1 Jul 2012 216255902Sedwin# 217255902Sedwin# the following special comment contains the 218255902Sedwin# hash value of the data in this file computed 219255902Sedwin# use the secure hash algorithm as specified 220255902Sedwin# by FIPS 180-1. See the files in ~/pub/sha for 221255902Sedwin# the details of how this hash value is 222255902Sedwin# computed. Note that the hash computation 223255902Sedwin# ignores comments and whitespace characters 224255902Sedwin# in data lines. It includes the NTP values 225255902Sedwin# of both the last modification time and the 226255902Sedwin# expiration time of the file, but not the 227255902Sedwin# white space on those lines. 228255902Sedwin# the hash line is also ignored in the 229255902Sedwin# computation. 230255902Sedwin# 231255902Sedwin#h 1151a8f e85a5069 9000fcdb 3d5e5365 1d505b37 232