2 # In the following text, the symbol '#' introduces
3 # a comment, which continues from that symbol until
4 # the end of the line. A plain comment line has a
5 # whitespace character following the comment indicator.
6 # There are also special comment lines defined below.
7 # A special comment will always have a non-whitespace
8 # character in column 2.
10 # A blank line should be ignored.
12 # The following table shows the corrections that must
13 # be applied to compute International Atomic Time (TAI)
14 # from the Coordinated Universal Time (UTC) values that
15 # are transmitted by almost all time services.
17 # The first column shows an epoch as a number of seconds
18 # since 1900.0 and the second column shows the number of
19 # seconds that must be added to UTC to compute TAI for
20 # any timestamp at or after that epoch. The value on
21 # each line is valid from the indicated initial instant
22 # until the epoch given on the next one or indefinitely
23 # into the future if there is no next line.
24 # (The comment on each line shows the representation of
25 # the corresponding initial epoch in the usual
26 # day-month-year format. The epoch always begins at
27 # 00:00:00 UTC on the indicated day. See Note 5 below.)
31 # 1. Coordinated Universal Time (UTC) is often referred to
32 # as Greenwich Mean Time (GMT). The GMT time scale is no
33 # longer used, and the use of GMT to designate UTC is
36 # 2. The UTC time scale is realized by many national
37 # laboratories and timing centers. Each laboratory
38 # identifies its realization with its name: Thus
39 # UTC(NIST), UTC(USNO), etc. The differences among
40 # these different realizations are typically on the
41 # order of a few nanoseconds (i.e., 0.000 000 00x s)
42 # and can be ignored for many purposes. These differences
43 # are tabulated in Circular T, which is published monthly
44 # by the International Bureau of Weights and Measures
45 # (BIPM). See www.bipm.fr for more information.
47 # 3. The current defintion of the relationship between UTC
48 # and TAI dates from 1 January 1972. A number of different
49 # time scales were in use before than epoch, and it can be
50 # quite difficult to compute precise timestamps and time
51 # intervals in those "prehistoric" days. For more information,
54 # The Explanatory Supplement to the Astronomical
57 # Terry Quinn, "The BIPM and the Accurate Measurement
58 # of Time," Proc. of the IEEE, Vol. 79, pp. 894-905,
61 # 4. The insertion of leap seconds into UTC is currently the
62 # responsibility of the International Earth Rotation Service,
63 # which is located at the Paris Observatory:
65 # Central Bureau of IERS
66 # 61, Avenue de l'Observatoire
67 # 75014 Paris, France.
69 # Leap seconds are announced by the IERS in its Bulletin C
71 # See hpiers.obspm.fr or www.iers.org for more details.
73 # All national laboratories and timing centers use the
74 # data from the BIPM and the IERS to construct their
75 # local realizations of UTC.
77 # Although the definition also includes the possibility
78 # of dropping seconds ("negative" leap seconds), this has
79 # never been done and is unlikely to be necessary in the
82 # 5. If your system keeps time as the number of seconds since
83 # some epoch (e.g., NTP timestamps), then the algorithm for
84 # assigning a UTC time stamp to an event that happens during a positive
85 # leap second is not well defined. The official name of that leap
86 # second is 23:59:60, but there is no way of representing that time
88 # Many systems of this type effectively stop the system clock for
89 # one second during the leap second and use a time that is equivalent
90 # to 23:59:59 UTC twice. For these systems, the corresponding TAI
91 # timestamp would be obtained by advancing to the next entry in the
92 # following table when the time equivalent to 23:59:59 UTC
93 # is used for the second time. Thus the leap second which
94 # occurred on 30 June 1972 at 23:59:59 UTC would have TAI
95 # timestamps computed as follows:
98 # 30 June 1972 23:59:59 (2287785599, first time): TAI= UTC + 10 seconds
99 # 30 June 1972 23:59:60 (2287785599,second time): TAI= UTC + 11 seconds
100 # 1 July 1972 00:00:00 (2287785600) TAI= UTC + 11 seconds
103 # If your system realizes the leap second by repeating 00:00:00 UTC twice
104 # (this is possible but not usual), then the advance to the next entry
105 # in the table must occur the second time that a time equivlent to
106 # 00:00:00 UTC is used. Thus, using the same example as above:
109 # 30 June 1972 23:59:59 (2287785599): TAI= UTC + 10 seconds
110 # 30 June 1972 23:59:60 (2287785600, first time): TAI= UTC + 10 seconds
111 # 1 July 1972 00:00:00 (2287785600,second time): TAI= UTC + 11 seconds
114 # in both cases the use of timestamps based on TAI produces a smooth
115 # time scale with no discontinuity in the time interval.
117 # This complexity would not be needed for negative leap seconds (if they
118 # are ever used). The UTC time would skip 23:59:59 and advance from
119 # 23:59:58 to 00:00:00 in that case. The TAI offset would decrease by
120 # 1 second at the same instant. This is a much easier situation to deal
121 # with, since the difficulty of unambiguously representing the epoch
122 # during the leap second does not arise.
124 # Questions or comments to:
126 # Time and Frequency Division
129 # jlevine@boulder.nist.gov
131 # Last Update of leap second values: 11 January 2012
133 # The following line shows this last update date in NTP timestamp
134 # format. This is the date on which the most recent change to
135 # the leap second data was added to the file. This line can
136 # be identified by the unique pair of characters in the first two
137 # columns as shown below.
141 # The NTP timestamps are in units of seconds since the NTP epoch,
142 # which is 1900.0. The Modified Julian Day number corresponding
143 # to the NTP time stamp, X, can be computed as
147 # where the first term converts seconds to days and the second
148 # term adds the MJD corresponding to 1900.0. The integer portion
149 # of the result is the integer MJD for that day, and any remainder
150 # is the time of day, expressed as the fraction of the day since 0
151 # hours UTC. The conversion from day fraction to seconds or to
152 # hours, minutes, and seconds may involve rounding or truncation,
153 # depending on the method used in the computation.
155 # The data in this file will be updated periodically as new leap
156 # seconds are announced. In addition to being entered on the line
157 # above, the update time (in NTP format) will be added to the basic
158 # file name leap-seconds to form the name leap-seconds.<NTP TIME>.
159 # In addition, the generic name leap-seconds.list will always point to
160 # the most recent version of the file.
162 # This update procedure will be performed only when a new leap second
165 # The following entry specifies the expiration date of the data
166 # in this file in units of seconds since 1900.0. This expiration date
167 # will be changed at least twice per year whether or not a new leap
168 # second is announced. These semi-annual changes will be made no
169 # later than 1 June and 1 December of each year to indicate what
170 # action (if any) is to be taken on 30 June and 31 December,
171 # respectively. (These are the customary effective dates for new
172 # leap seconds.) This expiration date will be identified by a
173 # unique pair of characters in columns 1 and 2 as shown below.
174 # In the unlikely event that a leap second is announced with an
175 # effective date other than 30 June or 31 December, then this
176 # file will be edited to include that leap second as soon as it is
177 # announced or at least one month before the effective date
178 # (whichever is later).
179 # If an announcement by the IERS specifies that no leap second is
180 # scheduled, then only the expiration date of the file will
181 # be advanced to show that the information in the file is still
182 # current -- the update time stamp, the data and the name of the file
185 # Updated through IERS Bulletin C46
186 # File expires on: 28 June 2014
190 2272060800 10 # 1 Jan 1972
191 2287785600 11 # 1 Jul 1972
192 2303683200 12 # 1 Jan 1973
193 2335219200 13 # 1 Jan 1974
194 2366755200 14 # 1 Jan 1975
195 2398291200 15 # 1 Jan 1976
196 2429913600 16 # 1 Jan 1977
197 2461449600 17 # 1 Jan 1978
198 2492985600 18 # 1 Jan 1979
199 2524521600 19 # 1 Jan 1980
200 2571782400 20 # 1 Jul 1981
201 2603318400 21 # 1 Jul 1982
202 2634854400 22 # 1 Jul 1983
203 2698012800 23 # 1 Jul 1985
204 2776982400 24 # 1 Jan 1988
205 2840140800 25 # 1 Jan 1990
206 2871676800 26 # 1 Jan 1991
207 2918937600 27 # 1 Jul 1992
208 2950473600 28 # 1 Jul 1993
209 2982009600 29 # 1 Jul 1994
210 3029443200 30 # 1 Jan 1996
211 3076704000 31 # 1 Jul 1997
212 3124137600 32 # 1 Jan 1999
213 3345062400 33 # 1 Jan 2006
214 3439756800 34 # 1 Jan 2009
215 3550089600 35 # 1 Jul 2012
217 # the following special comment contains the
218 # hash value of the data in this file computed
219 # use the secure hash algorithm as specified
220 # by FIPS 180-1. See the files in ~/pub/sha for
221 # the details of how this hash value is
222 # computed. Note that the hash computation
223 # ignores comments and whitespace characters
224 # in data lines. It includes the NTP values
225 # of both the last modification time and the
226 # expiration time of the file, but not the
227 # white space on those lines.
228 # the hash line is also ignored in the
231 #h 1151a8f e85a5069 9000fcdb 3d5e5365 1d505b37