4 # In the following text, the symbol '#' introduces
5 # a comment, which continues from that symbol until
6 # the end of the line. A plain comment line has a
7 # whitespace character following the comment indicator.
8 # There are also special comment lines defined below.
9 # A special comment will always have a non-whitespace
10 # character in column 2.
12 # A blank line should be ignored.
14 # The following table shows the corrections that must
15 # be applied to compute International Atomic Time (TAI)
16 # from the Coordinated Universal Time (UTC) values that
17 # are transmitted by almost all time services.
19 # The first column shows an epoch as a number of seconds
20 # since 1900.0 and the second column shows the number of
21 # seconds that must be added to UTC to compute TAI for
22 # any timestamp at or after that epoch. The value on
23 # each line is valid from the indicated initial instant
24 # until the epoch given on the next one or indefinitely
25 # into the future if there is no next line.
26 # (The comment on each line shows the representation of
27 # the corresponding initial epoch in the usual
28 # day-month-year format. The epoch always begins at
29 # 00:00:00 UTC on the indicated day. See Note 5 below.)
33 # 1. Coordinated Universal Time (UTC) is often referred to
34 # as Greenwich Mean Time (GMT). The GMT time scale is no
35 # longer used, and the use of GMT to designate UTC is
38 # 2. The UTC time scale is realized by many national
39 # laboratories and timing centers. Each laboratory
40 # identifies its realization with its name: Thus
41 # UTC(NIST), UTC(USNO), etc. The differences among
42 # these different realizations are typically on the
43 # order of a few nanoseconds (i.e., 0.000 000 00x s)
44 # and can be ignored for many purposes. These differences
45 # are tabulated in Circular T, which is published monthly
46 # by the International Bureau of Weights and Measures
47 # (BIPM). See www.bipm.fr for more information.
49 # 3. The current definition of the relationship between UTC
50 # and TAI dates from 1 January 1972. A number of different
51 # time scales were in use before than epoch, and it can be
52 # quite difficult to compute precise timestamps and time
53 # intervals in those "prehistoric" days. For more information,
56 # The Explanatory Supplement to the Astronomical
59 # Terry Quinn, "The BIPM and the Accurate Measurement
60 # of Time," Proc. of the IEEE, Vol. 79, pp. 894-905,
63 # 4. The insertion of leap seconds into UTC is currently the
64 # responsibility of the International Earth Rotation Service,
65 # which is located at the Paris Observatory:
67 # Central Bureau of IERS
68 # 61, Avenue de l'Observatoire
69 # 75014 Paris, France.
71 # Leap seconds are announced by the IERS in its Bulletin C
73 # See hpiers.obspm.fr or www.iers.org for more details.
75 # All national laboratories and timing centers use the
76 # data from the BIPM and the IERS to construct their
77 # local realizations of UTC.
79 # Although the definition also includes the possibility
80 # of dropping seconds ("negative" leap seconds), this has
81 # never been done and is unlikely to be necessary in the
84 # 5. If your system keeps time as the number of seconds since
85 # some epoch (e.g., NTP timestamps), then the algorithm for
86 # assigning a UTC time stamp to an event that happens during a positive
87 # leap second is not well defined. The official name of that leap
88 # second is 23:59:60, but there is no way of representing that time
90 # Many systems of this type effectively stop the system clock for
91 # one second during the leap second and use a time that is equivalent
92 # to 23:59:59 UTC twice. For these systems, the corresponding TAI
93 # timestamp would be obtained by advancing to the next entry in the
94 # following table when the time equivalent to 23:59:59 UTC
95 # is used for the second time. Thus the leap second which
96 # occurred on 30 June 1972 at 23:59:59 UTC would have TAI
97 # timestamps computed as follows:
100 # 30 June 1972 23:59:59 (2287785599, first time): TAI= UTC + 10 seconds
101 # 30 June 1972 23:59:60 (2287785599,second time): TAI= UTC + 11 seconds
102 # 1 July 1972 00:00:00 (2287785600) TAI= UTC + 11 seconds
105 # If your system realizes the leap second by repeating 00:00:00 UTC twice
106 # (this is possible but not usual), then the advance to the next entry
107 # in the table must occur the second time that a time equivlent to
108 # 00:00:00 UTC is used. Thus, using the same example as above:
111 # 30 June 1972 23:59:59 (2287785599): TAI= UTC + 10 seconds
112 # 30 June 1972 23:59:60 (2287785600, first time): TAI= UTC + 10 seconds
113 # 1 July 1972 00:00:00 (2287785600,second time): TAI= UTC + 11 seconds
116 # in both cases the use of timestamps based on TAI produces a smooth
117 # time scale with no discontinuity in the time interval.
119 # This complexity would not be needed for negative leap seconds (if they
120 # are ever used). The UTC time would skip 23:59:59 and advance from
121 # 23:59:58 to 00:00:00 in that case. The TAI offset would decrease by
122 # 1 second at the same instant. This is a much easier situation to deal
123 # with, since the difficulty of unambiguously representing the epoch
124 # during the leap second does not arise.
126 # Questions or comments to:
128 # Time Service Department
129 # US Naval Observatory
131 # jeffrey.prillaman@usno.navy.mil
133 # Last Update of leap second values: 11 Jan 2016
135 # The following line shows this last update date in NTP timestamp
136 # format. This is the date on which the most recent change to
137 # the leap second data was added to the file. This line can
138 # be identified by the unique pair of characters in the first two
139 # columns as shown below.
143 # The data in this file will be updated periodically as new leap
144 # seconds are announced. In addition to being entered on the line
145 # above, the update time (in NTP format) will be added to the basic
146 # file name leap-seconds to form the name leap-seconds.<NTP TIME>.
147 # In addition, the generic name leap-seconds.list will always point to
148 # the most recent version of the file.
150 # This update procedure will be performed only when a new leap second
153 # The following entry specifies the expiration date of the data
154 # in this file in units of seconds since 1900.0. This expiration date
155 # will be changed at least twice per year whether or not a new leap
156 # second is announced. These semi-annual changes will be made no
157 # later than 1 June and 1 December of each year to indicate what
158 # action (if any) is to be taken on 30 June and 31 December,
159 # respectively. (These are the customary effective dates for new
160 # leap seconds.) This expiration date will be identified by a
161 # unique pair of characters in columns 1 and 2 as shown below.
162 # In the unlikely event that a leap second is announced with an
163 # effective date other than 30 June or 31 December, then this
164 # file will be edited to include that leap second as soon as it is
165 # announced or at least one month before the effective date
166 # (whichever is later).
167 # If an announcement by the IERS specifies that no leap second is
168 # scheduled, then only the expiration date of the file will
169 # be advanced to show that the information in the file is still
170 # current -- the update time stamp, the data and the name of the file
173 # Updated through IERS Bulletin C 51
174 # File expires on: 1 Dec 2016
178 2272060800 10 # 1 Jan 1972
179 2287785600 11 # 1 Jul 1972
180 2303683200 12 # 1 Jan 1973
181 2335219200 13 # 1 Jan 1974
182 2366755200 14 # 1 Jan 1975
183 2398291200 15 # 1 Jan 1976
184 2429913600 16 # 1 Jan 1977
185 2461449600 17 # 1 Jan 1978
186 2492985600 18 # 1 Jan 1979
187 2524521600 19 # 1 Jan 1980
188 2571782400 20 # 1 Jul 1981
189 2603318400 21 # 1 Jul 1982
190 2634854400 22 # 1 Jul 1983
191 2698012800 23 # 1 Jul 1985
192 2776982400 24 # 1 Jan 1988
193 2840140800 25 # 1 Jan 1990
194 2871676800 26 # 1 Jan 1991
195 2918937600 27 # 1 Jul 1992
196 2950473600 28 # 1 Jul 1993
197 2982009600 29 # 1 Jul 1994
198 3029443200 30 # 1 Jan 1996
199 3076704000 31 # 1 Jul 1997
200 3124137600 32 # 1 Jan 1999
201 3345062400 33 # 1 Jan 2006
202 3439756800 34 # 1 Jan 2009
203 3550089600 35 # 1 Jul 2012
204 3644697600 36 # 1 Jul 2015
206 # the following special comment contains the
207 # hash value of the data in this file computed
208 # use the secure hash algorithm as specified
209 # by FIPS 180-1. See the files in ~/sha for
210 # the details of how this hash value is
211 # computed. Note that the hash computation
212 # ignores comments and whitespace characters
213 # in data lines. It includes the NTP values
214 # of both the last modification time and the
215 # expiration time of the file, but not the
216 # white space on those lines.
217 # the hash line is also ignored in the
220 #h 63b4df04 0907d94f 2dadb7a1 684f7767 2a372421