xref: /freebsd/contrib/tzdata/leapseconds (revision 62cfcf62f627e5093fb37026a6d8c98e4d2ef04c)
1# Allowance for leap seconds added to each time zone file.
2
3# This file is in the public domain.
4
5# This file is generated automatically from the data in the public-domain
6# NIST format leap-seconds.list file, which can be copied from
7# <ftp://ftp.nist.gov/pub/time/leap-seconds.list>
8# or <ftp://ftp.boulder.nist.gov/pub/time/leap-seconds.list>.
9# For more about leap-seconds.list, please see
10# The NTP Timescale and Leap Seconds
11# <https://www.eecis.udel.edu/~mills/leap.html>.
12
13# The rules for leap seconds are specified in Annex 1 (Time scales) of:
14# Standard-frequency and time-signal emissions.
15# International Telecommunication Union - Radiocommunication Sector
16# (ITU-R) Recommendation TF.460-6 (02/2002)
17# <https://www.itu.int/rec/R-REC-TF.460-6-200202-I/>.
18# The International Earth Rotation and Reference Systems Service (IERS)
19# periodically uses leap seconds to keep UTC to within 0.9 s of UT1
20# (a proxy for Earth's angle in space as measured by astronomers)
21# and publishes leap second data in a copyrighted file
22# <https://hpiers.obspm.fr/iers/bul/bulc/Leap_Second.dat>.
23# See: Levine J. Coordinated Universal Time and the leap second.
24# URSI Radio Sci Bull. 2016;89(4):30-6. doi:10.23919/URSIRSB.2016.7909995
25# <https://ieeexplore.ieee.org/document/7909995>.
26
27# There were no leap seconds before 1972, as no official mechanism
28# accounted for the discrepancy between atomic time (TAI) and the earth's
29# rotation.  The first ("1 Jan 1972") data line in leap-seconds.list
30# does not denote a leap second; it denotes the start of the current definition
31# of UTC.
32
33# All leap-seconds are Stationary (S) at the given UTC time.
34# The correction (+ or -) is made at the given time, so in the unlikely
35# event of a negative leap second, a line would look like this:
36# Leap	YEAR	MON	DAY	23:59:59	-	S
37# Typical lines look like this:
38# Leap	YEAR	MON	DAY	23:59:60	+	S
39Leap	1972	Jun	30	23:59:60	+	S
40Leap	1972	Dec	31	23:59:60	+	S
41Leap	1973	Dec	31	23:59:60	+	S
42Leap	1974	Dec	31	23:59:60	+	S
43Leap	1975	Dec	31	23:59:60	+	S
44Leap	1976	Dec	31	23:59:60	+	S
45Leap	1977	Dec	31	23:59:60	+	S
46Leap	1978	Dec	31	23:59:60	+	S
47Leap	1979	Dec	31	23:59:60	+	S
48Leap	1981	Jun	30	23:59:60	+	S
49Leap	1982	Jun	30	23:59:60	+	S
50Leap	1983	Jun	30	23:59:60	+	S
51Leap	1985	Jun	30	23:59:60	+	S
52Leap	1987	Dec	31	23:59:60	+	S
53Leap	1989	Dec	31	23:59:60	+	S
54Leap	1990	Dec	31	23:59:60	+	S
55Leap	1992	Jun	30	23:59:60	+	S
56Leap	1993	Jun	30	23:59:60	+	S
57Leap	1994	Jun	30	23:59:60	+	S
58Leap	1995	Dec	31	23:59:60	+	S
59Leap	1997	Jun	30	23:59:60	+	S
60Leap	1998	Dec	31	23:59:60	+	S
61Leap	2005	Dec	31	23:59:60	+	S
62Leap	2008	Dec	31	23:59:60	+	S
63Leap	2012	Jun	30	23:59:60	+	S
64Leap	2015	Jun	30	23:59:60	+	S
65Leap	2016	Dec	31	23:59:60	+	S
66
67# UTC timestamp when this leap second list expires.
68# Any additional leap seconds will come after this.
69# This Expires line is commented out for now,
70# so that pre-2020a zic implementations do not reject this file.
71#Expires 2020	Dec	28	00:00:00
72
73# POSIX timestamps for the data in this file:
74#updated 1467936000 (2016-07-08 00:00:00 UTC)
75#expires 1609113600 (2020-12-28 00:00:00 UTC)
76
77#	Updated through IERS Bulletin C59
78#	File expires on:  28 December 2020
79