xref: /freebsd/contrib/tzdata/leapseconds (revision 5f757f3ff9144b609b3c433dfd370cc6bdc191ad)
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/IERS format leap-seconds.list file, which can be copied from
7# <https://hpiers.obspm.fr/iers/bul/bulc/ntp/leap-seconds.list>
8# or, in a variant with different comments, from
9# <ftp://ftp.boulder.nist.gov/pub/time/leap-seconds.list>.
10# For more about leap-seconds.list, please see
11# The NTP Timescale and Leap Seconds
12# <https://www.eecis.udel.edu/~mills/leap.html>.
13
14# The rules for leap seconds are specified in Annex 1 (Time scales) of:
15# Standard-frequency and time-signal emissions.
16# International Telecommunication Union - Radiocommunication Sector
17# (ITU-R) Recommendation TF.460-6 (02/2002)
18# <https://www.itu.int/rec/R-REC-TF.460-6-200202-I/>.
19# The International Earth Rotation and Reference Systems Service (IERS)
20# periodically uses leap seconds to keep UTC to within 0.9 s of UT1
21# (a proxy for Earth's angle in space as measured by astronomers)
22# and publishes leap second data in a copyrighted file
23# <https://hpiers.obspm.fr/iers/bul/bulc/Leap_Second.dat>.
24# See: Levine J. Coordinated Universal Time and the leap second.
25# URSI Radio Sci Bull. 2016;89(4):30-6. doi:10.23919/URSIRSB.2016.7909995
26# <https://ieeexplore.ieee.org/document/7909995>.
27
28# There were no leap seconds before 1972, as no official mechanism
29# accounted for the discrepancy between atomic time (TAI) and the earth's
30# rotation.  The first ("1 Jan 1972") data line in leap-seconds.list
31# does not denote a leap second; it denotes the start of the current definition
32# of UTC.
33
34# All leap-seconds are Stationary (S) at the given UTC time.
35# The correction (+ or -) is made at the given time, so in the unlikely
36# event of a negative leap second, a line would look like this:
37# Leap	YEAR	MON	DAY	23:59:59	-	S
38# Typical lines look like this:
39# Leap	YEAR	MON	DAY	23:59:60	+	S
40Leap	1972	Jun	30	23:59:60	+	S
41Leap	1972	Dec	31	23:59:60	+	S
42Leap	1973	Dec	31	23:59:60	+	S
43Leap	1974	Dec	31	23:59:60	+	S
44Leap	1975	Dec	31	23:59:60	+	S
45Leap	1976	Dec	31	23:59:60	+	S
46Leap	1977	Dec	31	23:59:60	+	S
47Leap	1978	Dec	31	23:59:60	+	S
48Leap	1979	Dec	31	23:59:60	+	S
49Leap	1981	Jun	30	23:59:60	+	S
50Leap	1982	Jun	30	23:59:60	+	S
51Leap	1983	Jun	30	23:59:60	+	S
52Leap	1985	Jun	30	23:59:60	+	S
53Leap	1987	Dec	31	23:59:60	+	S
54Leap	1989	Dec	31	23:59:60	+	S
55Leap	1990	Dec	31	23:59:60	+	S
56Leap	1992	Jun	30	23:59:60	+	S
57Leap	1993	Jun	30	23:59:60	+	S
58Leap	1994	Jun	30	23:59:60	+	S
59Leap	1995	Dec	31	23:59:60	+	S
60Leap	1997	Jun	30	23:59:60	+	S
61Leap	1998	Dec	31	23:59:60	+	S
62Leap	2005	Dec	31	23:59:60	+	S
63Leap	2008	Dec	31	23:59:60	+	S
64Leap	2012	Jun	30	23:59:60	+	S
65Leap	2015	Jun	30	23:59:60	+	S
66Leap	2016	Dec	31	23:59:60	+	S
67
68# UTC timestamp when this leap second list expires.
69# Any additional leap seconds will come after this.
70# This Expires line is commented out for now,
71# so that pre-2020a zic implementations do not reject this file.
72#Expires 2024	Dec	28	00:00:00
73
74# POSIX timestamps for the data in this file:
75#updated 1704708379 (2024-01-08 10:06:19 UTC)
76#expires 1735344000 (2024-12-28 00:00:00 UTC)
77
78#	Updated through IERS Bulletin C (https://hpiers.obspm.fr/iers/bul/bulc/bulletinc.dat)
79#	File expires on 28 December 2024
80