1# ATOMIC TIME 2# Coordinated Universal Time (UTC) is the reference time scale derived 3# from The "Temps Atomique International" (TAI) calculated by the Bureau 4# International des Poids et Mesures (BIPM) using a worldwide network of atomic 5# clocks. UTC differs from TAI by an integer number of seconds; it is the basis 6# of all activities in the world. 7# 8# 9# ASTRONOMICAL TIME (UT1) is the time scale based on the rate of rotation of the earth. 10# It is now mainly derived from Very Long Baseline Interferometry (VLBI). The various 11# irregular fluctuations progressively detected in the rotation rate of the Earth led 12# in 1972 to the replacement of UT1 by UTC as the reference time scale. 13# 14# 15# LEAP SECOND 16# Atomic clocks are more stable than the rate of the earth's rotation since the latter 17# undergoes a full range of geophysical perturbations at various time scales: lunisolar 18# and core-mantle torques, atmospheric and oceanic effects, etc. 19# Leap seconds are needed to keep the two time scales in agreement, i.e. UT1-UTC smaller 20# than 0.9 seconds. Therefore, when necessary a "leap second" is applied to UTC. 21# Since the adoption of this system in 1972 it has been necessary to add a number of seconds to UTC, 22# firstly due to the initial choice of the value of the second (1/86400 mean solar day of 23# the year 1820) and secondly to the general slowing down of the Earth's rotation. It is 24# theoretically possible to have a negative leap second (a second removed from UTC), but so far, 25# all leap seconds have been positive (a second has been added to UTC). Based on what we know about 26# the earth's rotation, it is unlikely that we will ever have a negative leap second. 27# 28# 29# HISTORY 30# The first leap second was added on June 30, 1972. Until the year 2000, it was necessary in average to add a 31# leap second at a rate of 1 to 2 years. Since the year 2000 leap seconds are introduced with an 32# average interval of 3 to 4 years due to the acceleration of the Earth's rotation speed. 33# 34# 35# RESPONSIBILITY OF THE DECISION TO INTRODUCE A LEAP SECOND IN UTC 36# The decision to introduce a leap second in UTC is the responsibility of the Earth Orientation Center of 37# the International Earth Rotation and reference System Service (IERS). This center is located at Paris 38# Observatory. According to international agreements, leap seconds should be scheduled only for certain dates: 39# first preference is given to the end of December and June, and second preference at the end of March 40# and September. Since the introduction of leap seconds in 1972, only dates in June and December were used. 41# 42# Questions or comments to: 43# Christian Bizouard: christian.bizouard@obspm.fr 44# Earth orientation Center of the IERS 45# Paris Observatory, France 46# 47# 48# 49# COPYRIGHT STATUS OF THIS FILE 50# This file is in the public domain. 51# 52# 53# VALIDITY OF THE FILE 54# It is important to express the validity of the file. These next two dates are 55# given in units of seconds since 1900.0. 56# 57# 1) Last update of the file. 58# 59# Updated through IERS Bulletin C (https://hpiers.obspm.fr/iers/bul/bulc/bulletinc.dat) 60# 61# The following line shows the last update of this file in NTP timestamp: 62# 63#$ 3929093563 64# 65# 2) Expiration date of the file given on a semi-annual basis: last June or last December 66# 67# File expires on 28 June 2025 68# 69# Expire date in NTP timestamp: 70# 71#@ 3960057600 72# 73# 74# LIST OF LEAP SECONDS 75# NTP timestamp (X parameter) is the number of seconds since 1900.0 76# 77# MJD: The Modified Julian Day number. MJD = X/86400 + 15020 78# 79# DTAI: The difference DTAI= TAI-UTC in units of seconds 80# It is the quantity to add to UTC to get the time in TAI 81# 82# Day Month Year : epoch in clear 83# 84#NTP Time DTAI Day Month Year 85# 862272060800 10 # 1 Jan 1972 872287785600 11 # 1 Jul 1972 882303683200 12 # 1 Jan 1973 892335219200 13 # 1 Jan 1974 902366755200 14 # 1 Jan 1975 912398291200 15 # 1 Jan 1976 922429913600 16 # 1 Jan 1977 932461449600 17 # 1 Jan 1978 942492985600 18 # 1 Jan 1979 952524521600 19 # 1 Jan 1980 962571782400 20 # 1 Jul 1981 972603318400 21 # 1 Jul 1982 982634854400 22 # 1 Jul 1983 992698012800 23 # 1 Jul 1985 1002776982400 24 # 1 Jan 1988 1012840140800 25 # 1 Jan 1990 1022871676800 26 # 1 Jan 1991 1032918937600 27 # 1 Jul 1992 1042950473600 28 # 1 Jul 1993 1052982009600 29 # 1 Jul 1994 1063029443200 30 # 1 Jan 1996 1073076704000 31 # 1 Jul 1997 1083124137600 32 # 1 Jan 1999 1093345062400 33 # 1 Jan 2006 1103439756800 34 # 1 Jan 2009 1113550089600 35 # 1 Jul 2012 1123644697600 36 # 1 Jul 2015 1133692217600 37 # 1 Jan 2017 114# 115# A hash code has been generated to be able to verify the integrity 116# of this file. For more information about using this hash code, 117# please see the readme file in the 'source' directory : 118# https://hpiers.obspm.fr/iers/bul/bulc/ntp/sources/README 119# 120#h be738595 57b0cf1b b0218343 fb77062f 5a775e7 121