120 lines
4.8 KiB
Plaintext
120 lines
4.8 KiB
Plaintext
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#
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# $FreeBSD$
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#
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# ATOMIC TIME.
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# The Coordinated Universal Time (UTC) is the reference time scale derived
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# from The "Temps Atomique International" (TAI) calculated by the Bureau
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# International des Poids et Mesures (BIPM) using a worldwide network of atomic
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# clocks. UTC differs from TAI by an integer number of seconds; it is the basis
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# of all activities in the world.
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#
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#
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# ASTRONOMICAL TIME (UT1) is the time scale based on the rate of rotation of the earth.
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# It is now mainly derived from Very Long Baseline Interferometry (VLBI). The various
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# irregular fluctuations progressively detected in the rotation rate of the Earth lead
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# in 1972 to the replacement of UT1 by UTC as the reference time scale.
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#
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#
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# LEAP SECOND
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# Atomic clocks are more stable than the rate of the earth rotatiob since the later
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# undergoes a full range of geophysical perturbations at various time scales (lunisolar
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# and core-mantle torques,atmospheric and oceanic effetcs, ...)
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# Leap seconds are needed to keep the two time scales in agreement, i.e. UT1-UTC smaller
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# than 0.9 second. So, when necessary a "leap second" is introduced in UTC.
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# Since the adoption of this system in 1972 it has been necessary to add 26 seconds to UTC,
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# firstly due to the initial choice of the value of the second (1/86400 mean solar day of
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# the year 1820) and secondly to the general slowing down of the Earth's rotation. It is
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# theorically possible to have a negative leap second (a second removed from UTC), but so far,
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# all leap seconds have been positive (a second has been added to UTC). Based on what we know about the earth's rotation,
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# it is unlikely that we will ever have a negative leap second.
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#
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#
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# HISTORY
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# The first leap second was added on June 30, 1972. Until 2000, it was necessary in average to add a leap second at a rate
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# of 1 to 2 years. Since 2000, due to the fact that the earth rate of rotation is accelerating, leap seconds are introduced
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# with an average frequency of 3 to 4 years.
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#
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#
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# RESPONSABILITY OF THE DECISION TO INTRODUCE A LEAP SECOND IN UTC
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# The decision to introduce a leap second in UTC is the responsibility of the Earth Orientation Center of
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# the International Earth Rotation and reference System Service (IERS). This center is located at Paris
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# Observatory. According to international agreements, leap second date have to occur at fixed date :
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# first preference is given to the end of December and June, and second preference at the end of March
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# and September. Since the system was introduced in 1972, only dates in June and December were used.
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#
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# Questions or comments to:
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# Daniel Gambis, daniel.gambis@obspm.fr
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# Christian Bizouard: christian.bizouard@obspm.fr
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# Earth orientation Center of the IERS
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# Paris Observatory, France
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#
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#
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#
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# VALIDITY OF THE FILE
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# It is important to express the validity of the file. These next two dates are
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# given in units of seconds since 1900.0.
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#
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# 1) Last update of the file.
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#
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# Updated through IERS Bulletin C (ftp://hpiers.obspm.fr/iers/bul/bulc/bulletinc.dat)
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#
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# The following line shows the last update of this file in NTP timestamp:
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#
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#$ 3645216000
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#
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# 2) Expiration date of the file given on a semi-annual basis: last June or last December
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#
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# File expires on 28 December 2015
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#
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# Expire date in NTP timestamp:
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#
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#@ 3660249600
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#
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#
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# LIST OF LEAP SECONDS
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# NTP timestamp (X parameter) is the number of seconds since 1900.0
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#
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# MJD: The Modified Julian Day number. MJD = X/86400 + 15020
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#
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# DTAI: The difference DTAI= TAI-UTC in units of seconds
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# It is the quantity to add to UTC to get the time in TAI
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#
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# Day Month Year : epoch in clear
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#
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#NTP Time DTAI Day Month Year
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#
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2272060800 10 # 1 Jan 1972
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2287785600 11 # 1 Jul 1972
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2303683200 12 # 1 Jan 1973
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2335219200 13 # 1 Jan 1974
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2366755200 14 # 1 Jan 1975
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2398291200 15 # 1 Jan 1976
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2429913600 16 # 1 Jan 1977
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2461449600 17 # 1 Jan 1978
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2492985600 18 # 1 Jan 1979
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2524521600 19 # 1 Jan 1980
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2571782400 20 # 1 Jul 1981
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2603318400 21 # 1 Jul 1982
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2634854400 22 # 1 Jul 1983
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2698012800 23 # 1 Jul 1985
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2776982400 24 # 1 Jan 1988
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2840140800 25 # 1 Jan 1990
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2871676800 26 # 1 Jan 1991
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2918937600 27 # 1 Jul 1992
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2950473600 28 # 1 Jul 1993
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2982009600 29 # 1 Jul 1994
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3029443200 30 # 1 Jan 1996
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3076704000 31 # 1 Jul 1997
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3124137600 32 # 1 Jan 1999
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3345062400 33 # 1 Jan 2006
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3439756800 34 # 1 Jan 2009
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3550089600 35 # 1 Jul 2012
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3644697600 36 # 1 Jul 2015
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#
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# In order to verify the integrity of this file, a hash code
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# has been generated. For more information how to use
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# this hash code, please consult the README file under the
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# 'sha' repertory.
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#
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#h 620ba8af 37900668 95ac09ba d77640f9 6fd75493
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