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Original file line number | Diff line number | Diff line change |
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KPL/LSK | ||
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LEAPSECONDS KERNEL FILE | ||
=========================================================================== | ||
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Modifications: | ||
-------------- | ||
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2016, Jul. 14 NJB Modified file to account for the leapsecond that | ||
will occur on December 31, 2016. | ||
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2015, Jan. 5 NJB Modified file to account for the leapsecond that | ||
will occur on June 30, 2015. | ||
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2012, Jan. 5 NJB Modified file to account for the leapsecond that | ||
will occur on June 30, 2012. | ||
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2008, Jul. 7 NJB Modified file to account for the leapsecond that | ||
will occur on December 31, 2008. | ||
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2005, Aug. 3 NJB Modified file to account for the leapsecond that | ||
will occur on December 31, 2005. | ||
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1998, Jul 17 WLT Modified file to account for the leapsecond that | ||
will occur on December 31, 1998. | ||
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1997, Feb 22 WLT Modified file to account for the leapsecond that | ||
will occur on June 30, 1997. | ||
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1995, Dec 14 KSZ Corrected date of last leapsecond from 1-1-95 | ||
to 1-1-96. | ||
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1995, Oct 25 WLT Modified file to account for the leapsecond that | ||
will occur on Dec 31, 1995. | ||
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1994, Jun 16 WLT Modified file to account for the leapsecond on | ||
June 30, 1994. | ||
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1993, Feb. 22 CHA Modified file to account for the leapsecond on | ||
June 30, 1993. | ||
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1992, Mar. 6 HAN Modified file to account for the leapsecond on | ||
June 30, 1992. | ||
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1990, Oct. 8 HAN Modified file to account for the leapsecond on | ||
Dec. 31, 1990. | ||
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Explanation: | ||
------------ | ||
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The contents of this file are used by the routine DELTET to compute the | ||
time difference | ||
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[1] DELTA_ET = ET - UTC | ||
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the increment to be applied to UTC to give ET. | ||
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The difference between UTC and TAI, | ||
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[2] DELTA_AT = TAI - UTC | ||
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is always an integral number of seconds. The value of DELTA_AT was 10 | ||
seconds in January 1972, and increases by one each time a leap second | ||
is declared. Combining [1] and [2] gives | ||
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[3] DELTA_ET = ET - (TAI - DELTA_AT) | ||
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= (ET - TAI) + DELTA_AT | ||
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The difference (ET - TAI) is periodic, and is given by | ||
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[4] ET - TAI = DELTA_T_A + K sin E | ||
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where DELTA_T_A and K are constant, and E is the eccentric anomaly of the | ||
heliocentric orbit of the Earth-Moon barycenter. Equation [4], which ignores | ||
small-period fluctuations, is accurate to about 0.000030 seconds. | ||
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The eccentric anomaly E is given by | ||
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[5] E = M + EB sin M | ||
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where M is the mean anomaly, which in turn is given by | ||
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[6] M = M + M t | ||
0 1 | ||
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where t is the number of ephemeris seconds past J2000. | ||
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Thus, in order to compute DELTA_ET, the following items are necessary. | ||
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DELTA_TA | ||
K | ||
EB | ||
M0 | ||
M1 | ||
DELTA_AT after each leap second. | ||
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The numbers, and the formulation, are taken from the following sources. | ||
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1) Moyer, T.D., Transformation from Proper Time on Earth to | ||
Coordinate Time in Solar System Barycentric Space-Time Frame | ||
of Reference, Parts 1 and 2, Celestial Mechanics 23 (1981), | ||
33-56 and 57-68. | ||
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2) Moyer, T.D., Effects of Conversion to the J2000 Astronomical | ||
Reference System on Algorithms for Computing Time Differences | ||
and Clock Rates, JPL IOM 314.5--942, 1 October 1985. | ||
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The variable names used above are consistent with those used in the | ||
Astronomical Almanac. | ||
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\begindata | ||
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DELTET/DELTA_T_A = 32.184 | ||
DELTET/K = 1.657D-3 | ||
DELTET/EB = 1.671D-2 | ||
DELTET/M = ( 6.239996D0 1.99096871D-7 ) | ||
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DELTET/DELTA_AT = ( 10, @1972-JAN-1 | ||
11, @1972-JUL-1 | ||
12, @1973-JAN-1 | ||
13, @1974-JAN-1 | ||
14, @1975-JAN-1 | ||
15, @1976-JAN-1 | ||
16, @1977-JAN-1 | ||
17, @1978-JAN-1 | ||
18, @1979-JAN-1 | ||
19, @1980-JAN-1 | ||
20, @1981-JUL-1 | ||
21, @1982-JUL-1 | ||
22, @1983-JUL-1 | ||
23, @1985-JUL-1 | ||
24, @1988-JAN-1 | ||
25, @1990-JAN-1 | ||
26, @1991-JAN-1 | ||
27, @1992-JUL-1 | ||
28, @1993-JUL-1 | ||
29, @1994-JUL-1 | ||
30, @1996-JAN-1 | ||
31, @1997-JUL-1 | ||
32, @1999-JAN-1 | ||
33, @2006-JAN-1 | ||
34, @2009-JAN-1 | ||
35, @2012-JUL-1 | ||
36, @2015-JUL-1 | ||
37, @2017-JAN-1 ) | ||
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\begintext | ||
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