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Diffstat (limited to 'ast/erfa/eect00.c')
| -rw-r--r-- | ast/erfa/eect00.c | 291 |
1 files changed, 291 insertions, 0 deletions
diff --git a/ast/erfa/eect00.c b/ast/erfa/eect00.c new file mode 100644 index 0000000..d2af497 --- /dev/null +++ b/ast/erfa/eect00.c @@ -0,0 +1,291 @@ +#include "erfa.h" + +double eraEect00(double date1, double date2) +/* +** - - - - - - - - - - +** e r a E e c t 0 0 +** - - - - - - - - - - +** +** Equation of the equinoxes complementary terms, consistent with +** IAU 2000 resolutions. +** +** Given: +** date1,date2 double TT as a 2-part Julian Date (Note 1) +** +** Returned (function value): +** double complementary terms (Note 2) +** +** Notes: +** +** 1) The TT date date1+date2 is a Julian Date, apportioned in any +** convenient way between the two arguments. For example, +** JD(TT)=2450123.7 could be expressed in any of these ways, +** among others: +** +** date1 date2 +** +** 2450123.7 0.0 (JD method) +** 2451545.0 -1421.3 (J2000 method) +** 2400000.5 50123.2 (MJD method) +** 2450123.5 0.2 (date & time method) +** +** The JD method is the most natural and convenient to use in +** cases where the loss of several decimal digits of resolution +** is acceptable. The J2000 method is best matched to the way +** the argument is handled internally and will deliver the +** optimum resolution. The MJD method and the date & time methods +** are both good compromises between resolution and convenience. +** +** 2) The "complementary terms" are part of the equation of the +** equinoxes (EE), classically the difference between apparent and +** mean Sidereal Time: +** +** GAST = GMST + EE +** +** with: +** +** EE = dpsi * cos(eps) +** +** where dpsi is the nutation in longitude and eps is the obliquity +** of date. However, if the rotation of the Earth were constant in +** an inertial frame the classical formulation would lead to +** apparent irregularities in the UT1 timescale traceable to side- +** effects of precession-nutation. In order to eliminate these +** effects from UT1, "complementary terms" were introduced in 1994 +** (IAU, 1994) and took effect from 1997 (Capitaine and Gontier, +** 1993): +** +** GAST = GMST + CT + EE +** +** By convention, the complementary terms are included as part of +** the equation of the equinoxes rather than as part of the mean +** Sidereal Time. This slightly compromises the "geometrical" +** interpretation of mean sidereal time but is otherwise +** inconsequential. +** +** The present function computes CT in the above expression, +** compatible with IAU 2000 resolutions (Capitaine et al., 2002, and +** IERS Conventions 2003). +** +** Called: +** eraFal03 mean anomaly of the Moon +** eraFalp03 mean anomaly of the Sun +** eraFaf03 mean argument of the latitude of the Moon +** eraFad03 mean elongation of the Moon from the Sun +** eraFaom03 mean longitude of the Moon's ascending node +** eraFave03 mean longitude of Venus +** eraFae03 mean longitude of Earth +** eraFapa03 general accumulated precession in longitude +** +** References: +** +** Capitaine, N. & Gontier, A.-M., Astron. Astrophys., 275, +** 645-650 (1993) +** +** Capitaine, N., Wallace, P.T. and McCarthy, D.D., "Expressions to +** implement the IAU 2000 definition of UT1", Astronomy & +** Astrophysics, 406, 1135-1149 (2003) +** +** IAU Resolution C7, Recommendation 3 (1994) +** +** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003), +** IERS Technical Note No. 32, BKG (2004) +** +** Copyright (C) 2013-2014, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ +/* Time since J2000.0, in Julian centuries */ + double t; + +/* Miscellaneous */ + int i, j; + double a, s0, s1; + +/* Fundamental arguments */ + double fa[14]; + +/* Returned value. */ + double eect; + +/* ----------------------------------------- */ +/* The series for the EE complementary terms */ +/* ----------------------------------------- */ + + typedef struct { + int nfa[8]; /* coefficients of l,l',F,D,Om,LVe,LE,pA */ + double s, c; /* sine and cosine coefficients */ + } TERM; + +/* Terms of order t^0 */ + static const TERM e0[] = { + + /* 1-10 */ + {{ 0, 0, 0, 0, 1, 0, 0, 0}, 2640.96e-6, -0.39e-6 }, + {{ 0, 0, 0, 0, 2, 0, 0, 0}, 63.52e-6, -0.02e-6 }, + {{ 0, 0, 2, -2, 3, 0, 0, 0}, 11.75e-6, 0.01e-6 }, + {{ 0, 0, 2, -2, 1, 0, 0, 0}, 11.21e-6, 0.01e-6 }, + {{ 0, 0, 2, -2, 2, 0, 0, 0}, -4.55e-6, 0.00e-6 }, + {{ 0, 0, 2, 0, 3, 0, 0, 0}, 2.02e-6, 0.00e-6 }, + {{ 0, 0, 2, 0, 1, 0, 0, 0}, 1.98e-6, 0.00e-6 }, + {{ 0, 0, 0, 0, 3, 0, 0, 0}, -1.72e-6, 0.00e-6 }, + {{ 0, 1, 0, 0, 1, 0, 0, 0}, -1.41e-6, -0.01e-6 }, + {{ 0, 1, 0, 0, -1, 0, 0, 0}, -1.26e-6, -0.01e-6 }, + + /* 11-20 */ + {{ 1, 0, 0, 0, -1, 0, 0, 0}, -0.63e-6, 0.00e-6 }, + {{ 1, 0, 0, 0, 1, 0, 0, 0}, -0.63e-6, 0.00e-6 }, + {{ 0, 1, 2, -2, 3, 0, 0, 0}, 0.46e-6, 0.00e-6 }, + {{ 0, 1, 2, -2, 1, 0, 0, 0}, 0.45e-6, 0.00e-6 }, + {{ 0, 0, 4, -4, 4, 0, 0, 0}, 0.36e-6, 0.00e-6 }, + {{ 0, 0, 1, -1, 1, -8, 12, 0}, -0.24e-6, -0.12e-6 }, + {{ 0, 0, 2, 0, 0, 0, 0, 0}, 0.32e-6, 0.00e-6 }, + {{ 0, 0, 2, 0, 2, 0, 0, 0}, 0.28e-6, 0.00e-6 }, + {{ 1, 0, 2, 0, 3, 0, 0, 0}, 0.27e-6, 0.00e-6 }, + {{ 1, 0, 2, 0, 1, 0, 0, 0}, 0.26e-6, 0.00e-6 }, + + /* 21-30 */ + {{ 0, 0, 2, -2, 0, 0, 0, 0}, -0.21e-6, 0.00e-6 }, + {{ 0, 1, -2, 2, -3, 0, 0, 0}, 0.19e-6, 0.00e-6 }, + {{ 0, 1, -2, 2, -1, 0, 0, 0}, 0.18e-6, 0.00e-6 }, + {{ 0, 0, 0, 0, 0, 8,-13, -1}, -0.10e-6, 0.05e-6 }, + {{ 0, 0, 0, 2, 0, 0, 0, 0}, 0.15e-6, 0.00e-6 }, + {{ 2, 0, -2, 0, -1, 0, 0, 0}, -0.14e-6, 0.00e-6 }, + {{ 1, 0, 0, -2, 1, 0, 0, 0}, 0.14e-6, 0.00e-6 }, + {{ 0, 1, 2, -2, 2, 0, 0, 0}, -0.14e-6, 0.00e-6 }, + {{ 1, 0, 0, -2, -1, 0, 0, 0}, 0.14e-6, 0.00e-6 }, + {{ 0, 0, 4, -2, 4, 0, 0, 0}, 0.13e-6, 0.00e-6 }, + + /* 31-33 */ + {{ 0, 0, 2, -2, 4, 0, 0, 0}, -0.11e-6, 0.00e-6 }, + {{ 1, 0, -2, 0, -3, 0, 0, 0}, 0.11e-6, 0.00e-6 }, + {{ 1, 0, -2, 0, -1, 0, 0, 0}, 0.11e-6, 0.00e-6 } + }; + +/* Terms of order t^1 */ + static const TERM e1[] = { + {{ 0, 0, 0, 0, 1, 0, 0, 0}, -0.87e-6, 0.00e-6 } + }; + +/* Number of terms in the series */ + const int NE0 = (int) (sizeof e0 / sizeof (TERM)); + const int NE1 = (int) (sizeof e1 / sizeof (TERM)); + +/*--------------------------------------------------------------------*/ + +/* Interval between fundamental epoch J2000.0 and current date (JC). */ + t = ((date1 - ERFA_DJ00) + date2) / ERFA_DJC; + +/* Fundamental Arguments (from IERS Conventions 2003) */ + +/* Mean anomaly of the Moon. */ + fa[0] = eraFal03(t); + +/* Mean anomaly of the Sun. */ + fa[1] = eraFalp03(t); + +/* Mean longitude of the Moon minus that of the ascending node. */ + fa[2] = eraFaf03(t); + +/* Mean elongation of the Moon from the Sun. */ + fa[3] = eraFad03(t); + +/* Mean longitude of the ascending node of the Moon. */ + fa[4] = eraFaom03(t); + +/* Mean longitude of Venus. */ + fa[5] = eraFave03(t); + +/* Mean longitude of Earth. */ + fa[6] = eraFae03(t); + +/* General precession in longitude. */ + fa[7] = eraFapa03(t); + +/* Evaluate the EE complementary terms. */ + s0 = 0.0; + s1 = 0.0; + + for (i = NE0-1; i >= 0; i--) { + a = 0.0; + for (j = 0; j < 8; j++) { + a += (double)(e0[i].nfa[j]) * fa[j]; + } + s0 += e0[i].s * sin(a) + e0[i].c * cos(a); + } + + for (i = NE1-1; i >= 0; i--) { + a = 0.0; + for (j = 0; j < 8; j++) { + a += (double)(e1[i].nfa[j]) * fa[j]; + } + s1 += e1[i].s * sin(a) + e1[i].c * cos(a); + } + + eect = (s0 + s1 * t ) * ERFA_DAS2R; + + return eect; + +} +/*---------------------------------------------------------------------- +** +** +** Copyright (C) 2013-2014, NumFOCUS Foundation. +** All rights reserved. +** +** This library is derived, with permission, from the International +** Astronomical Union's "Standards of Fundamental Astronomy" library, +** available from http://www.iausofa.org. +** +** The ERFA version is intended to retain identical functionality to +** the SOFA library, but made distinct through different function and +** file names, as set out in the SOFA license conditions. The SOFA +** original has a role as a reference standard for the IAU and IERS, +** and consequently redistribution is permitted only in its unaltered +** state. The ERFA version is not subject to this restriction and +** therefore can be included in distributions which do not support the +** concept of "read only" software. +** +** Although the intent is to replicate the SOFA API (other than +** replacement of prefix names) and results (with the exception of +** bugs; any that are discovered will be fixed), SOFA is not +** responsible for any errors found in this version of the library. +** +** If you wish to acknowledge the SOFA heritage, please acknowledge +** that you are using a library derived from SOFA, rather than SOFA +** itself. +** +** +** TERMS AND CONDITIONS +** +** Redistribution and use in source and binary forms, with or without +** modification, are permitted provided that the following conditions +** are met: +** +** 1 Redistributions of source code must retain the above copyright +** notice, this list of conditions and the following disclaimer. +** +** 2 Redistributions in binary form must reproduce the above copyright +** notice, this list of conditions and the following disclaimer in +** the documentation and/or other materials provided with the +** distribution. +** +** 3 Neither the name of the Standards Of Fundamental Astronomy Board, +** the International Astronomical Union nor the names of its +** contributors may be used to endorse or promote products derived +** from this software without specific prior written permission. +** +** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS +** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT +** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS +** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE +** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, +** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, +** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; +** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER +** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN +** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE +** POSSIBILITY OF SUCH DAMAGE. +** +*/ |