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Diffstat (limited to 'ast/erfa/eqeq94.c')
| -rw-r--r-- | ast/erfa/eqeq94.c | 141 |
1 files changed, 141 insertions, 0 deletions
diff --git a/ast/erfa/eqeq94.c b/ast/erfa/eqeq94.c new file mode 100644 index 0000000..00076b1 --- /dev/null +++ b/ast/erfa/eqeq94.c @@ -0,0 +1,141 @@ +#include "erfa.h" + +double eraEqeq94(double date1, double date2) +/* +** - - - - - - - - - - +** e r a E q e q 9 4 +** - - - - - - - - - - +** +** Equation of the equinoxes, IAU 1994 model. +** +** Given: +** date1,date2 double TDB date (Note 1) +** +** Returned (function value): +** double equation of the equinoxes (Note 2) +** +** Notes: +** +** 1) The 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 result, which is in radians, operates in the following sense: +** +** Greenwich apparent ST = GMST + equation of the equinoxes +** +** Called: +** eraAnpm normalize angle into range +/- pi +** eraNut80 nutation, IAU 1980 +** eraObl80 mean obliquity, IAU 1980 +** +** References: +** +** IAU Resolution C7, Recommendation 3 (1994). +** +** Capitaine, N. & Gontier, A.-M., 1993, Astron. Astrophys., 275, +** 645-650. +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ + double t, om, dpsi, deps, eps0, ee; + + +/* Interval between fundamental epoch J2000.0 and given date (JC). */ + t = ((date1 - ERFA_DJ00) + date2) / ERFA_DJC; + +/* Longitude of the mean ascending node of the lunar orbit on the */ +/* ecliptic, measured from the mean equinox of date. */ + om = eraAnpm((450160.280 + (-482890.539 + + (7.455 + 0.008 * t) * t) * t) * ERFA_DAS2R + + fmod(-5.0 * t, 1.0) * ERFA_D2PI); + +/* Nutation components and mean obliquity. */ + eraNut80(date1, date2, &dpsi, &deps); + eps0 = eraObl80(date1, date2); + +/* Equation of the equinoxes. */ + ee = dpsi*cos(eps0) + ERFA_DAS2R*(0.00264*sin(om) + 0.000063*sin(om+om)); + + return ee; + +} +/*---------------------------------------------------------------------- +** +** +** Copyright (C) 2013-2016, 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. +** +*/ |