source: trunk/MagicSoft/slalib/ecmat.c@ 11169

Last change on this file since 11169 was 731, checked in by tbretz, 24 years ago
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1#include "slalib.h"
2#include "slamac.h"
3void slaEcmat ( double date, double rmat[3][3] )
4/*
5** - - - - - - - - -
6** s l a E c m a t
7** - - - - - - - - -
8**
9** Form the equatorial to ecliptic rotation matrix (IAU 1980 theory).
10**
11** (double precision)
12**
13** Given:
14** date double TDB (loosely ET) as Modified Julian Date
15** (JD-2400000.5)
16** Returned:
17** rmat double[3][3] matrix
18**
19** References:
20** Murray, C.A., Vectorial Astrometry, section 4.3.
21**
22** Note:
23** The matrix is in the sense v[ecl] = rmat * v[equ]; the
24** equator, equinox and ecliptic are mean of date.
25**
26** Called: slaDeuler
27**
28** Defined in slamac.h: DAS2R
29**
30** Last revision: 31 October 1993
31**
32** Copyright P.T.Wallace. All rights reserved.
33*/
34{
35 double t, eps0;
36
37/* Interval between basic epoch J2000.0 and current epoch (JC) */
38 t = ( date - 51544.5 ) / 36525.0;
39
40/* Mean obliquity */
41 eps0 = DAS2R *
42 ( 84381.448 + ( -46.8150 + ( -0.00059 + 0.001813 * t ) * t ) * t );
43
44/* Matrix */
45 slaDeuler ( "X", eps0, 0.0, 0.0, rmat );
46}
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