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on this file since 9483 was 731, checked in by tbretz, 24 years ago |
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1 | #include "slalib.h"
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2 | #include "slamac.h"
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3 | void slaEcmat ( double date, double rmat[3][3] )
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4 | /*
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5 | ** - - - - - - - - -
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6 | ** s l a E c m a t
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7 | ** - - - - - - - - -
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8 | **
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9 | ** Form the equatorial to ecliptic rotation matrix (IAU 1980 theory).
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10 | **
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11 | ** (double precision)
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12 | **
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13 | ** Given:
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14 | ** date double TDB (loosely ET) as Modified Julian Date
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15 | ** (JD-2400000.5)
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16 | ** Returned:
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17 | ** rmat double[3][3] matrix
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18 | **
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19 | ** References:
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20 | ** Murray, C.A., Vectorial Astrometry, section 4.3.
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21 | **
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22 | ** Note:
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23 | ** The matrix is in the sense v[ecl] = rmat * v[equ]; the
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24 | ** equator, equinox and ecliptic are mean of date.
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25 | **
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26 | ** Called: slaDeuler
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27 | **
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28 | ** Defined in slamac.h: DAS2R
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29 | **
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30 | ** Last revision: 31 October 1993
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31 | **
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32 | ** Copyright P.T.Wallace. All rights reserved.
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33 | */
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34 | {
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35 | double t, eps0;
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36 |
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37 | /* Interval between basic epoch J2000.0 and current epoch (JC) */
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38 | t = ( date - 51544.5 ) / 36525.0;
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39 |
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40 | /* Mean obliquity */
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41 | eps0 = DAS2R *
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42 | ( 84381.448 + ( -46.8150 + ( -0.00059 + 0.001813 * t ) * t ) * t );
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43 |
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44 | /* Matrix */
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45 | slaDeuler ( "X", eps0, 0.0, 0.0, rmat );
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46 | }
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