| 1 | #include "slalib.h"
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| 2 | #include "slamac.h"
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| 3 | void slaRdplan ( double date, int np, double elong, double phi,
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| 4 | double *ra, double *dec, double *diam )
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| 5 | /*
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| 6 | ** - - - - - - - - - -
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| 7 | ** s l a R d p l a n
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| 8 | ** - - - - - - - - - -
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| 9 | **
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| 10 | ** Approximate topocentric apparent RA,Dec of a planet, and its
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| 11 | ** angular diameter.
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| 12 | **
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| 13 | ** Given:
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| 14 | ** date double MJD of observation (JD - 2400000.5)
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| 15 | ** np int planet: 1 = Mercury
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| 16 | ** 2 = Venus
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| 17 | ** 3 = Moon
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| 18 | ** 4 = Mars
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| 19 | ** 5 = Jupiter
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| 20 | ** 6 = Saturn
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| 21 | ** 7 = Uranus
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| 22 | ** 8 = Neptune
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| 23 | ** 9 = Pluto
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| 24 | ** else = Sun
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| 25 | ** elong,phi double observer's east longitude and geodetic
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| 26 | ** latitude (radians)
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| 27 | **
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| 28 | ** Returned:
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| 29 | ** ra,dec double RA, Dec (topocentric apparent, radians)
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| 30 | ** diam double angular diameter (equatorial, radians)
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| 31 | **
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| 32 | ** Notes:
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| 33 | **
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| 34 | ** 1 The date is in a dynamical timescale (TDB, formerly ET) and is
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| 35 | ** in the form of a Modified Julian Date (JD-2400000.5). For all
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| 36 | ** practical purposes, TT can be used instead of TDB, and for many
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| 37 | ** applications UT will do (except for the Moon).
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| 38 | **
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| 39 | ** 2 The longitude and latitude allow correction for geocentric
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| 40 | ** parallax. This is a major effect for the Moon, but in the
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| 41 | ** context of the limited accuracy of the present routine its
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| 42 | ** effect on planetary positions is small (negligible for the
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| 43 | ** outer planets). Geocentric positions can be generated by
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| 44 | ** appropriate use of the routines slaDmoon and slaPlanet.
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| 45 | **
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| 46 | ** 3 The direction accuracy (arcsec, 1000-3000AD) is of order:
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| 47 | **
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| 48 | ** Sun 5
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| 49 | ** Mercury 2
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| 50 | ** Venus 10
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| 51 | ** Moon 30
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| 52 | ** Mars 50
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| 53 | ** Jupiter 90
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| 54 | ** Saturn 90
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| 55 | ** Uranus 90
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| 56 | ** Neptune 10
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| 57 | ** Pluto 1 (1885-2099AD only)
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| 58 | **
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| 59 | ** The angular diameter accuracy is about 0.4% for the Moon,
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| 60 | ** and 0.01% or better for the Sun and planets.
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| 61 | **
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| 62 | ** Called: slaGmst, slaDt, slaEpj, slaDmoon, slaPvobs, slaPrenut,
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| 63 | ** slaPlanet, slaDmxv, slaDcc2s, slaDranrm
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| 64 | **
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| 65 | ** Last revision: 27 May 1997
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| 66 | **
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| 67 | ** Copyright P.T.Wallace. All rights reserved.
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| 68 | */
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| 69 |
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| 70 | #define AUKM 1.49597870e8 /* AU in km */
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| 71 | #define TAU 499.004782 /* Light time for unit distance (sec) */
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| 72 |
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| 73 | {
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| 74 | int ip, j, i;
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| 75 | double stl, vgm[6], v[6], rmat[3][3], vse[6], vsg[6], vsp[6],
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| 76 | vgo[6], dx, dy, dz, r, tl;
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| 77 |
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| 78 | /* Equatorial radii (km) */
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| 79 | static double eqrau[] = {
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| 80 | 696000.0, /* Sun */
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| 81 | 2439.7, /* Mercury */
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| 82 | 6051.9, /* Venus */
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| 83 | 1738.0, /* Moon */
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| 84 | 3397.0, /* Mars */
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| 85 | 71492.0, /* Jupiter */
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| 86 | 60268.0, /* Saturn */
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| 87 | 25559.0, /* Uranus */
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| 88 | 24764.0, /* Neptune */
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| 89 | 1151.0 /* Pluto */
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| 90 | };
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| 91 |
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| 92 |
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| 93 |
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| 94 | /* Classify NP. */
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| 95 | ip = ( np >= 1 && np <= 9 ) ? np : 0;
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| 96 |
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| 97 | /* Approximate local ST. */
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| 98 | stl = slaGmst ( date - slaDt ( slaEpj ( date ) ) / 86400.0 ) + elong;
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| 99 |
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| 100 | /* Geocentre to Moon (mean of date). */
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| 101 | slaDmoon ( date, v );
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| 102 |
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| 103 | /* Nutation, to true of date. */
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| 104 | slaNut ( date, rmat );
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| 105 | slaDmxv ( rmat, &v[0], &vgm[0] );
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| 106 | slaDmxv ( rmat, &v[3], &vgm[3] );
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| 107 |
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| 108 | /* Moon? */
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| 109 | if ( ip == 3 ) {
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| 110 |
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| 111 | /* Yes: geocentre to Moon (true of date). */
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| 112 | for ( i = 0; i <= 5; i++ ) v[i] = vgm[i];
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| 113 |
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| 114 | } else {
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| 115 |
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| 116 | /* No: precession/nutation matrix, J2000 to date. */
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| 117 | slaPrenut ( 2000.0, date, rmat );
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| 118 |
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| 119 | /* Sun to Earth-Moon Barycentre (J2000). */
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| 120 | slaPlanet ( date, 3, v, &j );
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| 121 |
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| 122 | /* Precession and nutation to date. */
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| 123 | slaDmxv ( rmat, &v[0], &vse[0] );
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| 124 | slaDmxv ( rmat, &v[3], &vse[3] );
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| 125 |
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| 126 | /* Sun to geocentre. */
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| 127 | for ( i = 0; i <= 5; i++ ) vsg[i] = vse[i] - 0.012150581 * vgm[i];
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| 128 |
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| 129 | /* Sun? */
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| 130 | if ( ip == 0 ) {
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| 131 |
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| 132 | /* Yes: geocentre to Sun. */
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| 133 | for ( i = 0; i <= 5; i++ ) v[i] = - vsg[i];
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| 134 |
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| 135 | } else {
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| 136 |
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| 137 | /* No: Sun to Planet. */
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| 138 | slaPlanet ( date, ip, v, &j );
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| 139 |
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| 140 | /* Precession and nutation to date. */
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| 141 | slaDmxv ( rmat, &v[0], &vsp[0] );
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| 142 | slaDmxv ( rmat, &v[3], &vsp[3] );
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| 143 |
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| 144 | /* Geocentre to planet. */
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| 145 | for ( i = 0; i <= 5; i++ ) v[i] = vsp[i] - vsg[i];
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| 146 | }
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| 147 | }
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| 148 |
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| 149 | /* Refer to origin at the observer. */
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| 150 | slaPvobs ( phi, 0.0, stl, vgo );
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| 151 | for ( i = 0; i <= 5; i++ ) v[i] -= vgo[i];
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| 152 |
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| 153 | /* Geometric distance (AU). */
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| 154 | dx = v[0];
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| 155 | dy = v[1];
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| 156 | dz = v[2];
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| 157 | r = sqrt ( dx * dx + dy * dy + dz * dz );
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| 158 |
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| 159 | /* Light time (sec). */
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| 160 | tl = TAU * r;
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| 161 |
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| 162 | /* Correct position for planetary aberration. */
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| 163 | for ( i = 0; i <= 2; i++ ) v[i] -= tl * v[i+3];
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| 164 |
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| 165 | /* To RA,Dec. */
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| 166 | slaDcc2s ( v, ra, dec );
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| 167 | *ra = slaDranrm ( *ra );
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| 168 |
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| 169 | /* Angular diameter (radians). */
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| 170 | *diam = 2.0 * asin ( eqrau[ip] / ( r * AUKM ) );
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| 171 | }
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