| 1 | #include "slalib.h"
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| 2 | #include "slamac.h"
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| 3 | void slaEcor ( float rm, float dm, int iy, int id, float fd,
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| 4 | float *rv, float *tl )
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| 5 | /*
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| 6 | ** - - - - - - - -
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| 7 | ** s l a E c o r
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| 8 | ** - - - - - - - -
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| 9 | **
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| 10 | ** Component of Earth orbit velocity and heliocentric
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| 11 | ** light time in a given direction.
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| 12 | **
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| 13 | ** (single precision)
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| 14 | **
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| 15 | ** Given:
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| 16 | ** rm,dm float mean RA,Dec of date (radians)
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| 17 | ** iy int year
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| 18 | ** id int day in year (1 = Jan 1st)
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| 19 | ** fd float fraction of day
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| 20 | **
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| 21 | ** Returned:
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| 22 | ** *rv float component of Earth orbital velocity (km/sec)
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| 23 | ** *tl float component of heliocentric light time (sec)
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| 24 | **
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| 25 | ** Notes:
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| 26 | **
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| 27 | ** 1 The date and time is TDB (loosely ET) in a Julian calendar
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| 28 | ** which has been aligned to the ordinary Gregorian
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| 29 | ** calendar for the interval 1900 March 1 to 2100 February 28.
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| 30 | ** The year and day can be obtained by calling slaCalyd or
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| 31 | ** slaClyd.
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| 32 | **
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| 33 | ** 2 Sign convention:
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| 34 | **
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| 35 | ** The velocity component is +ve when the Earth is receding from
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| 36 | ** the given point on the sky. The light time component is +ve
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| 37 | ** when the Earth lies between the Sun and the given point on
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| 38 | ** the sky.
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| 39 | **
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| 40 | ** 3 Accuracy:
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| 41 | **
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| 42 | ** The velocity component is usually within 0.004 km/s of the
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| 43 | ** correct value and is never in error by more than 0.007 km/s.
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| 44 | ** The error in light time correction is about 0.03s at worst,
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| 45 | ** but is usually better than 0.01s. For applications requiring
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| 46 | ** higher accuracy, see the slaEvp routine.
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| 47 | **
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| 48 | ** Called: slaEarth, slaCs2c, slaVdv
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| 49 | **
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| 50 | ** Last revision: 24 November 1994
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| 51 | **
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| 52 | ** Copyright P.T.Wallace. All rights reserved.
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| 53 | */
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| 54 |
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| 55 | #define AUKM 1.4959787066e8f /* AU to km (1985 Almanac) */
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| 56 | #define AUSEC 499.0047837f /* AU to light sec */
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| 57 |
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| 58 | {
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| 59 | float pv[6], v[3];
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| 60 |
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| 61 | /* Sun:Earth position & velocity vector */
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| 62 | slaEarth ( iy, id, fd, pv );
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| 63 |
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| 64 | /* Star position vector */
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| 65 | slaCs2c ( rm, dm, v );
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| 66 |
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| 67 | /* Velocity component */
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| 68 | *rv = - AUKM * slaVdv ( &pv[3], v );
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| 69 |
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| 70 | /* Light time component */
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| 71 | *tl = AUSEC * slaVdv ( pv, v );
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| 72 | }
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