Last change
on this file since 9223 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 | float slaRverot ( float phi, float ra, float da, float st )
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4 | /*
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5 | ** - - - - - - - - - -
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6 | ** s l a R v e r o t
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7 | ** - - - - - - - - - -
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8 | **
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9 | ** Velocity component in a given direction due to Earth rotation.
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10 | **
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11 | ** (single precision)
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12 | **
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13 | ** Given:
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14 | ** phi float latitude of observing station (geodetic)
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15 | ** ra,da float apparent RA,Dec
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16 | ** st float local apparent sidereal time
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17 | **
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18 | ** phi, ra, dec and st are all in radians.
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19 | **
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20 | ** Result:
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21 | ** Component of Earth rotation in direction ra,da (km/s)
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22 | **
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23 | ** Sign convention:
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24 | ** The result is +ve when the observer is receding from the
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25 | ** given point on the sky.
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26 | **
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27 | ** Accuracy:
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28 | ** The simple algorithm used assumes a spherical Earth, of
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29 | ** a radius chosen to give results accurate to about 0.0005 km/s
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30 | ** for observing stations at typical latitudes and heights. For
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31 | ** applications requiring greater precision, use the routine
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32 | ** slaPvobs.
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33 | **
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34 | ** Last revision: 9 April 1998
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35 | **
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36 | ** Copyright P.T.Wallace. All rights reserved.
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37 | */
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38 |
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39 | #define ESPEED 0.4655 /* Nominal mean sidereal speed of Earth equator
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40 | in km/s (the actual value is about 0.4651) */
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41 |
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42 | {
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43 | return (float) ( ESPEED * cos ( (double) phi ) *
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44 | sin ( (double) ( st - ra ) ) *
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45 | cos ( (double) da ) );
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46 | }
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